Engine running hot - check my thinking

After the bike disabled itself, I got to take the DSM to work this morning, which didn't turn out so good either.

Background

My commute goes over a pass and on the long uphill stretch this morning, I noticed that after running under load about halfway up (call it 5-6 minutes) the coolant temperature started creeping up until the check engine light came on (which it does, according to ECMlink, at 234F). Fans etc were audibly running at this point, even though I should have enough airflow through the (uprated) radiator which admittedly sits behind a rather large intercooler. At that time I was running probably 3-4psi of boost at 1/3 throttle at 3k-4k rpm (bigger turbo as well, so that's about 1/3 boost) doing about 40mph, so nothing that should both the engine. By the time it was safe to pull over the data logger suggested water temperatures in excess of 250F and the engine oil was quite literally smoking hot (some of smoked off the dipstick). Letting the engine idle didn't seem to make matters any better so I quickly turned it off even though the turbo probably didn't like that. Coolant temperatures appear to be moderately normal when coasting downhill or on roads with little elevation changes.

I've drive the exact same route at similar speeds a week or so ago without any problems, but the outside temperature was about 10F lower then. No other changes apart from me getting the ECU to talk to ECMlink (but I only looked and didn't touch anything, I swear).

No signs of low coolant or oil and fortunately so far no signs of them mixing.

The real question:

Given that I've got the laptop with ECMlink on me anyway, I figured I'll datalog my way back - I'll be nursing the car but hope that I can get some insight as the way back includes a shorter uphill stretch.

Unless there's an issue with the cooling system my thinking is that increased engine temperatures are moderate load would suggest either:

• Running too lean
• Too much ignition advance, even though I can't hear any knocking. But then again the exhaust is a little on the loud side
• Turbo producing so much heat under constant boost and that's pushing oil and water temps up. That would be a bit strange though that 10F difference in outside temperatures would push it over the edge and it would make the car unusable as a track car out here for track with actual corners in them.

Haven't got a wideband installed yet but I figured I'll try to log at least the following data:

• Water temp
• Throttle
• Boost/MAP if I can
• Knock
• Ignition advance if I can
• narrowband O2, to see if it's at least switching or suggesting it's running permanently lean

Anything else I should try to log that might give me a clue as to what's going on? Anything blindingly obvious (aside from me need to buy better condition vehicles) that I've forgot to mention?

Sounds like you have a good diagnostic handle on it. Only thing I can suggest off the top of my head is to add some Water Wetter. At those temps you're certainly developing steam pockets inside the cooling system, which will makes things worse. If this persists you might want to switch to a cooler thermostat for the summer. Might help a bit.

Water wetter sounds like a good idea, I'll try to pick some up tomorrow. I think the thermostat is already on the cold side but I'll keep that in mind. Maybe it's also time to just stick a good new one in.

One thing I forgot to mention was that the water pump was changed recently, but the last time I drove the car to work it already had said new water pump. That said, any sort of obstruction in the cooling system would create similar symptoms, correct?

Hmm. Makes me wonder. I recently replaced the water pump in my Protege. I noticed over the following week or so that I needed to add coolant to the coolant tank because the coolant level was below the 'Low' line of the tank. I'm assuming it's because some air was getting purged. You sure your coolant level is where it should be?

One other idea - water pumps depend on engine speed. I wonder if dropping down a gear to get more coolant flow through the radiator might help.

When I went out at lunchtime the engine wasn't cold enough to check the coolant level. The level in the recently retro-fitted header tank looks OK and moves depending on engine temperature. I'll have a look at the coolant level before driving back, though.

I tried the "increase engine speed" going uphill but that didn't help a lot.

You have the classic symptoms of too little coolant flow through the radiator or too little air flow through the radiator. Either the coolant flow is obstructed, probably due to mineral deposits, or the radiator is too small. Or the air flow is blocked by debris, bent fins, or some such impediment.

I don't think the radiator is too small - it's one of the bigger aftermarket units that still fit the original mounts, but (at a guess) has at least a 1/3 more coolant capacity. That said, I don't think you're necessarily that far off as it feels like a recently developed coolant or airflow problem. I guess I'll better check for flow obstructions between the intercooler and the radiator, too. And order up a new thermostat...

Is the recently replaced water pump high quality, or a cheapy? May be the impeller is loose on the shaft. Also, you could be in the early stages of a head gasket failure; when you start the car up in the morning does it pressurize the cooling system before the temp gauge starts moving? Not all HG failures result in mixed collant & oil, exhaust gasses in cooling system is also fairly common, but I'm not sure that would explain the 250 degree temp.

It looks like it's a little low on coolant (but we're only talking a pint or so). The cap also looks a little ropey so I'll top up the coolant tomorrow with water wetter and get a new cap, plus I'll get a new OEM thermostat just in case.

The datalog shows a little too much knock in several places for my liking so I need to figure out where I need to pull the timing back a little. Hooray for crappy 91 octane gas...

Other than the knock the datalog looks reasonably clean, so I guess I need to look more at the mechanical side of the cooling system.

It also looks like the IAT sensor either isn't hooked up any more or it's non-functioning because I'm pretty sure that the incoming air was slightly warmer than a constant 77F despite the huge intercooler.

HappyAndy wrote: Is the recently replaced water pump high quality, or a cheapy? May be the impeller is loose on the shaft. Also, you could be in the early stages of a head gasket failure; when you start the car up in the morning does it pressurize the cooling system before the temp gauge starts moving? Not all HG failures result in mixed collant & oil, exhaust gasses in cooling system is also fairly common, but I'm not sure that would explain the 250 degree temp.

Good question re the waterpump - IIRC it's a regular parts store one, not an uprated or OEM one.

I'll see if I can figure out if it's pressurizing the cooling system; that might be another avenue to investigate.

I would not be surprised if the head gasket is on its way out given that I've had a few cooling system issues when I got the car. Oh well. That'll be an excuse to install an uprated head gasket I assume.

Have you considered a leakdown test? That way you know it's a headgasket leak because your motor would be cool and your coolant would pressurize.

BoxheadTim wrote: The level in the recently retro-fitted header tank looks OK and moves depending on engine temperature. I'll have a look at the coolant level before driving back, though.

This is where I'd start, along with putting in a new T-stat

All the cars I've had never had the coolant levels go up & down depending on engine temps. Sounds to me like a sticking T-stat

My bet is Head Gasket BUT

When you start the car cold try putting your hand on the rad in various places to see that it heats up evenly. My FC had a cooling problem that turned out to be the rad was partially clogged and only about 1/3 of it was actually allowing coolant to pass through it. By placing my hand on it as the car warmed up I was easily able to tell where the clogged tubes were.

Otherwise the suggestions that others have made are spot on.

I would remove the plugs and pressurize the cooling system and see if it holds pressure. If it does not hold pressure look for the cylinder that has coolant in it. If it holds pressure you are not 100 percent out of the woods but the odds of a head gasket are much less.

Way back in t3h Dark Ages of the mid 1990's I went to Colorado with some buds, we were driving a Dodge Caravan with the Mitsubishi V6. It did perfect all across this great land until we hit the higher elevations in the Rockies, then it overheated on every uphill grade. This was with ambient temps in the low to mid 80's. We pulled over and let it cool each time, we eventually removed the thermostat, no improvement. We struggled on till we reached Silverton and dropped it at the local one hole gas station to have it checked out. The guy there said 'get used to it', whaaa? The stock radiator was about twice the size of a paperback book and was fine in the thick air of the lower elevations but in the thinner air around 6000 feet and up it just wasn't up to the job. Said he saw them do that all the time. We didn't use the van the rest of the week until we went back to SC, sure enough once we got below ~6k feet elevation the overheating problem went away. When the van was sold 4 or 5 years later, it still had never overheated again.

So based on that experience and your description I'm going to say that even with the bigger radiator etc you are having a problem with airflow through it or heat exchange once the air is there.

On Jensen Healeys, they are known for running hotter than normal at highway speeds. They came originally with a two core radiator but there is a 3 core replacement. Mine was doing that, so out came the 2 core and in went the 3. Still the same problem, it would run around 210 on the highway and sit right at 180-185 in traffic or low speeds. It turns out a similar problem can be caused by the shape of the air intake slot below the bumper, the fix is to make 100% sure that every atom of air coming in that slot cannot go anywhere but the radiator (add aluminum sheet shrouding, etc between the air slot and the radiator) and add a front lip spoiler or a sheet metal splitter at the bottom of the car to act as a 'scoop' to channel even more air through the radiator. On my car with a 180 deg T stat, the coolant temp on the highway dropped to around 185 by doing the splitter mod.

You have probably already done this stuff, but here are my thoughts.

1) bleed all the air out of the coolant. some motors have provisions for doing this easily.

2) swap in a known, good, thermostat

3) investigate the weight of oil you are using in the summer heat

4) flush out your coolant system and put in a proper mix of distilled water and anti-frizzle

Only then would I tackle other things.

I honestly think Water Wetter is a fantastic product, but I would only use it as insurance, not a fix.

Knock, running hot... is the mixture lean?

That's what I'll be looking at next - got to go and install a wideband. I'm thinking that under certain circumstances it's either running too much advance or is running lean. That said, I can see the NB O2 switching under load so it's not running too lean under load condition but around stoich (which might be too lean under the load conditions).

What really concerns me at the moment is that under acceleration at one point, the ignition timing pull-back due to knock was in the order of 10 degrees for a couple of seconds which suggests to me that I either have a fuel quality problem or the timing is way too aggressive under normal driving conditions.

I'll go through some of the basics today - ignition to ensure I've got the right grade of plugs fitted, plus the basic coolant stuff (although I'll have to get a T-stat from the Chrysler dealer instead of an aftermarket one, so I won't be able to fit that for a few days). I'll also try and check for obstructed airflow through the radiator again as well as I can without taking the front end off.

After that I might get the cheap HF leakdown tester to see if it's pressurizing the coolant when the engine is cold.

cdyer77 wrote:

BoxheadTim wrote: The level in the recently retro-fitted header tank looks OK and moves depending on engine temperature. I'll have a look at the coolant level before driving back, though.

This is where I'd start, along with putting in a new T-stat All the cars I've had never had the coolant levels go up & down depending on engine temps. Sounds to me like a sticking T-stat

Coolant level going up and down is normal in a system with an expansion tank (which this one is). I haven't ruled out the T-stat, though.

In reply to Curmudgeon:

Getting used to it isn't really an option, given that I'm planning to use the car for occasional track use. The local track is out in the desert, too, so it's gets even hotter out there...

Some additional shrouding might be helpful, though.

To save you some time with the dealer the t-stat part number is MD997608, list price of $23.00.

Thanks - according to the local Chrysler emporium that's showing as discontinued but I should hear today if they can get it still.

After some more digging around the car I couldn't really find anything that looks like an immediate OMG headgasket failure, even though I'm still not ruling this out. I did however find a bunch of potential issues I really didn't like:

• It looks like the knock sensor is getting triggered even if you rev the engine without any load. I did hear what I think was the exhaust heat shield rattling so I'll have to investigate if that's tripping the knock sensor, especially as it doesn't really make use of all the available mounting lugs
• The turbo on the car is only oil cooled, despite the car having fittings for a water cooled turbo. I guess this isn't doing much in the way of keeping the oil temp down and despite the big turbo the car doesn't have an oil cooler. That can't be good...
• Obviously I'll try to swap out the thermostat when/if I get a new one.

I'll try to take off the heat shield (a task not being made easier by the fact that the pyrometer fitting is threaded through it and is proving a PITA to remove) and see if that does change anything re the knock sensor. There are a bunch of other sources of rattles around the drivetrain like the exhaust so I guess I'm better off trying to address those first before I check the knock sensor which admittedly is known for going bad on these.

It sounds like your knock sensor with excessive advance is the root of all evil. Since the fittings are there already, you might want to look into what it would take to get the coolant lines to the turbo. Add an oil cooler when you can, and, the ducting to the radiator can surprisingly effect how well the radiator works. I'd make sure all the ducting/shields are in place.

Lastly, as a last resort. Take the windshield wiper hose and reroute so it sprays the front of the radiator. It's a temp fix, but it just might get you over that hump. A couple of squirts or more when things really start to get hot. Pinched brass tube in front of the radiator to spray the fluid. Yeah, sounds wacky, but, coolant is coolant.

BoxheadTim wrote: Thanks - according to the local Chrysler emporium that's showing as discontinued but I should hear today if they can get it still.

Chrysler may have discontinued it but it is still available through Mitsubishi.

as a "tuner" (i dyno tune cars) i see a few issues.

one being your IAT sensor. if its showing cooler than actual intake temp, you will get more timing than you should.

also, you dont need to hear knocking to have too much timing for building heat. knocking is near the maximum power the engine will make. 99% of turbo cars are tuned/built/driven for short bursts of acceleration. coolant temp will climb during a 1/4 mile run, but not fast enough to cause a problem.

i am shaking my head at you playing with your tune with out a wideband. that narrowband is 110% useless for this. the all mighty 14.7:1 is for idle and cruise only. any acceleration should be richer than that. your narrowband should show rich only during acceleration, but switch back and forth during cruise/idle.

another afterthought on timing. spark plug/piston top readings are your only real gauge as to whats going on. knock sensors are garbage, plain and simple.it is a microphone tuned to pick up one frequency. im not trusting my engine to that. if that engine has ever been opened, you mill the head, change pistons etc, the tone of the knock changes and that sensor is useless to you.

post up some data log screen shots starting before it gets hot to when its hot and also when it gets hot, pullover, pull a plug or two and take good clear pics. that should give me a good idea of whats going on

Um, simple question, but did the radiator in stock location have any ducting between the body and the radiator that was removed to fit the IC? I ask because many modern GMs (as an example) absolutely require the ducting at higher speeds to provide enough airflow through the radiator. I learned this on my Eldorado when I had remove the lower duct piece of plastic when doing a repair and failed to put it back on, highway temps went from 200-220 range to 240...

That and get a wideband, if you can datalog (usually the expensive part) the sensor itself is cheap $50...