Can someone explain to me the "lower temp thermostat"?

So I get the general idea. 160deg stat opens earlier than 180deg stat. But generally I put them with pod filters from pep boys - a solution to a problem that doesn't really exist, or at best a band-aid for not fixing the root cause.

But then Classic Motorsports goes and installs one in their Boxster S because their expert insists, and the main reasoning given is "florida". This shakes my understanding of thermostats to the core.

1. Did porsche really not consider that people would drive their Boxster S' in anger in Florida?

2. In my admittedly limited understanding, a lower temp thermostat would lower the temperature the engine coolant hangs around at. But a lower temp thermostat would not have any impact at all on the overall cooling systems ability to shed heat. So while the thermostat might lower your cruise temp, it would have no affect on maximum cooling ability, like on track in florida when you are actually generating maximum heat.

3. Hot oil generally flows better. So low temp thermostats I'd think can actually put your oil at the wrong temp, making it harder to flow to all the nooks and crannies and maybe costing you some HP in pumping losses?

So, is there real benefit to lower temp thermostats? 

(Let's not even get started on how a sub 70k mile porsche needs over $3k in parts alone and a clutch job with engine out labor before it is track ready, and that is not including the IMS stuff perviously done, yikes!)

Robbie (Forum Supporter) said:

But then Classic Motorsports goes and installs one in their Boxster S because their expert insists, and the main reasoning given is "florida". This shakes my understanding of thermostats to the core.

I did not know they did this, but I am in agreement.  Following this to see what the explanation is. 

I don't see how there is a real benefit to a lower temp thermostat.

If you go look on the internet you'll find a lot of discussion over whether or not it's really a good idea for the boxster too. I personally considered it on mine and chose not to but I have no data to support either side (and it ran hotter than I would have liked but not unreasonable and never overheated...also had who knows how old coolant in it because I was terrified of bleeding the system). The thing that I think causes a lot of confusion is that thermostats tend to be identified by a single number, but aren't necessarily an on/off switch and it's not always clear what that number represents. If that 180* tstat is fully open at 180, then yeah, a colder thermostat is just going to make the engine warm up slower. But if it starts opening at 180* and isn't fully open until 210*, then a colder thermostat should regulate the temperature lower (in all honestly this still feels like a bandaid, but does work at least under the right conditions). Also depends on if the cooling system is designed to be regulated by the thermostat, fans, or some combination of both. I'm honestly not sure where modern cars fall on that spectrum.

Regarding Porsche 986/996, I have read the answer many times. Here are a few quotes:

From Wayne Dempsey (Founder of Pelican Parts):

Charles at LN Engineering ran dyno tests on the car before and after the installation of the lower-temp thermostat, and he found a +5 HP change with the lower thermostat. He believes (and I tend to agree with him), that Porsche set the cars to run hotter so that they could boil water and other contaminants out of the oil in order to provide for longer oil life and less frequent changes (mandated by governments, etc.). I tend to believe that frequent oil changes, and the addition of the low temp thermostat is a positive upgrade for these cars.

Some other things to think about - the 3rd radiator. If you install the 3rd radiator, then the cooling effects won't be fully utilized until the thermostat opens up completely. The stock t-stat with the 3rd radiator will act to artificially inflate the operating temp of the engine because the t-stat will close back up when the coolant is cooled down below the opening point. Also important to consider are the cooling fans. Although the low-temp thermostat opens at 160 or so, the fans won't kick on until the temps get much higher. You can trick the car into putting the fans on earlier, but in most cases that is not necessary.

-Wayne

From "JFP_in_PA" (on the 986Forum):

These engines run way too hot with the factory thermostat, primarily for emissions purposes. Lower the coolant temperatures also dramatically lowers the oil temperatures, the oil lives longer and does a better job as the result, without impacting the car's emissions one iota.

Keeping the engine cooler also help the engines thermal efficiency, reducing spark knock, and helping it run harder. Every GT car, cup car, and all the factory turbo cars came with a 160 F thermostat.

And no, you won't see much of a change on the dash display, but that is due to the gauge's rather poor accuracy. Realistically, your engine will have dropped from around 210-220 F to around 170-175 F, will actually warm up quicker, and will still have tons of heat in the winter.

From Jake Raby (on Rennlist):

... Nothing has proven to keep cylinders straight and more round than reducing coolant operating temps by a few degrees. This is especially true for cylinders 2 and 5, where they are situated between cylinders, and see the hottest coolant, for the longest period of time.

Its not just the overall temperature of a Tstat that matters when developing a better mouse trap. How much the unit will bypass when cold, how soon it starts to open, and the temperature that it is fully open are all what required special attention.

I see factory engines with bores .010" oval by 100K miles, which is ridiculous. This is our normal findings, as Charles measures every block that goes to LN before machining, and notes mileage. Generally bore will gain .001 ovality and .0005" taper per 10K miles.

When developing the low temp Tstat we faced lots of ridicule, but we've never seen someone remove the low temp unit and go back the other way. The general consensus of "if the factory didn't do it" is the biggest wall that a developer has to face. Quite frankly, I don't give a damn what the factory did, or why they did it.

Yes, coolant temp matters in regard to enrichment, as well.. There's a point where the CLT can make serious power, I have observed a 15 degree window where the engine makes the most power, and coincidentally, the engine moves to a different fuel map for this window. You learn this from having to chase maps while developing ECU flashes from scratch. When Beth was Land Speed Racing her 996 I would work very hard to keep the car at an exact temp, around 4-6 degrees below the sweet spot while we were in line to make her run. That meant foreign the car up, shutting it off and doing what we could to keep the engine where I wanted it to be. When she'd launch, the entire run would usually complete before the temp was out of the sweet spot, netting the most power. It took me about 6 trips to the track to figure this out, and hours of studying datalogger and dyno plots. ...

There aren't many high performance cars that can actually shed heat faster than they can make it. Pretty much any fast car, when you floor it you are starting a (fairly long) countdown to overheat or some side effect of it (like detonation). Starting that run at a lower temperature extends the timeline.  That's not the entire benefit, but the more powerful the car the bigger the effect that is, right up until your 160* thermostat turns into having full control of an electric pump water instead.

The traditional thought (going back to carbed engines) is that the hotter an engine, the better MPG, but the cooler running an engine the more HP.  Mainly due to head temp and any heat absorbed by the charge, I believe but could be wrong.

Basic thermo thought experiment as well, isn't it?  Same engine, increase delta-T and you get more from the larger heat transfer, right?  I never was any good at thermo problems.

It mostly does nothing unless your engine loads are low enough/airspeed is high enough that the coolant temperature is hovering around thermostat temperature.

Engineering an engine to run hotter, besides economy and power benefits, also allows the radiator to be a lot smaller/require less airflow, because it's easier to remove BTUs from 220F coolant with 90F air than it is from 160F coolant.

In reply to AAZCD (Forum Supporter) :

It's interesting to see so many internet engineers second guess Porsche's.

I've said it before, I'll say it again- "common sense" is wrong sometimes.

And leave it at that.

alfadriver (Forum Supporter) said:

I've said it before, I'll say it again- "common sense" is wrong sometimes.

I would love to hear more about this from your experience, as I am sure you've done some actual experimentation.

I have done dyno testing with no thermostat and PWM controlled waterpumps where we can target an actual coolant temperature. It seemed that the test engine (VR6 making around 280whp at the tires) would swing about 10whp going from 160F to 195F with best power being right around 175F. Power started to fall off more on the top end than the bottom end. We had to add a little fuel to keep AFR in check below that, and remove some past that and didn't make any timing changes during the testing. I think on a car that's run hard and prone to heat soak the low temp tstat is a bandaid to get the coolant temp where you actually want it, vs making sure the rest of the cooling system is up to task.

I remember when I bought  a 160 degree thermostat about 20 years ago for one of my vehicles. 

The advertising copy said  running at the lower temp would fool the computer into running the engine a little richer than with the standard thermostat, therefore making more power.    This was on an 97 Ford Ranger with 4.0 Liter, that had a whopping 160 hp stock, so I was desperate.      I didn't notice any change and ended up putting the stock one back.   

In reply to Paul_VR6 (Forum Supporter) :

I agree that a cooler engine can make more power, especially if it's knock limited.

But the whole "it's dangerous to run hot" when hot is 220F is BS.  And when you can run good spark (like most DI engines can), the hotter the chamber, the better the fuel economy- both because of better combustion as well as lower engine friction.  And that's where "common sense" falls apart.

In the real HD testing I've been doing recently, seeing 230 isn't a big deal.  Systems are designed around doing that.

And going forward- one thing that we will see soon- no power enrichment at all.  So not only will the engines be running at 220F, they will be running stoich.  I've seen plenty of posts that suggest that engines can't do that, even though they have been tested that way for a long time- the only problem *right now* is very long term valve seat recession.  And there are materials that can deal with that.

Going back over my career- I can't say that I fully agree with Porsche engineers, better than Lotus or Coswrorth- but that's a pretty low bard.  But I trust all of them far more over internet engineers.

alfadriver (Forum Supporter) said:

In reply to AAZCD (Forum Supporter) :

It's interesting to see so many internet engineers second guess Porsche's.

I've said it before, I'll say it again- "common sense" is wrong sometimes.

And leave it at that.

The people I quoted are well known in the Porsche (owner) community and have credentials other than "internet engineer". I have bought and wrenched on plenty of troubled Porsches and other VAG cars. I have replaced IMS bearings. I currently enjoy a 'Dieselgate' TDI VW. I am no expert, but I do not believe that all cars are designed with the benefit of the consumer over the benefit of the shareholders.

*Edit* -  deleted: optimal performance for the consumer as top priority.

In general, many people have the belief that a colder engine makes more power.  In some cases that's true, but in many it's not.  And people are also afraid of high coolant temps.  I've had people in the Mopar V8 tuning community freak out at me still having a 195* t-stat in my Jeep, as everyone swaps to a 180 before tuning anything. 

For hot running engines, BMW started doing it on some of their engines years ago.  The M62TU in my E38 sits in the 215 - 230* range normally. 

All of that said, there's always the possibility that a specific engine design may have an issue that could be delayed or avoided by a change of operating temp. 

I'm skipping all of the legitimate discussion above to post the actual reason I've used lower temperature thermostats.  On both of my previous trashy rally cars (RX7 and Merkur), once a special stage started it was just a matter of time until the temp gauge was going to be pegged.  Since the car could almost always get back down to the thermostat temperature during transits, the lower temperature thermostat gave me a lower starting temperature and therefore bought another 30 seconds or so of full throttle before I had to worry about boiling the engine.

AAZCD (Forum Supporter) said:

alfadriver (Forum Supporter) said:

In reply to AAZCD (Forum Supporter) :

It's interesting to see so many internet engineers second guess Porsche's.

I've said it before, I'll say it again- "common sense" is wrong sometimes.

And leave it at that.

The people I quoted are well known in the Porsche (owner) community and have credentials other than "internet engineer". I have bought and wrenched on plenty of troubled Porsches and other VAG cars. I have replaced IMS bearings. I currently enjoy a 'Dieselgate' TDI VW. I am no expert, but I do not believe that all cars are designed with optimal performance for the consumer as top priority.

Unless they have been doing actual automotive based engineering, with an actual engineering degree, they are internet engineers.  Sorry.

edit- engines are not designed with just peak power in mind.  Especially when peak power is such a very, very, very small part of what an engine does.  Even add up all of the P cars that have just been race cars all of their lives, the sum of peak power operation of P cars is probably less than 1% of the time.  Optimum performance is different for all manufacturers, but other than the advertising, peak power is not that big of a deal.  

¯\_(ツ)_/¯ said:

I'm skipping all of the legitimate discussion above to post the actual reason I've used lower temperature thermostats.  On both of my previous trashy rally cars (RX7 and Merkur), once a special stage started it was just a matter of time until the temp gauge was going to be pegged.  Since the car could almost always get back down to the thermostat temperature during transits, the lower temperature thermostat gave me a lower starting temperature and therefore bought another 30 seconds or so of full throttle before I had to worry about boiling the engine.

In this case, why bother with the thermostat at all?

In reply to ProDarwin :

Keeping it warm enough on transits that I wasn't starting special stages with a dead cold engine and hurting things that way instead.

alfadriver (Forum Supporter) said:

AAZCD (Forum Supporter) said:

alfadriver (Forum Supporter) said:

In reply to AAZCD (Forum Supporter) :

It's interesting to see so many internet engineers second guess Porsche's.

I've said it before, I'll say it again- "common sense" is wrong sometimes.

And leave it at that.

The people I quoted are well known in the Porsche (owner) community and have credentials other than "internet engineer". I have bought and wrenched on plenty of troubled Porsches and other VAG cars. I have replaced IMS bearings. I currently enjoy a 'Dieselgate' TDI VW. I am no expert, but I do not believe that all cars are designed with optimal performance for the consumer as top priority.

Unless they have been doing actual automotive based engineering, with an actual engineering degree, they are internet engineers.  Sorry.

 

Apology accepted. ...and just to note, the Porsche 986 S that Robbie was asking about in the original post and the quotes I posted are specific to the M96 engines - not implying that a low temperature thermostat is optimal for all designs.

I just got off of a 12 hr night shift and am not feeling smart or witty. For the rest of the morning the internet can be wrong while I nap.

alfadriver (Forum Supporter) said:

In reply to Paul_VR6 (Forum Supporter) :

I agree that a cooler engine can make more power, especially if it's knock limited.

But the whole "it's dangerous to run hot" when hot is 220F is BS.  And when you can run good spark (like most DI engines can), the hotter the chamber, the better the fuel economy- both because of better combustion as well as lower engine friction.  And that's where "common sense" falls apart.

In the real HD testing I've been doing recently, seeing 230 isn't a big deal.  Systems are designed around doing that.

And going forward- one thing that we will see soon- no power enrichment at all.  So not only will the engines be running at 220F, they will be running stoich.  I've seen plenty of posts that suggest that engines can't do that, even though they have been tested that way for a long time- the only problem *right now* is very long term valve seat recession.  And there are materials that can deal with that.

Going back over my career- I can't say that I fully agree with Porsche engineers, better than Lotus or Coswrorth- but that's a pretty low bard.  But I trust all of them far more over internet engineers.

Thank you for the explanation, that does make some sense. Another argument I have heard is lower temp helps longevity of the engine plastics, which is different than some of the other arguments above. Not sure I believe it as I am suspect of any plastics as they seem to like to fail pretty brand agnostically. 

Would like to hear more about the seat issues, and how quickly (nor not) that happens. 

 Ive installed one in was a 4th gen camaro with an LT1. The stock high speed fan came on at like 236*.  In the TX heat if you were beating on it the temp would creep up pretty high, and you would get some knock retard.

I installed a 160* but also dropped the fan temps, and the normal operating temperature did come down quite a bit, and was much less prone to fluctuation when hammering on the car. KR was reduced in the summer heat. 

I may be kind of an odd platform though, because even with the cooler temps, heater effectiveness was not changed, and in many other cars Ive seen with cooler thermostats the heater becomes a lot less effective.

I cant see how a cooler thermostat alone would help without also changing fan controls (with electric fans)

In reply to Paul_VR6 (Forum Supporter) :

Materials on old engines are not all that happy running really hot- so they wear away.  Not sure how fast it happens, as I have not seen the data directly, but I know that's the big concern for many engines as we can run less and less enrichment.

There are new materials that can deal with that, so for new engines, I have no real concern over it.

¯\_(ツ)_/¯ said:

I'm skipping all of the legitimate discussion above to post the actual reason I've used lower temperature thermostats.  On both of my previous trashy rally cars (RX7 and Merkur), once a special stage started it was just a matter of time until the temp gauge was going to be pegged.  Since the car could almost always get back down to the thermostat temperature during transits, the lower temperature thermostat gave me a lower starting temperature and therefore bought another 30 seconds or so of full throttle before I had to worry about boiling the engine.

Well this is a good point and this is why they work as a 'bandaid'. If your cooling system can't keep up with WOT heat but can keep up with idle or cruise heat, then bringing the water temp down lower in between WOT bursts gives you more thermal 'headroom' before you have issues. 

alfadriver (Forum Supporter) said:

In reply to Paul_VR6 (Forum Supporter) :

Materials on old engines are not all that happy running really hot- so they wear away.  Not sure how fast it happens, as I have not seen the data directly, but I know that's the big concern for many engines as we can run less and less enrichment.

There are new materials that can deal with that, so for new engines, I have no real concern over it.

Good to hear as I seem to be working more and more on these DI engines that have similar lambda targets (though not quite as aggressive) and the owners are looking for quite rowdy power levels. PS the internet engineer comment was worth a chuckle on a rough day, so thank you for that as well

Robbie (Forum Supporter) said:

¯\_(ツ)_/¯ said:

I'm skipping all of the legitimate discussion above to post the actual reason I've used lower temperature thermostats.  On both of my previous trashy rally cars (RX7 and Merkur), once a special stage started it was just a matter of time until the temp gauge was going to be pegged.  Since the car could almost always get back down to the thermostat temperature during transits, the lower temperature thermostat gave me a lower starting temperature and therefore bought another 30 seconds or so of full throttle before I had to worry about boiling the engine.

Well this is a good point and this is why they work as a 'bandaid'. If your cooling system can't keep up with WOT heat but can keep up with idle or cruise heat, then bringing the water temp down lower in between WOT bursts gives you more thermal 'headroom' before you have issues. 

However, it has the downside of bigger temp swings.  I figure the temp and pressure swings are a bit hard on things, particularly any plastic in the system.  So whenver possible, I prefer to upsize the radiator, improve airflow, etc. to minimize the swings.  And if it gets more than 20* above t-stat temp in anything other than extreme conditions (and I'm happy with the temp it's topping out at), then the t-stat is too cold. 

AAZCD (Forum Supporter) said:

From Jake Raby (on Rennlist):

Quite frankly, I don't give a damn what the factory did, or why they did it.

I know this part of his statement is mostly just peacocking, but I will say that this really rubs me the wrong way. If you don't seek to understand, then it is likely you will not understand. It doesn't make me trust what he says, it does the opposite. 

Now it certainly seems like he has lots of experience racing and has spent hours on the dyno. And he has outlined the benefits of lower coolant temp (less ovaling of cylinders 2 and 5 and more power). But he has not explained HOW a lower temp thermostat actually does that. 

We all have to remember that the thermostat does not regulate coolant temp at all anymore once it is fully open.

It could be as simple as "a lower temp thermostat opens FURTHER, therefore allowing MORE coolant flow when fully open" this would make total sense to me how the lower temp thermostat could help in racing a track situations. But no one ever says that...