OT: I'm getting hot warning

[whiskychaser]

Reading Gene's post about radiator puking coolant and BigKriss's post about headgasket blowing has got me thinking. Yes I know its dangerous. We have got 4 sensors on the car and none are bright enough to tell us BEFORE the engine gets too hot and does some damage:
The engine temp sensor must tell the ECU but it keeps it to itself
The low coolant only works when the engine is stopped - bit late then
The aux fan wont cut in if the coolant is low because the sensor isnt in contact with hot coolant. So that wont save the day
The temp sensor may tell the gauge but thats not very accurate and you might not notice it till its too late anyway
So I'm thinking why not link into a temp sensor circuit that will bring on the 'low coolant' warning and the accompanying 'bong' while the engine is running? Wouldnt want to meddle with the ECU circuitry but the gauge sender is a likely candidate. The E34s suffer from overheating and the E39s even worse. Any thoughts or should I go find a good book....?

[DaveVoorhis]

It's already there! At least, it is on the E39 with the high OBC and I vaguely recall it's on the E34 with the OBC. If the temperature gets too high (for some unspecified value of "too high") it bongs and puts COOLANTTEMPERATURE on the instrument cluster display.

Unfortunately, I suspect the message only appears at a temperature hotter than that required to turn an aluminium head into a puddle of dripping molten metal. I'm not about to test it.

[philbyil]

Never trust idiot lights!
Just one of the reasons I installed oil pressure, oil temperature and voltmeter gauges!

[whiskychaser]

It's already there! At least, it is on the E39 with the high OBC and I vaguely recall it's on the E34 with the OBC. If the temperature gets too high (for some unspecified value of "too high") it bongs and puts COOLANTTEMPERATURE on the instrument cluster display.

Unfortunately, I somewhat suspect the message only appears at a temperature somewhat hotter than that required to turn an aluminium head into a puddle of dripping molten metal. I'm not about to test it.

You see a lot of E39s advertised with 'just' a blown head gasket. I read that as it got too hot and probably pulled the bolts out of the block so the engine is totally fkd. It doesnt have the high coolant temp warning on mine. But you have posed a very good question- how hot should the engine be when you get the warning?

[tim eh?]

If the temperature gets too high (for some unspecified value of "too high") it bongs and puts COOLANTTEMPERATURE on the instrument cluster display.

I got that message just about exactly when my headgasket blew I think.

[whiskychaser]

I got that message just about exactly when my headgasket blew I think.

That unfortunately proves the point. You get a light that tells you the fuel is getting low but nothing to say that your engine is about to blow up

[DaveVoorhis]

You see a lot of E39s advertised with 'just' a blown head gasket. I read that as it got too hot and probably pulled the bolts out of the block so the engine is totally fkd.

Yeah, that's what happens. I'm half tempted to get one of those and see if I can fix it with a bucket of helicoil inserts.

[tim eh?]

That unfortunately proves the point. You get a light that tells you the fuel is getting low but nothing to say that your engine is about to blow up

Actually I was already well aware of the situation as I had heard a pop (water pump it turns out) and was watching things closely. Unfortunately it heated up really fast and I was really badly stuck in traffic and couldn't even pull over so the bong (the noise I'm talkin' yo) just made me panic more. Not sure actually when it started bonging but I was already swearing pretty loud.

[whiskychaser]

Yeah, that's what happens. I'm half tempted to get one of those and see if I can fix it with a bucket of helicoil inserts.

Me too. I have a sneaky feeling the best solution would be an old M50 block under the E39 head. Dont even know if it fits After hours of research (ok, a few beers) my colleague in the stage lighting business tells me we need a thermocouple. I only know them as the safety device to turn your boiler off if the pilot light goes out. He tells me they use them in stage amps to ditch power if they get too hot. Some have a pot so you can adjust them. So we just need the critical temp at which the switch should throw. I intend to patent this device so dont tell anybody

[whiskychaser]

Actually I was already well aware of the situation as I had heard a pop (water pump it turns out) and was watching things closely. Unfortunately it heated up really fast and I was really badly stuck in traffic and couldn't even pull over so the bong (the noise I'm talkin' yo) just made me panic more. Not sure actually when it started bonging but I was already swearing pretty loud.

Some silly arse is going to ask why you didnt just turn off the engine. There was probably enough residual heat there to fry it anyway. I'd like the system to go back a few miles (before you got in traffic) and gently but firmly advise you that all is not well in the coolant department