I was sitting in a parking lot today on the phone chatting with my boss and all of a sudden i hear a *ding* and notice that my water temp had just creeped into the red! I shut it off and go inside for about an hour and come back out, drive it about a half mile to pick up some coolant(i figured that was the issue) and back.. i noticed while driving it that it warmed up as usual but then started moving fast towards the red, then back to half, then back towards red and back to half, all in about a mile of driving. I get home and check the coolant and it seems to be just fine??? I then check the fan, and it's running as well so I just let the car sit for a while to get totally cold. I came back to it and fired it up and just let it idle for a while while watching the gauge.. It started out cold, eventually went to half, creeped a bit over and then sat there for about 3 minutes until it started moving pretty quick to the red. Once it got close it went right back down towards the half again :confused


Does this sound like a problem with temps or could it be sensor? I would think if a sensor went bad, it wouldnt read right at all???

I've never seen a bad sensor exhibit that behaviour. But I have seen a bad head gasket do exactly that... I hope that's not what it is.

I've never seen a bad sensor exhibit that behaviour. But I have seen a bad head gasket do exactly that... I hope that's not what it is.


what would be signs that it would be the head gasket?? It hasnt been throwing any white smoke out the exhaust or idling anything other than normal?

you should look out for a creamy looking substance in the oil or oil in the header tank of the coolant system if you have the tools availible to you, you might want to consider doing a compression test on the cylinders. my old 535 temps did the exact same thing i later found out it was the head gasket if the gasket has failed you need to get it fixed asap as it can become a fatal issue

I blew a head gasket in my e36 and had that EXACT same problem

A small head gasket leak, that only allows air to be pumped into the cooling system may produce no symptoms other than random overheats, possibly accompanied by an inexplicable loss of coolant. What happens there is that an air bubble forms in the block and while that's happening the cooling system pressure is rising. At some point the pressure gets high enough for the cap to lift, which vents the excess pressure. If enough air manages to work it's way to the cap before the pressure gets too high there'll be no loss of coolant. Otherwise some coolant may be lost when the cap lifts.

A qualitative check for this is to do a complete bleed of the cooling system. If while trying to bleed the systemyou can't seem to ever get all of the air out the odds are that it is being continously pumped in when the engine is running. If you do manage to get a full bleed, check to see if you can bleed more out after the engine shows a hotter than normal condition.

The definitive test is to pressurize each cylinder with 150-180psi for several minutes while monitoring cooling system pressure with a sensitive gage. A rise in cooling system pressure indicates a head or head gasket problem. If this test yields negative results on a cold engine it should be repeated on a hot engine.

thanks for all the help guys, the car has over 222K on it now so it's entirely possible.. What am i looking at to have a shop do a head gasket on this car?? It might almost be cheaper to get a more fresh 535i or maybe another motor that would be an easy swap.

I sure hope it's not the head gasket, this would be terrible timing :(

Also, I checked the Oil and that seems normal. Levels are fine and no milkiness. The oil cap also looked fine. Wouldnt i have some kind of milky oil if it was just starting to go bad?

Seal problems (cracked head, cracked block, or head gasket failure) come in four forms:

1) A leak between a cooling passage and a cylinder. Depending on the severity, this can just result in air being pumped into the cooling system, or it can be bad enough that coolant enters the cylinder and results in dense clouds of white smoke from the exhaust.

2) A leak between a cooling passage and an oil gallery. This results in coolant mixing with oil and forming a milky emulsion in the oil.

3) A leak between cylinders. This causes compression loss and frequently results in misfires.

4) A leak between a cylinder and an oil gallery. This will cause excessive oil consumption as a result of over pressure in the crank case. In extreme cases it can caus oil to enter the cylinder and result in blue smoke from the exhaust.

(1) seems to be the most common on a BMW with (2) being the next most common.

The exact cost of a head gasket repair will vary according to what's happened (just a gasket, warped head/block, or cracked head/block) and what other parts need to be replaced or repaired (timing chain, valve seals, valves, etc). I would guess somewhere around $1600 to $2000 on an M30 if the head & block are okay. At 225K on the engine, I'd look into a lower mileage used engine. That would probabaly be more expensive, but not by a lot.

Seal problems (cracked head, cracked block, or head gasket failure) come in four forms:

1) A leak between a cooling passage and a cylinder. Depending on the severity, this can just result in air being pumped into the cooling system, or it can be bad enough that coolant enters the cylinder and results in dense clouds of white smoke from the exhaust.

2) A leak between a cooling passage and an oil gallery. This results in coolant mixing with oil and forming a milky emulsion in the oil.

3) A leak between cylinders. This causes compression loss and frequently results in misfires.

4) A leak between a cylinder and an oil gallery. This will cause excessive oil consumption as a result of over pressure in the crank case. In extreme cases it can caus oil to enter the cylinder and result in blue smoke from the exhaust.

(1) seems to be the most common on a BMW with (2) being the next most common.

The exact cost of a head gasket repair will vary according to what's happened (just a gasket, warped head/block, or cracked head/block) and what other parts need to be replaced or repaired (timing chain, valve seals, valves, etc). I would guess somewhere around $1600 to $2000 on an M30 if the head & block are okay. At 225K on the engine, I'd look into a lower mileage used engine. That would probabaly be more expensive, but not by a lot.



thanks for all your input, I havent driven the car since and don't plan to until i get can get it to a shop to investigate further. Besides the M30, what is a decent swap for this car??

There are a number of engines that could be swapped in, but the least expensive is going to be another M30B35

It really sounds to me like it's just a bad thermostat. I'd check that as it's an easy fix as compared to a headgasket replacement.

It really sounds to me like it's just a bad thermostat. I'd check that as it's an easy fix as compared to a headgasket replacement.

omg... an aussie!

and yea it sounds like a head gasket.. but if the oils not milky etc... i got no idea

*that post was really just to aknowledge an australian lol

Well it's in the shop now, i'm just waiting on the verdict!


Pray for a thermostat :help

Well it's in the shop now, i'm just waiting on the verdict!


Pray for a thermostat :help

What did it turn out to be?

if its jumping like crazy theres probly just air in the system. These cars are a bitch to bleed completely and take forever. If you can elevate the back end as much as possible and bleed the crap out of it for a solid half hour. Your expansion tank might a a crack in it and be the cause of some extra air in the system. Try it out, its the cheapest fix offered so far.

My 93 525 is doing the same thing. Just bought it for $900 knowing that it was over heating. If it turns out to be the head gasket I will just do it myself. I know it needs a thermostat. The thermostat is stuck closed. The lower hose never gets hot. I hope the thermostat will fix all the problems.

Did you ever find out what is wrong with your car?