iceracer said:In reply to Robbie (Forum Supporter) :
Coolant flows too fast so it cannot absorb heat and cool the engine.
That's not how it works. Increased flow actually gives better heat transfer. In addition to simply more transfer medium available to move heat, more flow usually means more turbulence, which helps even more.
Matthew Kennedy said:iceracer said:In reply to Robbie (Forum Supporter) :
Coolant flows too fast so it cannot absorb heat and cool the engine.
That's not how it works. Increased flow actually gives better heat transfer. In addition to simply more transfer medium available to move heat, more flow usually means more turbulence, which helps even more.
Thankyou.
Paul_VR6 (Forum Supporter) said:iceracer said:There can be no pressure without restriction.
Other than the whole getting hot part, yes.
Restriction. Hot fluid in an open container will expand but generate no pressure, because it is not restricted to a fixed volume.
And usually the "help, I removed my thermostat and now my car overheats!" isn't due to the inevitable forum response of "d00d the coolant is moving too fast, it can't cool", it's because you also removed the poppet that covers the recirculation port in the cylinder head, as previously mentioned in this thread, so no coolant is actually flowing through the radiator.
Ok can I just be the first to say I was vastly underestimating the complexity and possible sources of interesting behavior in a cooling system?
Oh boy I am overstimulated now. I'm going to have to spread my thoughts out here.
1. Porsche likes their water cooled engines hot from the factory and has for a long time. We don't necessarily. I was intrigued by my '87 944's interest in running hot. There was nothing wrong with the car. I figured "Huh, emissions" and I was right after reading up on it on Rennlist. I remember the tales from the late 2000s of "944s go bang in crapcan racing" and that it was years before one was able to win since most went bang. I figured it was because they ran so hot, but it was also the rod bearing thing. Later 944s have 10.2:1 compression which is outrageous for the '80s but of course they have an aluminum block and heads. I ran 87 in mine with no knock even with its proclivity to run hot. Do modern Porsches have reverse-flow cooling? That might explain part of the boost from a 160 degree stat.
2. LT1. Low-temp thermostats are considered god-like in LT1 land. I hadn't thought about how reverse-flow cooling helps it make more of a difference on the LT1 cars which are similar in many ways to the TPI cars. LT1 is still TPI, just a newer iteration.
3. TPI (L98 350, LB9 305). Now there is much more consternation in the TPI camp about 160 vs. 180 (not much interest in 195, but a little). Pretty much everyone agrees that TPI runs too hot stock for optimal power. But TPI is too rich stock! What happened to kickstart the 160 lore right off the bat in 1987 was a magazine article about a brand new Formula 350 that was taken from the low 15s to the high 13s for like $50. They did a bunch of stuff like advancing the base timing and putting a 160 stat that people who can now tune their motors themselves through datalogging and chip burning, LS1 computer swaps or today's aftermarket engine control systems are less likely to do (but may since they can tune with those things in mind). This article and subsequent articles from the next year or two lived on in the minds of 3rd Gen F-body enthusiasts for years. The issue was that the 'stat didn't change the fan on temperatures on either side so those high 13s were only good for one run, required a bag of ice on the intake and a super long cool down afterward. Borderline useless information for autocross and truly useless on a road course without being able to change the fan-on temp. Stock the driver's fan comes on hot (around water boiling temp) and the passenger-side fan came on hotter (232 I think). Therefore you were spending very little time at 160. When I bought mine it had a 160 and the heat pretty much sucked when it was below 35 outside unless you were tearing ass.
When I started my tuning journey -- and it is one with TPI -- I determined the car was running way too cold. I had installed an aftermarket passenger's side fan switch that was supposed to turn off at 176. Years later datalogging revealed that it wasn't turning off until 140. Back to stock! You can't trust the stock gauge in absolutes, rather in relatives. See on TPI the computer gets a much more accurate signal from a another sensor in a different location than the one for the gauge! The only way to see this output is to datalog with a PC. What you want to do is sync the driver's fan on temp fairly closely with the rating of the stat in the tune. You cannot control the passenger side fan with the ECM. That is on its own switch that I haven't chosen to fool with since returning the switch to stock. I think 232 is fine as emergency fan since the driver's fan and driving airflow is enough. I now have a 180 stat, have set the fan for 182 and am happy. The car typically runs at 188-190 now unless it's cooling off from a blast. There might be a couple ponies to be had by setting everything up for 160 but the concessions to cold HVAC and exhaust stink aren't worth it to me on a street car. Lots of airflow mods and exhaust changes (which make a huge difference on TPI) to this car and 160 is still too rich with stock fuel tables but pretty close at 180.
4. 5.0 Mustang: 5.0 was lauded as advanced for its early adoption of reverse-flow cooling. How does this affect how people tune 5.0s today regarding cooling temp? Is it like LT1 where people like it cold? How many of today's cars are reverse flow?
5. Datalogging: This is the main way to find out where you're really at temperature-wise and want to be at in absence of a dyno. And after the dyno too in order to make sure you haven't screwed it up for the street or racetrack.
In reply to GCrites80s :
The rod bearing issue is well-known for 944s, Porsche had some serious issues in the oiling system.
Note that when the 944 was engineered, there was still a strong sentiment at Porsche that anything that wasn't aircooled and rear engined wasn't handed down from Ferdinand on High, and was therefore not worthy of respect. This is why the 928, a car meant to replace the 911, was never really marketed or promoted other than "hey, this is also a car we sell, buy it if you aren't man enough for a 911"
Robbie (Forum Supporter) said:In reply to iceracer :
How does no stat cause an overheat?
No 'stat or and restrictor allows flow rate to exceed the design limits of the pump. When flow rate gets outside the design range for the pump, the pump cavitates, which, ironically, reduces flow rate to the point that the coolant doesn't remove heat fast enough. Centrifugal pumps need to pump against some restriction in order to work properly.
Source: I spent 11 years in an engineering / proj mgmt role at an industrial pump manufacturer.
GCrites80s said:4. 5.0 Mustang: 5.0 was lauded as advanced for its early adoption of reverse-flow cooling. How does this affect how people tune 5.0s today regarding cooling temp? Is it like LT1 where people like it cold? How many of today's cars are reverse flow?
Subtle distinction... As I outlined before, LT1 owners were attempting to make the temperature correct, not cold. In a normal vehicle, the coolant in the block gets to 180, the stat opens, and it sends water to the radiator to cool DOWN from 180. In an LT1, the stat opens at 180 where it sends coolant to the block to heat UP from 180.
Both John Moss (godfather of the Impala SS) and Hannold Baker (or Beker... I forget... one of the engineers) from GM who worked on the LT1 were both members of a few B-body and Impala SS forums. It's not like "we're stupid and we want it cold," it was more like "the guy who bloody engineered the thing just showed up and gave us the blow-by-blow of why they had to use a 180 stat for EPA compliance, but a 160 makes the head temperatures more correct for the assembly." As it was, GM had to completely re-engineer an oil cooling system because the 180 stat needed to keep emissions where they needed made the oil too hot. The LT1 has a ton of fun little tuning things that GM had to tweak away from optimal. The only way they could keep NOx under control was to run things rich and retard timing. Then to keep HC in check they had to use a 180 stat. It was a necessity for EPA compliance within the limitations of the architecture they had to work with. It is quite common for LT1s to pick up 15-20hp if you run a leaner fuel curve, advance timing a couple degrees, and use a 160 stat. (as long as you don't mind running 91-93 octane) I'm not suggesting violating federal emission's laws, just demonstrating how far engineers sometimes have to go to comply.
It wasn't a ham-fisted attempt to get a few ponies with complete disregard for any other engineering aspects. This was a direct publication of an LT1 engineer.
GCrites80s said:4. 5.0 Mustang: 5.0 was lauded as advanced for its early adoption of reverse-flow cooling. How does this affect how people tune 5.0s today regarding cooling temp? Is it like LT1 where people like it cold? How many of today's cars are reverse flow?
Other than for strength of the physical parts of the engine (so that they can be boosted on a Mustang)- how aftermarket does tuning does not play into the design of an engine. And the only engine that's even remotely thought of for post production boost is the Mustang- so it *might* have better cooling along with the structural integrity of the block and heads to run boost.
There's zero consideration for aftermarket tuning. As a matter of fact, there's work to prevent aftermarket tuning.
BTW, the higher t-stat temp is more about fuel economy than emissions, these days. Since roughly 1996, the emissions had to be low and stable well before the engine got the the engine temp that would open the T-stat. On cycle, it takes about 200-300 seconds for the engine to get hot enough to open the Tstat at 190F, and the emissions have to be low and steady well below that.
On the other hand, fuel economy is much better when the engine, trans, and all the related powertrain is hot. (which is one of the reasons that a rad cooled trans is not smart- it takes a long time for it to get warm that way).
The "common sense" for the emissions blame came in the 80s- and that was more accurate then. Times have changed way beyond the 80s WRT emissions. For the post '96 P cars- I'm pretty confident that it does not apply relative to fuel economy. And even engine durability due to the fuel that gets into the oil and the desire to have longer and longer oil change intervals.
Curtis73 (Forum Supporter) said:GCrites80s said:4. 5.0 Mustang: 5.0 was lauded as advanced for its early adoption of reverse-flow cooling. How does this affect how people tune 5.0s today regarding cooling temp? Is it like LT1 where people like it cold? How many of today's cars are reverse flow?
Subtle distinction... As I outlined before, LT1 owners were attempting to make the temperature correct, not cold. In a normal vehicle, the coolant in the block gets to 180, the stat opens, and it sends water to the radiator to cool DOWN from 180. In an LT1, the stat opens at 180 where it sends coolant to the block to heat UP from 180.
Both John Moss (godfather of the Impala SS) and Hannold Baker (or Beker... I forget... one of the engineers) from GM who worked on the LT1 were both members of a few B-body and Impala SS forums. It's not like "we're stupid and we want it cold," it was more like "the guy who bloody engineered the thing just showed up and gave us the blow-by-blow of why they had to use a 180 stat for EPA compliance, but a 160 makes the head temperatures more correct for the assembly." As it was, GM had to completely re-engineer an oil cooling system because the 180 stat needed to keep emissions where they needed made the oil too hot. The LT1 has a ton of fun little tuning things that GM had to tweak away from optimal. The only way they could keep NOx under control was to run things rich and retard timing. Then to keep HC in check they had to use a 180 stat. It was a necessity for EPA compliance within the limitations of the architecture they had to work with. It is quite common for LT1s to pick up 15-20hp if you run a leaner fuel curve, advance timing a couple degrees, and use a 160 stat. (as long as you don't mind running 91-93 octane) I'm not suggesting violating federal emission's laws, just demonstrating how far engineers sometimes have to go to comply.
It wasn't a ham-fisted attempt to get a few ponies with complete disregard for any other engineering aspects. This was a direct publication of an LT1 engineer.
Like I just posted, the T-stat has had little to do with TP emissions since about 1996. Once the catalysts are fully working, and the a/f control is good, what the engine puts out is dealt with via the aftertreatment, not the engine out emissions. Once the regulations got hard enough, the engine out emissions mattered more in the first 100 seconds, or 50, or 30, or 20, or now 10 depending on the standard. And none of those times are even close to the engine hitting 150F. Let alone near when the T-stat opens.
And the explanation of the NOx being the problem is odd- the hotter the engine, the more NOx is made (for lots of reasons). So if engine NOx emissions were a problem, you would want to run the engine cooler, not hotter.
Curtis73 (Forum Supporter) said:GCrites80s said:4. 5.0 Mustang: 5.0 was lauded as advanced for its early adoption of reverse-flow cooling. How does this affect how people tune 5.0s today regarding cooling temp? Is it like LT1 where people like it cold? How many of today's cars are reverse flow?
Subtle distinction... As I outlined before, LT1 owners were attempting to make the temperature correct, not cold. In a normal vehicle, the coolant in the block gets to 180, the stat opens, and it sends water to the radiator to cool DOWN from 180. In an LT1, the stat opens at 180 where it sends coolant to the block to heat UP from 180.
Both John Moss (godfather of the Impala SS) and Hannold Baker (or Beker... I forget... one of the engineers) from GM who worked on the LT1 were both members of a few B-body and Impala SS forums. It's not like "we're stupid and we want it cold," it was more like "the guy who bloody engineered the thing just showed up and gave us the blow-by-blow of why they had to use a 180 stat for EPA compliance, but a 160 makes the head temperatures more correct for the assembly." As it was, GM had to completely re-engineer an oil cooling system because the 180 stat needed to keep emissions where they needed made the oil too hot. The LT1 has a ton of fun little tuning things that GM had to tweak away from optimal. The only way they could keep NOx under control was to run things rich and retard timing. Then to keep HC in check they had to use a 180 stat. It was a necessity for EPA compliance within the limitations of the architecture they had to work with. It is quite common for LT1s to pick up 15-20hp if you run a leaner fuel curve, advance timing a couple degrees, and use a 160 stat. (as long as you don't mind running 91-93 octane) I'm not suggesting violating federal emission's laws, just demonstrating how far engineers sometimes have to go to comply.
It wasn't a ham-fisted attempt to get a few ponies with complete disregard for any other engineering aspects. This was a direct publication of an LT1 engineer.
Oh I get it. It's just what needs done.
alfadriver (Forum Supporter) said:GCrites80s said:4. 5.0 Mustang: 5.0 was lauded as advanced for its early adoption of reverse-flow cooling. How does this affect how people tune 5.0s today regarding cooling temp? Is it like LT1 where people like it cold? How many of today's cars are reverse flow?
Other than for strength of the physical parts of the engine (so that they can be boosted on a Mustang)- how aftermarket does tuning does not play into the design of an engine. And the only engine that's even remotely thought of for post production boost is the Mustang- so it *might* have better cooling along with the structural integrity of the block and heads to run boost.
There's zero consideration for aftermarket tuning. As a matter of fact, there's work to prevent aftermarket tuning.
Of course. But I was asking more along the lines of what people do when they tune their 5.0s in relation to target temperature.
alfadriver (Forum Supporter) said:And the explanation of the NOx being the problem is odd- the hotter the engine, the more NOx is made (for lots of reasons). So if engine NOx emissions were a problem, you would want to run the engine cooler, not hotter.
Like I said, it is a trade off for emissions/tuning. You are correct that hot makes NOx, but it's all a dance. They may have found that increasing temps made NOx go up by 5%, but adding a bit more fuel dropped it by 40%. It's like operating a sound board. You control hundreds of little pots and faders until you get the output you need.
In the case of the LT1, dropping temps to achieve NOx was not an option for HC emissions and CAFE segment MPG. They had to get it by enrichment.
I can only give you my anecdotal evidence from running the "desert spec" thermostat in my Disco. It opens at 180 degrees. Even with towing a boat, I rarely get over 195 on a hot summer's day at 65mph. In fact, some cold days during the winter I have gotten the CEL with the "coolant temperature too low" code. Running the stock Thermostat, my truck used to run 205 to 210 without a trailer.
Most vehicles have a cooling system that is larger than it needs to be for normal everyday driving. A thermostat that starts to open earlier is also fully open earlier, allowing that over capacity to work sooner. If you ever removed a Thermostat from a car, you will know that most cars will never even get up to operating temperature without it or a restricter.
Curtis73 (Forum Supporter) said:alfadriver (Forum Supporter) said:And the explanation of the NOx being the problem is odd- the hotter the engine, the more NOx is made (for lots of reasons). So if engine NOx emissions were a problem, you would want to run the engine cooler, not hotter.
Like I said, it is a trade off for emissions/tuning. You are correct that hot makes NOx, but it's all a dance. They may have found that increasing temps made NOx go up by 5%, but adding a bit more fuel dropped it by 40%. It's like operating a sound board. You control hundreds of little pots and faders until you get the output you need.
In the case of the LT1, dropping temps to achieve NOx was not an option for HC emissions and CAFE segment MPG. They had to get it by enrichment.
The problem with that line of thinking is that you can't add more fuel to lower NOx. Not an option. You have to run stoich, and immediately around it constantly to meet the emissions requirements.
And i do understand the "dance", and know that since 1996, it's been more about a/f control to meet warmed up emissions more than every single other factor, and engine out emissions only really matters as the catalyst warms up. And the period where the catalyst is going from room temp to fully operating is way before the T-stat opens up. So the T-stat has not been an tailpipe emissions tool for a very long time.
Choosing a low-temp thermostat depends a lot on application and rationale. I doubt a lower-temperature thermostat will do much on a Boxster but a bunch of my N62 friends run low-temp thermostats because the drop in engine temp helps just that little bit with keeping the crappy valve seals alive.
Robbie (Forum Supporter) said:Ok can I just be the first to say I was vastly underestimating the complexity and possible sources of interesting behavior in a cooling system?
Robbie, you may be the first, but I doubt you will be the last to say cooling system design is complex.
Here is a link to an excellent paper written by three Ford engineers describing what goes into designing the cooling system. It may help answer some of the questions people have.
Systems Engineering Approach to Cooling System Design
The first 20+ pages are a good introduction to Systems Engineering, skip it if you don't care. The next 100+ pages explain various aspects of the different parts of the cooling system. At the very end is an interesting article describing state of the art cooling systems written in 1906. Overall an excellent introduction to the complexities and interactions in the cooling systems.
alfadriver (Forum Supporter) said:I know most enthusiasts think that the EPA is anti car- but they are not. And there are a lot of enthusiasts that work there. They can be used as a tool to make your investments actually meet their requirements.
Thank you for making a true statement about the EPA.
alfadriver (Forum Supporter) said:Curtis73 (Forum Supporter) said:alfadriver (Forum Supporter) said:And the explanation of the NOx being the problem is odd- the hotter the engine, the more NOx is made (for lots of reasons). So if engine NOx emissions were a problem, you would want to run the engine cooler, not hotter.
Like I said, it is a trade off for emissions/tuning. You are correct that hot makes NOx, but it's all a dance. They may have found that increasing temps made NOx go up by 5%, but adding a bit more fuel dropped it by 40%. It's like operating a sound board. You control hundreds of little pots and faders until you get the output you need.
In the case of the LT1, dropping temps to achieve NOx was not an option for HC emissions and CAFE segment MPG. They had to get it by enrichment.
The problem with that line of thinking is that you can't add more fuel to lower NOx. Not an option. You have to run stoich, and immediately around it constantly to meet the emissions requirements.
It's interesting to note that all LT1s had electric air pumps. Could they have been running the air pumps under certain conditions known to produce high NOx so they could add fuel to the engine and still get a stoich mixture in the exhaust?
I have never monitored LT1 air pump strategy, because I've never been curious about it until about five minutes ago. But Mazda heavily relied on the air pump on 80s rotaries so that the engines could run rich at idle and low load but still have a catalyst-friendly mixture in the exhaust system. Removing the air pump makes fuel injected models stumble and surge because the combustion chamber shape doesn't tolerate running as "lean" as closed loop operation until you get to a certain amount of load on the engine.
In reply to Pete. (l33t FS) :
Depends on what era you are talking about.
In the 80's, everyone was still learning how to make it work. And since rotaries have a special HC problem, adding air during operation is probably needed- just because there was so much Hc that the remaining oxidants had no real chance of converting it. But as knowledge got better, and a/f accuracy got better, that turned into the opposite problem- if you inject a "stoich" amount of fuel based on an O2 signal that was biased based on the injected air- you'd have a very combustible mixture in the exhaust, And that would quickly consume the catalyst via overheating.
Early in the PZEV development (late 90's, early '00's) we saw that during the cold start, running rich with air injection at the right place would end up lighting the catalyst off quite quickly with pretty low emissions. This thinking comes and goes, as the pump is pretty expensive when it's just used for about 20 seconds, let alone the long term reliabiliity issues adding an air pump into the exhaust. But it's so effective that it's still a solution that will probably be seen in cars in the next coming years- as the fleet average has to be SULEV30.
Again, dealing with FG NOx is pretty easy these days, as long as the catalyst is hot and not too damaged. I'd still like to play with a gas system where the HC and CO is virtually nothing, and most of what is left is NOx. But making that chemically efficient engine is really hard.
In reply to Pete. (l33t FS) :
I pretty sure they only run the pump for a short time on a cold start, so I believe it's more of a cat light off thing, not a NOx reduction thing.
Seems the main system for NOx reduction on the LT1 is the EGR system. I was always taught it wasn't engine temperature that makes NOx but combustion temperature, and egr is used to cool it down. In most cases, it doesn't make sense to make distinction between engine temp and combustion temp, but on an LT1 if you make the engine hotter (compared to a conventionally cooled Gen 1 sbc) but cool the head first you may not increase combustion temperature. So you may be able to achieve the other benefits of a hotter engine but still be able to control NOx with a conventional EGR system.
I'm also not a huge proponent of caring what the engineers thought, because on an LT1, once you delete all the emissions garbage and get a good tune, it is a whole different engine, more power, more reliable, and better economy.
In reply to alfadriver (Forum Supporter) :
Intentional afterburn in the exhaust was a lot of the emissions cleanup strategy, to the point that the exhaust manifolds were shaped like burn chambers. Before 1981, they didn't even need catalysts, but relied so heavily on rich mixture + air that they had a cooling jacket around the manifold.
LT1s had a single catalyst mounted very far back from the engine in typical 70s-80s GM fashion, I'm not sure if this would be enough time to prevent the cat from doing all of the heavy lifting. And, either way, it's all completely conjecture.
GM did some weird things in that timeframe. Pre-OBDII TBI V6s in trucks would go open loop at idle after a few seconds and start adding fuel. It's been so long ago since I had this explained to me that I've forgotten the rationale, if it was for idle quality or for catalyst cooling.
In reply to Opti :
I wouldn't call it "emissions garbage"... It was a lot of necessary band-aids to limp a 1950s engine past 1990s targets. That is why the LS engines are such a breath of fresh air, they are much more naturally clean because the rings seal better, the combustion chambers are better, the intake port geometry is better (which ties into combustion chamber function), the materials are better, the ignition control is vastly better...
In reply to Opti :
EGR hasn't been a gasoline TP NOx tool for a long time. For the last 20 years, it's a fuel economy tool. Add the pumping loss, plus the higher potential compression vs. the combustion delay- and the net overall is more efficiency.
Cooled EGR makes that even more effective.
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