Cooling system questions - BMW Forum

broketiltuesday · 03-30-2004, 05:03 AM

Hi, I have an '87 318 M10 engine (carburetted). When I take it for a short run (maybe less than 30miles) the engine will warm up and stay around 75% temp, the third peg. Some way clear of the red, but closer than I'd like.

I replaced the thermostat a couple of months ago from one that failed to the OPEN position to this which is installed correctly and I'm certain the cooling system doesn't have any air locked in it anywheres. All the cabin blower-heaters work just fine.

If I keep going though, and we're talking mainly motorway (highway) driving here, 70-80mph, sooner or later, it's like something gives in the cooling system and the needle jumps back to 50% where it stays.

Is this normal behaviour? The engine is never dangerously hot, but I would expect it just to get to halfway and stay there rather than getting so hot first. I think the thermostat full-open postion is at 82 degrees -- I was told this was right for my car but now I'm wondering? The radiator-cap rubber looks in good condition, the fan clutch is in good shape and there are no coolant leaks.

Where is the coolant temp sensor located in this engine? I might try testing that. Haynes is pretty vague on this and Bentley manuals are quite rare here in the UK. Also should this engine have an auxiliary fan, I know fuses 3 and 18 are used for it, but there are no fuses in these sockets and, I might be being dumb, but I can only see the radiator fan.

Cheers.

broketiltuesday · 04-05-2004, 03:57 AM

To answer my own question, you can find the M10 temp sender and a thermovalve or something like by following the topmost hose that comes out of the thermostat along to where it enters the engine, under part of the cold air intake. Under there is a divider block, forward of the carb where various water hoses go in.

Two 19mm bolts are set into this block, one with electrical connectors and the other with vacuum hose connectors. The electrical one is presumably the thermistor, this was caked in crap, the vacuum one I'm not sure of, the ETK diagram doesn't help too much either.

The thermistor has voltage when the engine is running. This makes sense but I don't know whether it's the correct value or not so probably I will try replacing it, and when the weather gets warmer do a full coolant flush or something.