Overheating Problem- ongoing for about 1 year- HELP

fatboycowen · 01-17-2008, 05:25 PM

I have posted on bimmerforums about this problem, but still cant find the problem or a solution. I'l try to tell the story as completely as possible.
Car: 1998 BMW M3 US

About 2 years ago, i replaced my entire cooling system during the winter offseason. Radiator, waterpump, thermostat, thermostat housing, radiator hoses, etc. I also replaced the belt driven fan with a spal fan. I autocross very frequently, and the car ran great. About halftway through the following summer, the car overheated going up a big hill during the hot summer. Turns out that the Spal fan was defective and it stopped working when it was hot. The car went just into the red before i shut it off. I waited for it to cool, then drove it home and replaced the Spal fan (warrantee). After that, the car ran great again for the rest of the summer, including many autocrosses.

During the next winter, i did some suspension stuff and only changed the oil and coolant. Of course i bled the coolant throroughly as usual. The car ran great on the street, as normal. However, at the first autocross of the season (april), the car's temp gauge moved past 1/2 just after the 3rd autocross run. Fan was working, etc. I took the cooling system apart and checked everything, flushed the new radiator, etc, and put it back togather and re-bled. Next autocross, same result- overheat (shut off after the gauge moved past 1/2 - didnt get in red). Took the cooling system apart again, tested the thermostat on the stove, etc. Same result- overheating.

So, on the advice of the forums and from reading, i removed the head (myself with the help of the Pelican article. The head gasket didnt look bad. Couldnt really see signs of leakage. Took the head to a local machine shop. They pressure tested and couldnt find any leaks. They found that it was warped, and decked the head. I replaced all the gaskets and the head bolts. Put the head back on, timed everything, etc. The job went flawlessly. The car started right up and ran great on the street. First autocross after the fix, same result, overheat.

Then, i replaced the coolant expansion tank and cap as well as the smaller hoses which lead to the block and the tiny hose which goes through the fan shroud to the exp. tank. I also installed an aftermarket gauge with a sensor in the thermostat housing. Autocrossed the car again, same result, overheat. This time i confirmed that the factory gauge was correct. The needle moved past 1/2 at about 230 degrees.

More reading and asking, and some suggestions that the head might still be cracked, and the pressure test wasnt good enough. So, i pulled the head again (this past November) and brought it to a reputable machine shop that has lots of experience with these heads (different shop). Their contention is that the pressure test should be 100% accurate. They pressure tested it and it passed. They then took it apart and inspected it, and performed whatever tests they do, and called me back with the bad news. They said they couldnt find a problem. They said the head was in excelent shape and there is no way the problem was caused by this head.

Next, i borrowed a straight edge from a friend and bought a feeler gauge. I just put it on the block (after cleaning it). The center of the block is very slightly lower then then ends by about .0015 to .002 inches (lengthwise). This shows up when the straight edge is straignt and in a diagonal fashion. From what i have read, this is within spec and should be ok. So, here i am.

Where do i go from here? Part of me wants to sell the car. Unfortunatly, i love the car too much. I am almost tempted to just cut my losses and buy a used engine (got a quote- $3800 shipped from bavarian engine exchange). What would you do. Please help.

Thanks for reading.

Jon

Jeron · Jeron's Garage

I am having a similar problem.

I didn't overheat but I pulled the head for another reason. I had had it checked and milled very slightly. Since then I have been overheating at the track.

My first overheat was because I left the clamp off the small top hose at the expansion tank and the hose came off, I lost coolant and it got hot, not on the track but at idle. I repaired it.

Then the next couple of track weekends I continued to have the same problem where the car car overheated after coming off the track. When I would shut the engine off the head temp would boil my water and it spilled onto the ground. The reason turned out to be that I had a small leak and I was getting air into the system. The leak is at the hose connected to the throttle body. I think I didn't install the clamp tight enough. I haven't fixed it but will before the season starts.

Anyway, on to your problem. You are AX-ing so you hit the "pits" every 60 seconds. Is yours overheating on the course or only in the pits? Does reving the engine drop the shown temp? Have you measured the top radiator hose or thermo housing temperature with a pyrometer?

fatboycowen · 01-18-2008, 05:25 AM

Quote:

Originally Posted by Jeron

Anyway, on to your problem. You are AX-ing so you hit the "pits" every 60 seconds. Is yours overheating on the course or only in the pits? Does reving the engine drop the shown temp? Have you measured the top radiator hose or thermo housing temperature with a pyrometer?

The overheating is any time. In some cases, the car will overheat after just arriving in the pits after a run. In other cases, if i watch the gauge carefully (always now), it will creep up during a run. I cant seem to find any reasoning. Revving the engine does not seem to drop the temp. I have not measured the top hose, but i can tell you it gets HOT! It also gets prety hard. I know that the thermostat is opening, because as the temp rises, the top hose builds some pressure and gets hot.

Jeron · Jeron's Garage

#1 is always make sure there is no air in the system
I assume since you have spent this much time on it that you are sure about that.

During normal driving the engine stays at TDC? Once warm, the heater gives good heat and never blows cold? You are running coolant and not straight water?

If there is no air and no leaks in the system and its overheating at speed (so sufficient airflow) then it must be too little coolant is circulating to the radiator.

Water pump, radiator and thermostat are new. That leaves two thing I can think of:

1) restriction, a piece of debris in the block, hose or radiator
2) belt slip, the belt tensioner is bad and it lets the belt slip at high rpm so the water pump isnt turning

fatboycowen · 01-18-2008, 09:31 AM

Quote:

Originally Posted by Jeron

#1 is always make sure there is no air in the system
I assume since you have spent this much time on it that you are sure about that.

During normal driving the engine stays at TDC? Once warm, the heater gives good heat and never blows cold? You are running coolant and not straight water?

If there is no air and no leaks in the system and its overheating at speed (so sufficient airflow) then it must be too little coolant is circulating to the radiator.

Water pump, radiator and thermostat are new. That leaves two thing I can think of:

1) restriction, a piece of debris in the block, hose or radiator
2) belt slip, the belt tensioner is bad and it lets the belt slip at high rpm so the water pump isnt turning

I have followed a number of different bleed procedures, with the same results. I usually bleed 3-4 days in a row after opening the system.

The engine is moving, therefore it cant be at TDC all the time, only for an instance. I assume you mean the Temp needle. Yes, it stays straight up. During even the hardest street driving (trying to make it overheat), the highest i can get is 210 maybe 215 on the aftermarket gauge, but it goes down quickly. The heater always blows hot, never cool. I have tried water only with water wetter, 50/50, etc. all with the same result.

Autocross is somewhat slow speeds (2nd gear, maybe 3rd sometimes)...

#1 Above cant be in a hose, as i have flushed all the hoses running to the radiator. I cant comment about the block. However, during each of the teardowns, i hooked the garden hose up to a radiator hose and let it flush out. It pushes out very fast, so i dont suspect a blockage in the block. However, i dont know if my procedure is perfect. What could be causing the blockage? I never had a plastic impeller. I never had my radiator break, etc. Is there some way to test flow? I can tell you the radiator is SUPER HOT when the car is hot. Although, i didnt put a pyrometer to it.

#2 above is a posibility i had thought of. I checked the belt several times. No signs of slippage. Also, the belt seems tight to me. I dont know how tight it should be, but it seems tight.

Unfortunatly, i cant go test these items now, if it means having a complete engine. As i said earlier, the head is taken apart at the shop waiting my instructions.

Thanks for the help so far.

Jeron · Jeron's Garage

Yes, TDC I meant engine temp.

Blockage is rare but would be plastic impeller bits or sludge. YM98 is after the bad plastic impeller era so its doubtful.

Something I didn't mention along the lines of the belt slippage is a bad water pump. Since the head is off go ahead and pull the pump and make sure the impeller and input flange are as one.

I thought this thread might help you but I doubt it:
94 525i need help

You should be checking the temperature of the bottom hose. The top (rad inlet) hose will get hot even if there is a a bad thermostat or circulation problem.

It's too late now but I don't see any reason why you needed to pull the head either time.

fatboycowen · 01-18-2008, 11:46 AM

Quote:

Originally Posted by Jeron

Yes, TDC I meant engine temp.

Blockage is rare but would be plastic impeller bits or sludge. YM98 is after the bad plastic impeller era so its doubtful.

Something I didn't mention along the lines of the belt slippage is a bad water pump. Since the head is off go ahead and pull the pump and make sure the impeller and input flange are as one.

I thought this thread might help you but I doubt it:
94 525i need help

You should be checking the temperature of the bottom hose. The top (rad inlet) hose will get hot even if there is a a bad thermostat or circulation problem.

It's too late now but I don't see any reason why you needed to pull the head either time.

Based on how the head looked (CLEAN), sludge is very doubtfull.

I replaced the water pump again with a steward HP water pump after the problem started, it didnt help.

The bottom hose was hot to the touch as well, i remember checking several times.

I appreciate your opinion, but i removed, flushed, inspected and replaced the entire cooling system several times during all this (before pulling the head). I didnt know what else to do. I read many older threads on bimmerforums that mimicked my problems or came very close and ended up being a head gasket or cracked head.

Jeron · Jeron's Garage

I agree you can rule out sludge. You have a new radiator and you would have noticed it during all of you work.

A second water pump, a Stewart no less, should eliminate the bad pump idea.

Your radiator has enough capacity to cool the engine as long as it gets sufficient air flow. So once you get it running again see if the radiator temperature (pyrometer) is as nearly high as the engine temp. If the radiator outlet temp is cool then it must be circulation. If the radiator outlet is hot then it is fully heat soaked and the engine must be generating a tremendous amount of heat. I can only image clogged cats or very very lean (but that would show on the plugs.)

Let me know how it goes. I know it can be frustrating.

fatboycowen · 01-18-2008, 12:23 PM

Quote:

Originally Posted by Jeron

I agree you can rule out sludge. You have a new radiator and you would have noticed it during all of you work.

A second water pump, a Stewart no less, should eliminate the bad pump idea.

Your radiator has enough capacity to cool the engine as long as it gets sufficient air flow. So once you get it running again see if the radiator temperature (pyrometer) is as nearly high as the engine temp. If the radiator outlet temp is cool then it must be circulation. If the radiator outlet is hot then it is fully heat soaked and the engine must be generating a tremendous amount of heat. I can only image clogged cats or very very lean (but that would show on the plugs.)

Let me know how it goes. I know it can be frustrating.

I thought about the lean condition. The car uses stock software, etc. Only modification is Cold Air Intake. I also had RC engineering clean the injectors when i had the head out the first time.... I only recently thought about clogged Cats. Is there any way to test for this? Wouldnt the car run crappy? The car runs great. I do sometimes get a stumble at about 5k rpm, but there was a recent thread about this on bimmerforums, and it seems to happen to a ton of people....

Once my machine shop tells me how much it will cost to reasemble the head, i will make my decision what to do. Speaking of which: Would you replave the springs/retainers on a 98 S52 with about 94k miles? He said he usually does automatically. He also mentioned that this was one of the only BMW heads he has seen that doesnt need exhaust guides at this milage...

Jeron · Jeron's Garage

I would expect bad cats to cause it to run low on power at high RPM. I think you would notice but a dyno should show it and it should include a sniffer to show you a lean condition. I don't know if I would trust the dyno air/fuel ratio though because all of the dynos a/f at our last event showed lean. I did some inconclusive research and the best guess was the a/f needs to be taken precat.

Another lean possibility would be pump, filter or pressure regulator. (I'm sure you realize we are grasping straws at this point.)

At 115k, I replaced valve seals, one cracked collet (valve retainer) and a spring seat (missing from the factory.) The shop said all the springs tested fine and even strength and did not recomend replacing them. My bill, head without cams, was $50 to mill and $250 for pressure, grind valves, grind valve seats, new valve seals.

I'm debating supercharger vs LS1V8. If I go supercharger I may wish I went with springs but I doubt it. I would only replace springs if I went with a stiffer spring (aftermarket). If you put in performance cams you will probably want stiffer springs.

I did put in ARP head studs but I got them half price so it was nearly a no brainer.

fatboycowen · 01-21-2008, 05:07 AM

Quote:

Originally Posted by Jeron

I would expect bad cats to cause it to run low on power at high RPM. I think you would notice but a dyno should show it and it should include a sniffer to show you a lean condition. I don't know if I would trust the dyno air/fuel ratio though because all of the dynos a/f at our last event showed lean. I did some inconclusive research and the best guess was the a/f needs to be taken precat.

Another lean possibility would be pump, filter or pressure regulator. (I'm sure you realize we are grasping straws at this point.)

At 115k, I replaced valve seals, one cracked collet (valve retainer) and a spring seat (missing from the factory.) The shop said all the springs tested fine and even strength and did not recomend replacing them. My bill, head without cams, was $50 to mill and $250 for pressure, grind valves, grind valve seats, new valve seals.

I'm debating supercharger vs LS1V8. If I go supercharger I may wish I went with springs but I doubt it. I would only replace springs if I went with a stiffer spring (aftermarket). If you put in performance cams you will probably want stiffer springs.

I did put in ARP head studs but I got them half price so it was nearly a no brainer.

I appreciate the great info Jeron. I had a feeling the springs and retainers wouldnt be required. I am not really looking into cams at this time, and dont forsee myself in the future. The LS1 conversion has certainly crossed my mind, but i dont have the money for that.

Let me ask you this, regarding the head studs. I havnt done any measuring, but when installing the head with the studs, i would assume the studs go into the block first, then the head drops down over them. The wiring harness is rather close to the top of the back of the head. Does this get in the way even more with the studs there?

Thanks again.

Jeron · Jeron's Garage

Yes, you have to install the back two studs (or was it four) after the head is in place. Also I think you should lube between the washer and nut. Mine made a horrible creaking noise (from the friction at max torque) and I think it the lube there would help get accurate torque values.

fatboycowen · 01-22-2008, 05:07 AM

Well, with more research on bimmerforums, it has been suggested that i pickup a good, bare, used cylinder head, and have my shop redo that one instead. They contend that the pressure test doesnt always find leaks, and even die testing can sometimes miss leaks if they are in tough to see places. Especially since i am in this position with the current head taken apart.

Jeron · Jeron's Garage

I hope it works out, let me know.