running temperature

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angoose
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Mon Apr 15, 2019 8:38 pm

Hey all,

Need to pick your brains again.

A little back story. The car was running fine and then the temp gauge started creeping up to 3/4 and stayed there. Then climbed higher so I pulled into the services. I let it cool and topped up with new coolant then set off, not far down the road I had the same problem. Got picked up by recovery guy he suspected head gasket.

Upon getting delivered back to me I started to try and work out if it could be anything else. No leaking hoses etc. So i swapped out the thermostat and so far so good. Been out on a few short drives and go a bit further each time just to see how we get on.

All seems good done a bit of town and country roads and been out for an hour or so but the car doesnt seem to get up to half way on the temp gauge. Running between 1/4 and half. Is this a problem? I havent done a motorway run yet but a little apprehensive to do that just yet.

Many thanks,

Angus
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Mon Apr 15, 2019 8:43 pm

Between 1/4 and 1/2 is the correct position for the temp' gauge
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angoose
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Mon Apr 15, 2019 8:46 pm

Cloggy Saint,

Thanks for getting back to me so quick on this. Glad to hear that. I figured it should be ok but after it over heating been watching the gauge like a hawk.

Thanks again
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BenHar
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Mon Apr 15, 2019 9:00 pm

Cloggy Saint wrote:
Mon Apr 15, 2019 8:43 pm
Between 1/4 and 1/2 is the correct position for the temp' gauge
True for a 6 cylinder engine which should have an 82 degree 'stat.

If it's a 4 cylinder it should have an 88 degree stat and run at the halfway mark.

Ben
jmc330i
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Mon Apr 15, 2019 9:09 pm

As above, all my 6 pots have run at just over 1/4, my 4 pots have all run at bang on 1/2.
James
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angoose
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Mon Apr 15, 2019 10:06 pm

Its a 6 cylinder. Thank you all for your help. I really appreciate it.
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Brianmoooore
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Tue Apr 16, 2019 9:42 am

The fact that you've asked about the correct gauge position suggests that it wasn't correct before. What's the temp. stamped on the old 'stat? Does it have BMW stamped on it?
The temp. scale of the gauge isn't linear - it's compressed at the low end and at the high end, so as long as the needle didn't go into the red, the car didn't overheat by as much as you might think.
You haven't mentioned the low coolant light in the overhead panel. If the coolant didn't get low enough to switch this on, there was sufficient coolant still in the engine all the time, so this wasn't the cause of the overheating.
M20s (with sufficient coolant in them) overheat for three reasons when they're moving - thermostat troubles, water pump rotor disintegrating or slipping, and an airlock at the back of the head in the heater circuit. The airlock, once the car has been properly bled after work on the cooling system, can only be caused by a slight leak of combustion gasses into the cooling system, either by a failed head gasket or a crack.
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angoose
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Tue Apr 16, 2019 9:55 pm

hi brianmoooore,

Thank you for taking the time to reply to question. I dont recall the coolant light coming on.

As for the temp gauge it went near red but I had pulled over then and as was getting steam from the coolant reservoir.

I asked about what position on the temp gauge as the car is still fairly new to me. When i first had the car the temp gauge ran around halfway. Then on that journey it after a while crept to 3/4.

When we changed the thermostat there was some debris in the thermostat housing. Something that looked like a but of a seal and the other vaguely resembled wax.

The thermostat appeared to have been replaced before and the seal almost appeared glued in and wasnt easy to removed but we removed it carefully and replaced the seal and new thermostat.

I queried the temp gauge position as its now running at 1/4 which it never has since i've owned it. Which is why I wanted to check this was normal.

So far ive done a good few trips and she seems to be running well.
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Brianmoooore
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Tue Apr 16, 2019 10:17 pm

If all is OK, then perhaps it was just a failed thermostat, and possibly the wrong 'stat had been fitted - wouldn't be the first time I've seen it.
BTW, if the airlock at the back of the head occurs, as well as overheating, there will be no heat from the heater, even with the knob turned fully to 'red'.
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angoose
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Wed Apr 17, 2019 7:06 am

Ok i'll check the heater when I next take the car out and let you know wht happens. thanks again
angoose
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Fri May 03, 2019 7:01 am

Hi just to let you know that the heaters working well so no airlock at the back of the head
BristolE30
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Mon Jun 24, 2019 8:05 pm

BenHar wrote:
Mon Apr 15, 2019 9:00 pm
Cloggy Saint wrote:
Mon Apr 15, 2019 8:43 pm
Between 1/4 and 1/2 is the correct position for the temp' gauge
True for a 6 cylinder engine which should have an 82 degree 'stat.

If it's a 4 cylinder it should have an 88 degree stat and run at the halfway mark.

Ben
My 316 carb has an 80c thermostat. 88 is a lot higher, was it different on certain models?

Cheers
Jo
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Brianmoooore
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Mon Jun 24, 2019 8:28 pm

BristolE30 wrote:
Mon Jun 24, 2019 8:05 pm


My 316 carb has an 80c thermostat. 88 is a lot higher, was it different on certain models?

Cheers
Jo
Criteria for deciding the thermostat opening temperature:

The hotter a petrol engine runs, the more efficient it is.
The limit is reached when local boiling occurs at some point in the cylinder head.
The higher pressure the system runs at, then the higher the temperature will be that the local boiling occurs at.


The newer an engine design is, local hot spots in the cylinder head are likely to be reduced by better design.
With newer, more advanced materials, the system pressure can be increased.

Your M10 is the oldest E30 engine, then came the M20, which runs hotter, initially at the same pressure, but increased in later versions. After that was the M40, which runs hotter again, and at the higher pressure that the later M20s run at. Finally comes the M42, which runs at the same temp. as the M40, but at a considerably higher pressure.

Your M10 engine was originally designed with a crude thermostat that simply blocked flow to the radiator while the engine was warming up, stopping the flow inside the head and causing hot spots. This was improved by adding the weird self contained 'stat assembly used on the E30 M10, which just hangs in a nest of pipes, rather than a 'stat built into the engine as on all others. The extra pipes allow the coolant flow in the engine and heater to be maintained from cold. I suspect the M20 was originally designed with a flow stopping 'stat as well, because of the excess of large coolant pipes, but this was sorted by a clever redesign of the thermostat housing, plus the extra pipes.
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BristolE30
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Wed Jun 26, 2019 11:29 am

Brianmoooore wrote:
Mon Jun 24, 2019 8:28 pm
BristolE30 wrote:
Mon Jun 24, 2019 8:05 pm


My 316 carb has an 80c thermostat. 88 is a lot higher, was it different on certain models?

Cheers
Jo
Criteria for deciding the thermostat opening temperature:

The hotter a petrol engine runs, the more efficient it is.
The limit is reached when local boiling occurs at some point in the cylinder head.
The higher pressure the system runs at, then the higher the temperature will be that the local boiling occurs at.


The newer an engine design is, local hot spots in the cylinder head are likely to be reduced by better design.
With newer, more advanced materials, the system pressure can be increased.

Your M10 is the oldest E30 engine, then came the M20, which runs hotter, initially at the same pressure, but increased in later versions. After that was the M40, which runs hotter again, and at the higher pressure that the later M20s run at. Finally comes the M42, which runs at the same temp. as the M40, but at a considerably higher pressure.

Your M10 engine was originally designed with a crude thermostat that simply blocked flow to the radiator while the engine was warming up, stopping the flow inside the head and causing hot spots. This was improved by adding the weird self contained 'stat assembly used on the E30 M10, which just hangs in a nest of pipes, rather than a 'stat built into the engine as on all others. The extra pipes allow the coolant flow in the engine and heater to be maintained from cold. I suspect the M20 was originally designed with a flow stopping 'stat as well, because of the excess of large coolant pipes, but this was sorted by a clever redesign of the thermostat housing, plus the extra pipes.
Interesting. Thanks for that Brian.

My engine temp has been creeping up just above the half way mark, pretty much since I bought it. It definitely increases at stops, then cools down a bit once going, especially going down hill. Replaced the thermostat and it seems to be working (lower rad pipe hot). Another interesting thing I noticed yesterday was that the heater matrix made a strange gurgling noise the other day and the engine temp instantly went up a bit - do you have any ideas what this could be? I did notice some coolant marks on the side of the glove box (photo), but I figured it was from an earlier accident.. Thinking of replacing fan clutch but it does seem to be working. May also try some Holts Speed flush as I guess radiator could be a bit clogged. Photo attached of where it fluctuates too...

Appreciate any help
Jo
77711B45-67DD-41A2-AD52-76983B194ABA.jpeg
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BenHar
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Wed Jun 26, 2019 4:34 pm

If it increases when stopped the fan clutch is on it's way out.

Ben
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Brianmoooore
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Wed Jun 26, 2019 6:05 pm

BenHar wrote:
Wed Jun 26, 2019 4:34 pm
If it increases when stopped the fan clutch is on it's way out.

Ben
Viscous fan coupling isn't triggered to lock until hot enough air is reaching it from the centre of the radiator. By this time the coolant temp. of the engine will have crept up a couple of degrees. If the needle climbs as far as the 3/4 white mark or continues gradually creeping upwards then the fan coupling is suspect.
It's a crude system, but because of the low component count, tends to be a reliable system.
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BristolE30
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Wed Jun 26, 2019 9:03 pm

Brianmoooore wrote:
Wed Jun 26, 2019 6:05 pm
BenHar wrote:
Wed Jun 26, 2019 4:34 pm
If it increases when stopped the fan clutch is on it's way out.

Ben
Viscous fan coupling isn't triggered to lock until hot enough air is reaching it from the centre of the radiator. By this time the coolant temp. of the engine will have crept up a couple of degrees. If the needle climbs as far as the 3/4 white mark or continues gradually creeping upwards then the fan coupling is suspect.
It's a crude system, but because of the low component count, tends to be a reliable system.
Is it normal for my temp gauge to be creeping up like this? It’s disconcerting to say the least as it feels like if I really ran it hard it could go higher. I’ve heard some people say it should never go higher than half.

What were your thoughts on the gurgling noise? And the Holts Speed Flush? I’ve heard people getting good results from it...

Cheers!
BMW E30 316 - M10 with Weber Carb :bmw:
Bristol, UK
BristolE30
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Wed Jun 26, 2019 9:04 pm

BenHar wrote:
Wed Jun 26, 2019 4:34 pm
If it increases when stopped the fan clutch is on it's way out.

Ben
Thanks, yes I think may just replace it as it’s probably never been. Could help!
BMW E30 316 - M10 with Weber Carb :bmw:
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