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backwards overheating problem

2K views 15 replies 5 participants last post by  A.Cabral 
#1 ·
Hey guys, I've been through quite a bit with my '92 2.6 Sportline trying to get it to run cool. Replaced the water pump and eventually the radiator (it was clogged, one side cool and the other hot). Had lots of air in the system which I presumed was me not bleeding it properly after all the flushing and replacement of components, since I'm a relative novice and did it myself. I am not losing coolant fluid though, so the system isn't leaking. My local mechanic (european car specialist) said I had a ton of air and bled it off for me. He said if I get air again I may be looking at a deteriorating head gasket.

BUT HERE'S THE BACKWARDS ISSUE:
When I turn my heat on.... temperature spikes. Did I break physics? Is there a tear in the space time continuum somewhere around my heater core?
Heat works fine though. Blows hot and cold when it should. A/C also works fine.

I run a lot of highway miles, and she handles that fine. As per usual it's the bumper to bumper stuff (plenty here in Atlanta) that kills me. But time and again on the highway I can be running 70-80mph comfortably at ~80C ... flip on the heat and watch the needle drift anywhere up to 100. At highway speeds this drops back down when I turn the heat back off.

My mechanic doesn't believe me. I'm taking it back to him tomorrow for a brake job so I'll probably ask him to do a bleed as well and see if I got more air.



After the radiator replacement and bleed it got quite cold for a while so there really was no issue. But we've been having an early spring out here and I never make it home off the highway without my fans heaving (yes they work) and my temp needle well over the 100 mark.


Side note: I love this car and it's an excellent survivor at 167k miles. I have however felt the lack of power... If I'm looking at a head gasket job, i might as well do a rebuild. But if I do a rebuild I would at least look into a swap to a 300sl m104 and 5 speed instead. I'm actually more afraid of the 5 speed swap which will be necessary to handle the power. Any thoughts are welcome. Unless you're going to preach the gospel of keeping it original.:devil
 
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#2 ·
Mezarri, not sure if the 2.6 to 3.0 upgrade is a big difference in power unless the 3.0sl you talk about has 24 valves. Does the 3.0-inline even fit?, the 2.6 is a tight fit already.

My 2.6 5-speed has plenty of power and I'm very happy with it. That would be an easy swap either as a whole engine with transmission or just transmission.

They are hard to find though, I have not seen a 5-speed in local junk yards at all.

If your 2.6 does not have enough power, I suspect it is not operating 100%.

Your temp issues appear to be electrical in nature, not mechanical. When you turn the heater on something regarding the cooling system must be malfunctioning or is given you false readings. Have you actually checked the coolant temp in the coolant tank to see if it is really spiking or do you have some sort of a grounding problem in which turning on the heater is causing an increase in the reading.

Is the temperature spike immediate, or does it take a a few minutes?
 
#3 ·
Thanks for the quick reply. The spike is gradual, which would be consistent with a mechanical problem. My mechanic did verify that I'm reading correctly, granted this was before I replaced the water pump.


As for the swap, yes I would be looking at the 24v. Plenty of people out there claim it does indeed fit. And yes, that gbx is going to be a tough find.
 
#4 ·
If gradual, then it must be still your fan not operating properly when the heater is turned on.
Perhaps the Dual Contact relay in the fuesbox is being effected negatively with turning on the core heater. Very strange. Good luck with that.

A 3.0L engine with 24V would be some serious power. Sounds like a lot of work though. Just a manual gearbox swap might make you happy if you can find one.
 
#5 ·
Thermostat.......at one point my car ran really cold on a winter night, so I replaced the thermostat and plastic cover.
A month or two later the thermostat cover broke while the car was sitting and wrecked the hood cover.....took hours to clean the mess.
Replaced it again, and started to notice when I parked the car......the coolant tank would pressure up......never overheated while driving, but seemed to heat up after I parked it.
I then bought the complete MB thermostat housing, fully installed with a new thermostat.......and that's still on the car. Works fine after this expensive part.
Head gasket.......I replaced my head gasket after my coolant light went on, and started sucking antifreeze into the engine. But there were weird engine sounds during very cold startups, and other minor cooling issues, 6 months earlier.

My recommendations, or experience......is that replacing the thermostat complete assembled housing helped "my" strange cooling issue.
Next....a failing head gasket can possibly go on for a long time causing nuisance issues before it lets go. My car ran great, even after it went bad. Unfortunately head gaskets are a common issue with our cars. But I didn't replace mine until it went "officially" bad.
 
#7 ·
Again thanks for all the feedback.

First off, thanks for the concern but fear not, a fresh thermostat came with the new water pump.

That fluid cap seems like an unlikely culprit. Rubber on it doesn't look bad and this car is a one owner that was garaged most of its life. However, I also only get the problem after a good stretch of driving/idling so the pressure/boiling scenario you describe is plausible. I do remember occasionally hearing a hissing sound when I've run it really hot and then switch off. I initially thought it could be a leaky heater monovalve, but this doesn't make sense since I'm not losing fluid. Unless the leak is at the monovalve, is large enough to cause the pressure problem, but is not large enough to cause substantial fluid loss. Next time I hear the hiss I'll double check that it's not the cap.

I did some more thinking and might be backing off the motor swap. Perhaps a head gasket, head machine, and vlavetrain rebuild will suffice. That is still going to cost a bit but then I'm basically guaranteed +250k miles and I'm sure to get a few horses back.

Also, it is very likely this entire overheating problem is some weird result of a head gasket reaching it's end. Bear in mind, I have a problem after a long enough drive either way, heat turned on or not. And Georgia summer is not going to be sensitive to the situation.

The 5 speed, however, is still on the cards. My mechanic gave me a lead on Benz restorers nearby that might know where to find a gbx.
 
#8 ·
So... i shall turn to this forum for some sage advice once more.

For those who have followed along, the overheating seems to be getting slightly worse. More frequently reaching near 120 at idle now. I'm worried if I don't act soon i can warp it or something.. is that a concern? I know these motors are supposedly bullet proof when taken care of but where are the limits?

My mechanic quoted me 2600 for a top end rebuild. Gaskets (incl. timing gasket and such) ... sending the top out to get machined and cleaned up. The kind of job that should see me through the next 150k miles.

It's a tough pill to swallow and it breaks the piggy bank wide open, but I don't really see a good alternative. Aside from a coworker suggesting I buy a junked motor and rebuild it myself on the cheap while I keep the current block running and then swap it out.

But I am a complete novice. Changing the radiator and water pump was the most extreme thing I'd ever done. This also assumes I can even find adequate work space which I don't really have at the moment. Also, my car seems likely to blow up before I accomplish anything on my own. We are heading into summer here.

What would you do?
 
#9 ·
Honestly, It is my belief that your overheating has nothing to do with your cylinder head gasket.
The only contribution from the head side could be that the water passages are blocked by gunk and rust.

Why do I think this is possible? A month ago I pulled a head from a 190E in the junkyard for future use.
It had 118K miles on it. I popped the valve cover and the cam/rockers/etc looked absolutely new and shiny.
Plugs looked clean. The car overall was clearly garaged all its life because all the plastic was new looking (I took the door handles) and the inside was also in great shape including the instrument panel. I took that too. Clearly the car was cared for from oil changes point of view but......

However, when I took the head off, I noticed that there was a lot of rust and gunk in the water passages. Same with the radiator hoses.
Clearly, even though the car was cared for, the coolant must no have never been flushed and the antifreeze was not the blue stuff. Maybe at some point it did not even have antifreeze in it so things must have rusted.

I took the head because I need the cam, rockers, maybe even valves for my head job soon. It was worth it for $56. A lot of labor though.

I can see a car like this overheating if the coolant flow is not enough due to blocked passages.
This is the only scenario I can imagine for your problem.

But in this case when you did the radiator and water pump you should have seen gunk and rust in there.
 
#10 ·
I've done oil analysis on most of my cars at some point from Blackstone labs. About $25 or $30, and the report will show wear metals and if coolant is entering the engine. They will also comment about what they think is going on, and whether or not the engine is any good.
I did an oil check...two oil changes after my head gasket replacement, and it showed clean of antifreeze...peace of mind insurance.
Years back I had a 92 Ford Escort wagon that was loosing a tiny bit of coolant. Oil analysis showed the coolant was getting in the engine, and later I found the intake manifold gasket was letting coolant through into "one" combustion chamber. Fixed it and all was well.
But the oil analysis showed that the engine was still good to repair.
One guy from work was complaining that his wife's Jeep was making noise. When I found out he was adding coolant, I told him to get an oil analysis...and it showed the engine destroying itself. He put a used engine in and all was better.
If oil analysis and coolant analysis of your "engine oil, and coolant" show good....then you can move forward with the cooling problem. But if it comes back bad...then plan B. Just an opinion.
 
#12 · (Edited)
This is a bit of a puzzle. A few points:

- A defective cap can encourage boil over at lower temperatures, but this is distinct from running hot. If you run hot, it's caused by something else.

- If a head gasket is causing this, there is some other telltale...you can test for exhaust gas mixed into the coolant, coolant mixed into engine oil, low compression, etc.

- If compression is low, the problem could be in the BOTTOM end.

- If the radiator was clogged, it's possible that the engine passages are clogged. You can try a citric acid flush to clean it out. But if it's really bad, mechanically brushing and cleaning those passages is a big deal.

- I have seen a case where crud settled in the lower radiator hose causing a blockage. The lower radiator hose can also collapse under suction if it's become soft.

- What happens when you turn on the heater? Hot water is drawn from the left rear corner of the head, circulates through the heater core and valve, and is returned directly to the water pump inlet via a pipe or hose on the right side of the block. This flow is accelerated by the electrical aux pump. It may vary with different engines and models, but it's the typical flow path. Since this flow bypasses the radiator, it can be quite warm. But if the thermostat passage is operating correctly, it's blended with cool water coming back from the radiator. So likely the lower hose or thermostat compromised. Or your radiator is clogged yet again.

Given all of this, before you spring for an expensive engine job, take a chance and replace the thermostat and lower hose again. And have your new radiator flow tested at a radiator shop. Thermostats can be bad right out of the box, so don't get hung up on the one you just installed. Test the new thermostat in a pot of boiling water before you install. If none of this fixes the problem, you're looking at a bigger engine problem.
 
#13 ·
One more point...replaced water pump. The most critical part affecting flow is the water pump impeller. You need the largest diameter impeller that will fit in the involute. It's not unheard of for a rebuilder to replace a damaged impeller with one that's too small. In that case, you have a fan stirring coolant around, rather than a pump. So that's something else to think about.
 
#14 ·
Thanks all for the in-depth responses. Your explanations are helping everything make sense.

I did check the other day and notice my radiator is cool on one side. Just like the old one was when I decided to replace it. There HAS to be a flow problem and it would make sense that I have rust or some other gunk coming from somewhere because just after each individual coolant component (water pump... radiator) the temps were fine for a while and gradually rose again. Probably just the coolant flush that temporarily mitigated the buildup. Makes a lot of sense that turning on the heat then spikes the thermostat because there is very little cool fluid coming from the radiator to mix with it.

The water pump was brand new, so it should not have been a shoddy rebuilt part. However, I wouldn't be surprised if it's taken some damage just from running under these stressful conditions. I've driven easily over 6k miles since replacing it.

I would have loved to poke and prod, but unfortunately this car is my daily driver and I need it to be running properly, and I don't have the equipment or expertise (or time at the moment) to do what's necessary myself. I have basically decided to do the head gasket and valve train regardless. My mechanic pointed out a small oil leak when inspecting before I even bought it, so I knew a big expensive engine job was going to happen eventually.

I will report back with any information that comes out of this little box of mystery.
 
#16 ·
Where is the cold spot on your radiator. Is it on the drivers side or the passenger side. How close is it to the thermostat housing.

Also there are two sure fire ways to tell if you have a head gasket problem. There is a chemical liquid test where you have blue fluid in a special tube inserted into the top of your coolant reservoir, and it will turn yellow if there are exhaust gases present in the exhaust. The other way is the oil analysis others have addressed in this thread already.

Do not have the head pulled without results from either test unless if you have coolant pissing out of the mating zone between the block and head unless if your mechanic is so sure that it is the head that he will guarantee it as the solution to your problem (which means he'll eat the 2600 if that doesn't fix the issue).

If I were you, I'd take the thermostat out while the car is cold, and put it in a pot of boiling water to see what it does. Then see if you can actuate the thermostat with your fingers (you shouldn't be able to).

I doubt your car has a clogged cooling system, unless if you bought a $400 heap that happens to be a thousand times worse than my shitheap.
 
#15 ·
Sorry Mezzari88 but I disagree with your mechanic. One pulls the head to fix oil or coolant leakage issues or fix valves that can not hold compression or fix valve guides that cause oil leaking into the cylinders and burn or even change rockers or a camshaft that is worn. Notice these are all mechanical issues.

It is extremely unusual to pull the head because of your overheating problem and there is suspicion that there is a coolant flow problem in the head.

Has a complete coolant flush been performed on your car in which you can tell what might be blocked?

You can force water thru the thermostat hose and see if it is flowing nicely from the hose connected to the engine block.
If it is, I do not see how your cylinder head is the culprit. You can even take off the coolant temp sensor to see if there is good flow there. Actually I would advise this. All this can be done in an hour by a competent mechanic.

This is a very cheap operation as opposed to pulling the head off. That is a big operation. Now you're talking about a minimum of a 8 hour job and it has risks associated with it.
 
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