Overheating M20B25

[Grrrmachine]

Started using the E30 for a daily commute in city traffic, and she does NOT like idling at a standstill for 20 mins - the temps really creep up. It doesn't help that the temp gauge is a bid odd; once the needle approaches the 3/4 mark, it starts flickering around wildly and only settles down when the temps come back to 1/2.

I've been told M20 engines should sit near the 1/4 temp mark, but both this engine and the previous M20B20 in the car sat at 1/2 or just over on a motorway run. This engine has had a new waterpump, new coolant hoses, a new tropical rad (because there's aircon) and a new instrument cluster in the past year, along with fresh coolant, so none of that could be the issue.

Is this likely just to be a bleeding issue, or could my thermostat/viscous fan be on the way out?

[BenHar]

Viscous fan.

Ben

[mcbonio]

Temp needle should sit at 12 o'clock chap, as it's overheating in traffic and cooling down when in motion I'd say viscous fan clutch is goosed.

When heated up try and stop it with a newspaper, it should be locked hard and be unstoppable. If you can stop it then it needs changing.

[jmc330i]

http://www.e30zone.net/e30zonewiki/inde ... ooling#Fan

My M20 has always sat at the 1/4 mark, only moving towards 3/4 in stop start traffic, but wouldn't go over 3/4.

[Grrrmachine]

mcbonio, you cheeky coont

It got me thinking because someone posted earlier this week that M20s should sit solid at the 1/4 mark when driving, and neither of mine ever did.

[Brianmoooore]

Temp needle should sit at 12 o'clock chap, as it's overheating in traffic and cooling down when in motion I'd say viscous fan clutch is goosed.

Should be at 1/4 (just over) on a M20, half way on a M40.
If revving the engine when the needle has reached 3/4 doesn't produce a noise like a prop. driven aircraft on its take off run, then the viscous coupling isn't engaging.

[Grrrmachine]

But what would make the car warm straight up to 1/2 and hold there for 20 minutes Brian? A bad/wrong thermostat? The car gets up to this temp within ten minutes of driving, and hot air is blasting out of the heater.

[Brianmoooore]

If the temperature is stable, then probably the wrong thermostat. M20 = 80 degrees; M40 = 88 degrees.
Maybe 88 degrees is specified in Poland?

[daimlerman]

Could also be a build up of silt in the cylinder block water jacket,thus reducing coolant capacity.

[Brianmoooore]

If the temperature is stable

Anything like that, Malc. and the temperature wouldn't be stable.

[daimlerman]

It doesn't help that the temp gauge is a bid odd; once the needle approaches the 3/4 mark, it starts flickering around wildly and only settles down when the temps come back to 1/2.

Does not read like the temp is stable to me,Brian!

[Grrrmachine]

Malc, it's stable unless the car is sat in traffic for over 20 minutes. As long as traffic is flowing, even stop-start city traffic, then the temp is almost rock-solid at the 1/2 mark.

All Polish E30s were imported from Germany (no BMW dealerships in the 80s), so chances are someones replaced the 'stat on the cheap. I'll do the viscous test first to confirm though, but I don't remember it ever sounding very noisy.

[Brianmoooore]

It doesn't help that the temp gauge is a bid odd; once the needle approaches the 3/4 mark, it starts flickering around wildly and only settles down when the temps come back to 1/2.

Does not read like the temp is stable to me,Brian!

Missed that bit! I think Mr Grrr should consult the wiki, where he'll find something about flickering needles being down to a loose nut on the back of the gauge.

[daimlerman]

My thoughts,FWIW,is that a reduction in water jacket capacity would cause localised boiling,leading to a flickering gauge,as the gauge sensor is mounted on the top of the engine rather than the radiator.

In old car circles,in general,silting up of the water jacket is not un-heard of.Chemical cleaning at major re-build time does not shift the stuff,a welding rod down each coolant hole in the block to loosen the crud is required,along with removing the welch washers to allow the stuff to be poured out.

[capri_rob]

IIRC all my E30's have run at between 1/4 and 1/2 - cant remember any having run at over 1/2 even in blazing heat and traffic.

Try changing the viscous as you've changed everything else
Is the fan shroud in place ?
Fan blades all present and correct ?

[Brianmoooore]

The temp. sensor has too much thermal inertia to be able to produce anything I'd describe as flickering.

[Grrrmachine]

If it's not the actual nut Brian, is there a chance it could be something else, such a dodgy earth to the cluster?

[Brianmoooore]

Could just be the whole copper pad that the nut tightens down onto has torn away, but it won't be a problem with an earth connection to the whole cluster, as that would affect other things as well.
A faulty brown sensor could cause flickering, as could any poor connection all the way from the sensor to the gauge, but these would cause the needle to drop rather than rise, as seems to be the case here.

[bss325i]

Slightly off topic but you mentioned it in your initial post, you don't need a tropical rad if you have air con.

There is an air con spec rad which is deeper than standard then there is the tropical one which is wider and deeper.

[Grrrmachine]

Rad choice was purely determined by availability Barry. Unless I ask the dealer, spares in Poland aren't always easy to come by (although it's getting better now).

Alright, thanks very much guys; I have a lot to go on now. The car's due a service at the end of the month, so I'll re-try the dash nut and if that doesn't fix the flickering then a new thermostat and viscous will go on as preventative maintenance, since I don't know how old the current ones are anyway.

[zd3bx]

By the way, don't get too stressed about the needle moving between 1/4 and 1/2. Mine does that sometimes and it's nothing to worry about.

Like it's mentioned in the Wiki, the temperature difference is very minor between those marks.

P.S. Viscous coupling is left-hand thread...As if you didn't know that

[Grrrmachine]

Cheers for the tips. It's good to know the Wiki's there in case people get stuck

[BenHar]

Ben

[Brianmoooore]

Once up to temperature the needle shouldn't move at all, except in slow moving traffic or stopped traffic, when it should increase slightly.
If the needle drops back from its correct position, the thermostat isn't seating properly (probably one arm of the mount for the working bits broken - very common with BMW 'stats) and should be replaced.

[Grrrmachine]

How embarassing...

I took the clocks out and tightened up both brass nuts. Now the temp guage sits just below the half-way line and stays there, even in commuter traffic. It's still warmer than I'd expect, so I still may have the wrong thermostat, but everything seems to be working well now - no flickering or going in to the red.

[jimbom30cab]

Great news, i'm glad the Wiki was helpful also, well worth looking at for problems like this.

Nice fix

[gromgsxr]

i changed the stat on my car to a aftermarket one and found that my temp gauge sat at the halfway point, before it used to sit 1/4 mark even though the both had the same opening temp

[Brianmoooore]

i changed the stat on my car to a aftermarket one and found that my temp gauge sat at the halfway point, before it used to sit 1/4 mark even though the both had the same opening temp

1/4 = 80 degrees; 1/2 = 88 degrees. Which one is wrong? New or old 'stat?

[gromgsxr]

both were marked 80

[Brianmoooore]

I'd put the old one back!