E30 318is M42 Overheating Issue

[Cal]

I've recently completed a top end rebuild on my M42. First test drive and the water temperature sawed within 5 minutes. Shut it down and discovered the radiator to me cold. So once cold I squeezed the hoses with the cap off and the radiator isn't blocked. Then turned the heater on and the heater hoses aren't getting hot either? Sound like the water pump? I should note I have removed the thermostat for now.

[Gerta]

How well did you bleed the coolant? Is this a new waterpump since you did your top end?

[Cal]

I did not replace the water pump.

I didn't bleed the system at all.

[bmwman91]

Do you mean that you are running with no thermostat at all?

You DEFINITELY need to bleed the M42. It is pretty easy and takes less than 10 minutes. A lot of people seem to say that it is hard to do, but it isn't. There is a bypass groove in the thermostat housing that a lot of people gunk up with gasket sealer, and that makes bleeding a little harder. If the groove is clear when you run it, 90% of the air will come out of the system within the first 5 seconds of starting the engine (with the bleed screw open of course). If the groove is clogged, then you have to run the thing until the thermostat opens up and if there is a big air bubble (and there will be) then you will see the temp gauge max out pretty fast. You do risk damage because of that air bubble creating a hot spot though. In short, properly put the thermostat housing on with a clear bypass groove.

If you are running without a thermostat, which is not exactly a recipe for good performance and mileage, then bleeding will at least be a snap lol.

[Gerta]

^This guy knows what he is talking about. Cal, you would do well to listen to his advice.

[Gerta]

Here are a couple of links you will find handy to have bookmarked:

1. http://www.esatclear.ie/~bpurcell/318ismaintenance.html

2. www.m42club.com

If you haven't changed the waterpump, you may want to do that at the same time as the thermostat ... It is highly recommended that you get a good quality metal impeller type of pump such as Graf.

[Cal]

Do you mean that you are running with no thermostat at all?

That is correct. You have to remember here in Australia it's pretty damn hot most of the time. The only downside is water takes a little longer to warm up.

I did not notice this groove in the thermostat housing you mention. I also don't know where the bleed valve is. I will find and report back.

Thanks a lot for your help guys.

[TobyB]

I forget exactly how the M42 thermostat works, but BMW uses a bypass- style in almost
everything they make- as in, without the thermostat, there's a full- bore leak around
the radiator so you won't get water flow. You have to leave it in, or the car CAN'T cool...

t

[roguetoaster]

That is correct. You have to remember here in Australia it's pretty damn hot most of the time. The only downside is water takes a little longer to warm up.

I did not notice this groove in the thermostat housing you mention. I also don't know where the bleed valve is. I will find and report back.

Thanks a lot for your help guys.

Yes, it may be summer there, but if you really feel you are getting overheating you can change your mix to water/water wetter, get a lower temp opening t-stat, replace/clean the radiator, or drill holes in the thermostat as a last resort.

The bleed valve is a screw on top of the radiator expansion tank BTW.

[bmwman91]

The bypass groove in the thermostat housing, on the inside between the two cavities. In some cases, it is totally filled with corrosion and crap. Next time you have the thermostat cover off look for it and clean it out. And run a thermostat. The stock cooling system should properly handle outside temps up to 45C if it is working properly. Above that, you can look into an 80C thermostat (stock is 88C).

[Cal]

I've just organised an 80C thermostat. I'll fit that, bleed the system and see if it still overheats. It does strike me as odd that the heater hoses were not getting hot though.

[dsm2002]

Cal, bleeding is very necessary. In the past, not realising bleeding was necessary, I experienced the same hoses not getting hot

[Cal]

The people you see around! Will bleed ASAP.