Fluctuating coolant temp. M20B25

[Kepes 231]

Hi team,

My pfl 325i E30 has been having cooling issues since I replaced the head gasket at christmas time last year. Before this I had no issues.

Quite simply, the temperature gauge rises when at idle or when under load for long periods (hills, driving hard, etc). The fluctuation goes from just below halfway on the gauge to just about the 3/4 mark or whenever I decide to turn on the heaters in the situations mentioned above.

I thought it was the fan clutch, so I replaced that... 3 times. 2 were used units and the one in there now is brand new OEM.
The thermostat is 1 year old.
Waterpump done with head gasket

I had no issues before doing the head gasket so I don't suspect radiator

I had a thought the other day that perhaps it could be the ignition timing, too advanced perhaps? The timing belt was changed with the head gasket by me, and it was my first time doing it.

The engine did ping after the work mentioned, I thought that the skimmed head had raised the compression enough to cause that and 'fixed' it by using premium gas

Could a few degrees out cause the engine to overheat in the situations mentioned?

Blasting the heaters keeps me out of trouble and is easy to put up with in the winter but summer is a different story!
Thanks for any insight! :~)

Edited September 4, 2015 by Kepes

[charles28 136]

I had this issue with one of my E30's, however in my case it was the radiator, (Head gasket had also been done before hand).

Going up hills would result in the temp going over 1/2 way, i also replaced the fan clutch, thermostat etc first.

[Kepes 231]

I had this issue with one of my E30's, however in my case it was the radiator, (Head gasket had also been done before hand).

Going up hills would result in the temp going over 1/2 way, i also replaced the fan clutch, thermostat etc first.

Hmmm.. good to know. Perhaps I should not completely disregard the radiator as being a suspect... Fins and everything appear to be fine. Will take it to a radiator shop to be flushed next week

edit: I take it you replaced the radiator and the issue went away?

Edited September 4, 2015 by Kepes

[Ahmedsinc 414]

Possible that one of the end tanks has slightly lifted away from the rad core or has a hairline split. Noticed any coolant loss at all? If you do replace the radiator do the hoses at the same time, one weak spot on a hose can cause all sorts of dramas

[Kepes 231]

Possible that one of the end tanks has slightly lifted away from the rad core or has a hairline split. Noticed any coolant loss at all? If you do replace the radiator do the hoses at the same time, one weak spot on a hose can cause all sorts of dramas

Funny you say that because I have noticed some coolant loss. Not much at all but definitely enough to notice. What are the end tanks?

Worth noting that the radiator is not original, not sure when it was replaced but most likely previous owner. Doesn't look more than a few years old but I could be wrong.

[Ahmedsinc 414]

The plastic caps on left and right sides of the radiator. Held in place by little ali tabs on the radiator core. Odds are you probably pressurised the cooling system when the head gasket sh*t itself, not enough to blow the rad apart but enough to create some little cracks. The plastic also degrades with heat cycles and age, becomes brittle and fails, leaving you on the side of the road surrounded by a big steamy puddle.

Get a leak down test done, and replace the cooler before its too late.

[_ethrty-Andy_ 2132]

i **think** i have a 6 cylinder E30 radiator in the shed, though yours might be different being a prefacelift.

[Ahmedsinc 414]

Personally I'd replace it with an all alloy race style item or go new OEM. Pelican parts have them for way cheaper than the local stealers ( I paid $300 incl shipping for a BMW branded Behr one compared to the $700+ I was quoted by Team McM) and are usually at your door within 7 days of ordering.

Maybe your local dealership will take pity but I doubt it.

[e30ftw 410]

If someone was using headgasket sealer crap in the coolant before you ended up with it and the issues, it can clog up the radiator. Pays to give it a good flush, or just swap it.

[charles28 136]

Hmmm.. good to know. Perhaps I should not completely disregard the radiator as being a suspect... Fins and everything appear to be fine. Will take it to a radiator shop to be flushed next week

edit: I take it you replaced the radiator and the issue went away?

Yes, it fixed it straight away, the old radiator looked ok on the outside too, but inside had started to collapse internally, perhaps due to too much pressure from the headgasket going.

[Allanw 1071]

Why did the head gasket blow anyway?

Fan clutch won't affect hill climbing - it's really only for idling in traffic... and even then, ONLY if the radiator radiates enough heat to heat up the thermostat on the clutch.

If the temp is climbing on hills, it means the engine is making more heat than the cooling system can dispose of - most common cause is either lack of airflow (not a problem if the car is moving) or a radiator that either isn't flowing enough (clogged/blocked), or can't get the heat from the coolant to the outside world (internally coated with crap or that dodgy stop leak stuff).

If the headgasket cause is unknown, then good practice is a cooling system overhaul, or at least a thorough inspection, including the radiator.

I'd not bother taking the radiator to a shop, when that money can go directly towards a new radiator. The really only effective way of cleaning a radiator, is to remove the tanks, and "rod it out", which isn't cheap or easy - The '29 Ford cost $400 bucks to open and clean out. (but a replacement costs a lot more than an E30 one!)

[hotwire 352]

As Allan alludes to - most likely a flow problem & that likely to be radiator. That case reinforced by the fact that opening the heater tap helps the issue - allows more cooling effect via the heater core.

I would though - get the radiator checked - a radiator specialist will be able to confirm if flow is a problem in it. Otherwise it is replacing on a whim.

You need to also confirm - where is the water loss going to? Is there an external leak - you will be able to see it. I assume you are running antifreeze?

Otherwise - leaking heater core - check carpets. Pressure test the cooling system.

If no external leak then you likely still have an engine issue - water through combustion. Coolant level should not decrease at all. If it is - its going somewhere.

[Kepes 231]

Thanks for all of the replies guys. I really appreciate it.

The headgasket blew on the previous owner. I didn't know this when i bought the car. The glittery head gasket seal stuff from repco they had used let go after about 9months of me owning it. Apparently the stuff hardens/seals when it comes in contact with air, so perhaps when i took the cooling system apart and introduced air into the system it caused a clog in the radiator.

Sounds like radiator will be the first place to start, I'll get that checked out by a shop and go from there.

As for replacing the radiator, I'm having a hard time finding any sort of part number or anything that looks similar to it's design (hose/inlet/outlet placing) on pelican parts and other online stores, but I'll leave or that for when/if the radiator shop says it should be replaced. edit: RealOEM do not list a part number for my radiator either. I'll get pictures tomorrow.

I will look deeper into where this coolant is going, thanks for the suggestion. Yes, I am running antifreeze. Not BMW coolant, but prestone coolant. Could this be an issue?

Edited September 6, 2015 by Kepes

[hotwire 352]

Any decent radiator specialist will be able to confirm if it is at fault or not, hence why I say - get it checked to confirm.

As far as replacement (if required) get a price from the radiator guy - it may well not be worth your while trying to source your own.

Anti freeze, BMW product is best but Prestone is quite ok. The local radiator repairer here is really on to it & he uses Prestone. Be aware - there is crap stuff out there & does more harm than good.

Yes it is a must to use inhibitor but I was more referring to the point that if an external leak - it should be visable

[Kepes 231]

update: Flushed the cooling system with some off the shelf stuff from supercheap auto. Not the best way to flush it I know, but it seemed to have worked pretty well.

There was a bit of 'glitter' that is the headgasket seal in a can which came out in the flush and the engine now operates at a lower temperature according to the gauge.

Temperature still does climb in traffic, however it doesn't pass the 1/2 way mark like it used to, and like I said when cruising the temperature isn't as high as it was previously.

New fan too, as the old one was hitting one of the coolant hoses. Much better, no more wobble to it.

When I next go to flush the cooling system I will invest in a new radiator

Thanks for all the help team!

[Ahmedsinc 414]

Well, that ought to delay the problem for a couple of weeks at least!

[Kepes 231]

she'll be right

[hotwire 352]

Seriously, I would get the radiator professionally checked.

Also, have you determined the water consumption issue? - External leak?

If not external - you will still have an engine issue. - It should use NO water

[_ethrty-Andy_ 2132]

she'll be right

Thats the spirit

Seriously, I would get the radiator professionally checked.

Also, have you determined the water consumption issue? - External leak?

If not external - you will still have an engine issue. - It should use NO water

This though.

tbh at 30 years old a new radiator can only be a good thing in any case.

[Kepes 231]

Seriously, I would get the radiator professionally checked.

Also, have you determined the water consumption issue? - External leak?

If not external - you will still have an engine issue. - It should use NO water

I 100% agree with you. However as a student funding flight school I can't really get this car 'perfect' at the moment. It will happen eventually :~)

For now, the car doesn't get hot enough to cause any major engine damage so it'll do.

As for the coolant loss, I can pretty much guarantee it will be external. All the hoses etc are original (bar one). The head has been pressure checked and resurfaced, and the block is not warped.

[B.M.W Ltd 950]

I 100% agree with you. However as a student funding flight school I can't really get this car 'perfect' at the moment. It will happen eventually :~)

For now, the car doesn't get hot enough to cause any major engine damage so it'll do.

As for the coolant loss, I can pretty much guarantee it will be external. All the hoses etc are original (bar one). The head has been pressure checked and resurfaced, and the block is not warped.

How closely did you inspect the block for cracks and corrosion ? M20 blocks are well known for cracking

[e30ftw 410]

Wait til it's summer and it gets warmer, Probably get worse.

Radiators are real cheap for OEM replacement ones through FCPEuro. I picked up a new one with a whole lot of other stuff and it was $80 shipped.

[Kepes 231]

How closely did you inspect the block for cracks and corrosion ? M20 blocks are well known for cracking

Very closely, I waited about a week to get the head back so I had plenty of time to look over the block.

Wait til it's summer and it gets warmer, Probably get worse.

Radiators are real cheap for OEM replacement ones through FCPEuro. I picked up a new one with a whole lot of other stuff and it was $80 shipped.

Yeah no doubt, I lived with it last summer so can so again this summer.

Not so easy (or cheap!) for me as my radiator is either not very common or not on US E30s at all because none of the US sites stock it. Only place I could find it online was schmiedmann. $300NZD shipped. Not sure how you managed to get one for $80 shipped. The cheapest one they have listed atm is $143 usd

[_ethrty-Andy_ 2132]

Very closely, I waited about a week to get the head back so I had plenty of time to look over the block.

Yeah no doubt, I lived with it last summer so can so again this summer.

Not so easy (or cheap!) for me as my radiator is either not very common or not on US E30s at all because none of the US sites stock it. Only place I could find it online was schmiedmann. $300NZD shipped. Not sure how you managed to get one for $80 shipped. The cheapest one they have listed atm is $143 usd

are you searching under 325e?

[will 169]

Head/block cracks will often not show up under standard testing - they only start leaking when the engine gets hot and under pressure. The one sure fire way to find most of these minor leaks is to use a fluro dye in the coolant, take it for a hard run and then use a UV light around the outside and in the rocker area to detect the presence of the dye leaking out.

Cracks in the internal combustion area are more difficult to determine, but usually they will leave traces on the spark plugs.. but you need to be experienced in reading plugs to detect small coolant leaks into the combustion area. Standard pressure testing often does not detect these small leaks as the pressure used is insufficient to push fluid out of the crack.

Testing the coolant for the presence of exhaust gases is another way of determining if the crack is between the combustion/coolant areas.

A leak-down cylinder test will also sometimes show up a leak as the pressures used in the test are far higher than the standard cooling system test pressures. You will get a pressure build up in the cooling system which can be detected by a pressure gauge installed in the cooling system. You might also get an audible hiss inside the system.

An easy way to check if your radiator is partially blocked is to use a non-contact infra-red thermometer. Get the engine up to operating temperature and then aim the device at various spots across the face of the radiator (back and front) and note the readings, compare these to readings obtained off the lower and upper hoses. For a radiator to function effectively, it should have reasonably even temperatures across the face at the same horizontal level (assuming vertical tubes) with temperatures hot at the inlet side in line with the hose temp, and cooler at the outlet in line with the outlet hose temp.