Cooling issue... just need confirmation....

[maxmonster]

Hey guys... so today my car started to overheat while driving home.

Thermostat, water pump, and clutch fan have all been changed out less than 5k ago.

As I look into the overflow I don't really see the coolant level change... coolant is flowing freely from the bleed screw without any "burps."

Radiator? Anything else I'm missing? :(

[cgk_iii]

Im Going through the same thing you're going through right now. Expansin tank, thermostat, water pump, and fan clutch all replaced. Only thing left to replace is the radiator but I don't want to drop $200+ on a new radiator if it's not going to fix the problem. Let me know if you find a solution.

[kwill22]

when you replaced it all did you run the heater while bleeding it? thermostat turned the right way? when you feel the hoses is the passenger side hose a lot cooler than the upper driver side hose?

just a few things to check to narrow it down

[maxmonster]

Thermostat is installed correctly. Heater full blast while bleeding. Upper hose does seem to get warmer than lower however... Both are warm

[CorvallisBMW]

All that sounds correct... hmmmm...

Did you try bleeding with the front end of the car raised? It might also be worth the time to pull out the thermostat and test that it's working correctly. It's entirely possible to get defective thermostats new out of the box.

[maxmonster]

All that sounds correct... hmmmm...

Did you try bleeding with the front end of the car raised? It might also be worth the time to pull out the thermostat and test that it's working correctly. It's entirely possible to get defective thermostats new out of the box.

That's what one of my buddies said... How would I know if it's a properly functioning thermostat?

[bmwman91]

When you bled it, how much air would you say came out? Or, as you bled it, how much coolant did you have to add to the expansion tank as the air left and the level dropped?

Bleeding the M42 is SUPER simple, on ONE condition. There is a bypass groove in the thermostat housing that allows 90% of the air to come out within 10 seconds of starting the engine, and it happens that that bypass groove gets plugged up with gunk and deposits on just about every high mileage engine. In that case, it is a pain to bleed things because you have to wait for the thermostat to open, and it is lower down than the groove. So anyway, you may just have a big air bubble trapped in there and you'll need to bleed things well to get rid of it...which is scary because the engine needs to warm up, and if it is an air bubble your temp gauge will look unhappy.

Here's the groove I refer to, for reference.

[maxmonster]

Well when I replaced my thermostat I cleaned the crap out of the housing... I'm just going to replace it again... Eff it not that costly and I can do it in under an hour now... So there should be no sort of gasket sealer in that groove? I may have clogged it with some dirko... Also I noticed today that the temp needle likes to bounce while driving every little bump and what not the needle will start bouncing... Is that the grounding but behind it?

[bmwman91]

Oh. Well before you throw money at anything you need to check 2 things. First is the connector for the temperature sender (the single-wire one) since it frequently breaks at the connector. If that checks out, then you should check the gauge's ground nut on the cluster.

[CorvallisBMW]

That's what one of my buddies said... How would I know if it's a properly functioning thermostat?

Put it in a pot of hot water on the stove, preferably with a thermometer so you can monitor the temperature. Heat the water to the specified temp on the thermostat and check that it opens. if it doesn't, try increasing the water temp. If it hasn't opened by 10-20F above the stated value, it's bad and needs to be replaced.

[maxmonster]

Thnx for help guys. I went ahead and ordered a thermostat in case it ends up being a faulty thermostat. Hopefully this fixes it... been having cooling issues since I bought this sucker... *le sigh*

Also since I will be installing/reinstalling the thermostat is the thermostat supposed to be straight up and down relative to the ground or straight up and down relative to the top of the slant of the engine?

[bmwman91]

I don't think that the orientation matters really. As long as it is facing the proper way you are good.

Check those electrical points too.

[staples]

I finally succumbed to making an account so I can post.

There should be an arrow on the thermostat that is supposed to point up iirc.
Which I thought was supposed to help air get through that little opening/valve for bleeding... but not entirely sure on that one. I definitely remember there being an arrow
Now that I see what bmwman pointed out I'm not sure what it's for anymore

My car is having the same problem as well. The gauge is bouncing around and it is overheating a couple ticks past half. Bled so many times facing uphill until giving up.

PO said tstat was recently replaced so I didn't bother. The rubber gasket for it was stuck in the groove of the housing leaving an impression, which is probably blocking off the air/coolant flow now....

Maybe time to try a new tstat/rubber gasket also.
And test the sensors

Everything else has been cancelled out. Well not positive on the water pump but top radiator hose read 140F and bottom was about 95F which I think is normal

[maxmonster]

^last time this happened to me the tstat and water pump was bad and I had a coolant leak from pump!

Well ok guess I'll install tstat with arrow pointing up then...

[staples]

I'm leaning on just an air bubble since the gauge bounces around sometimes like you mentioned earlier also. The bouncing was worse until I repeatedly bled it a few days in a row. I'll probably have to reinstall a new tstat to do it correctly and you can figure out if you have the arrow pointed up. Hopefully that solves both our problems

AFAIK there is no coolant leak after replacing the radiator. Just an oil leak because I didn't install the timing case back on quite tight enough. It can be a real pita from what I've read