M20B27 mild overheat

[Blau]

I have an '86 325e that is slightly overheating at idle.

When idling for a period of time (~3-5 mins), the needle will start moving past the 1/2 mark. It'll slowly creep up to the 3/4s mark, but I haven't braved past that.



During normal driving conditions the temp will drop down past the 1/2 mark:




I've been following this checklist:

http://www.e30zone.net/e30zonewiki/index.php/Cooling


The things I've done/replaced recently:

• Wahler 80c thermostat
• Fan clutch (I'm on my second Beyr unit in the past 6 months) Checked with newspaper today.
• Aux fan resistor
• Bleed system on jack stands
• Water pump and head gasket was replaced by a BMW dealership in 2015.
• No debris in-front of the condenser or between the rad.
• Flushed cooling system. Removed rad and hoses, checked for cracks and sludge and found nothing; rad appears to flow well.

Ran distilled water in the system for a day and replaced with 50/50. Water came back clear.

Heat in the cabin blows hot constantly when engine is warm. Noticed today that the expansion tank cap just recently developed a tear in the seal and a replacement will be ordered.

I did also notice today when it starts overheating, and I open the bleed valve on the thermostat housing, the temp dips slightly. Lower rad hose to thermostat is warm at operating temp and upper is hot, but I'm not feeling a lot of pressure in the system. Am hoping this is due to the expansion cap at the moment.

Am concerned since ambient temp was 45°F and wet today and after being in storage for the past few months was looking forward to summer cruising.

I plan to order a few parts this week. Any advice on where I should continue hunting would be appreciated.

Thanks!

[estoguy]

Hey there... I have an 86 Eta as well. Mine will do the exact same thing if I'm in stop and go traffic, but it's never gone past 3/4. And that is still well within normal operating temperature. The danger zone is the red area of the temp gauge.

If it's going back down once you're back on the move, you're good. (This happens with my car)

You've done everything right in terms of checking your cooling system.

If you're worried when you're driving, crank the heat up, open the windows and turn the blower on. Yes, it'll suck in the summer, but you do give the excess heat somewhere to go and increase the volume of the coolant. It's an old trick that works.

I think you're looking for something that isn't there. When it does creep up, keep an eye on it, but don't freak. :)

[MrBurgundy]

normal,

if you're really worried about it, go with an electric fan.

[e30davie]

"It'll slowly creep up to the 3/4s mark, but I haven't braved past that."

I don't believe this is "normal" at all. the only time ive seen 3/4 on my M20 is when i had a coolant leak and half the coolant drained out.

A working coolant system including, fan, thermostat and good radiator should regulate the temperature should be pretty much stable.

I have an aftermarket VDO temp gauge and regardless of what i am doing, hooning, sitting in hot traffic, crusing, the temperature is rock solid at about 85deg. OEM fan and thermostat on my m20, and I'm in uber hot Australia.

Although you have replaced pretty much everything so much i'm not sure where to go to next....

[cscracker]

This is not normal. The cooling system should be rock solid just above the first white mark in all but the most extreme heat (100F+).

Is your fan shroud missing? How about the condition of the fins on the radiator? Checked the belt tension on the water pump? Maybe you have an unusual clog somewhere, or premature water pump failure. Is your coolant level staying up?

For reference, my car (325iX) is cooling more effectively at idle stops than yours without the clutch fan installed at all. I'm running factory Aux fan only on a CXRacing aluminum radiator. I intend to install an electric main fan at some point but haven't gotten around to it.

[digger]

cruising in free air you should be pretty close to the t-stat temp steady state, when idling in traffic on a hot day for extended periods especially if A/C is used it will creep up until the fan(s) kick in enough to keep things in check. it shouldn't go much above 1/2 under such conditions if at all IMO. some say upto 3/4 is ok but gauges read different on some depending how good the grounds are on the cluster that can shift the needle a bit i have found, and more commonly mentioned also make the needle erratic.

[ceaston85]

Blau did you ever find the cure for this issue? having the exact same problem after doing the timing belt job (pump, thermostat, seals, belt and tensioner replaced).

[ADEN]

The guy says when the bleed screw open temp decreases it he may still have air in the system.
I used to have this problem but put 60c temp switch (radiator switch) to turn the aux fan early to avoid getting this issue at idle.

[ceaston85]

I had an 80C thermostat and I put the same replacement back in. I’m guessing I have some air in the system I have to take care of. Could it also be the ignition timing is not adjusted so it’s firing too early? Sent from my iPhone using Tapatalk

[ADEN]

No timing issues just air in the system.one method help me with this issue is start engine wait till temp reach 1/2 then rev it to 3k and hold it there, open the bleed screw and bleed it for like 30 seconds then tighten the screw, drive the car for 10 mins stop and let it idle and see it there is improvement each time you bleed it you will notice more coolant than air is getting bled out, repeat 2 or 3 times till you see results.

good luck

[Gregs///M]

If the ground is bad on your temp gauge, the gauge will read hot. The worse the grounding, the more hot it will read. If your cluster is not refurbished, it will read overly hot. If your cluster is not refurbished, disregard the gauge and use an IR gun until you can have the cluster refurbished. You can also try tightening the 7mm nut behind the gauge but that will only help so much. You can also take it apart and clean all the copper oxidation, that may help a little bit too.

[ceaston85]

It started happening after I did the timing belt job so I would think the temp gauge in the cluster is fine. I’m sure I left some air by the thermostat housing I’ll try to sort it out tonight. Sent from my iPhone using Tapatalk

[ceaston85]

So for the ones running into a similar issue, I pulled my thermostat out and the new one was different. The diameter on the plunger slightly smaller. Put the old one back and the car is back to normal. I ordered a new OG thermostat. The lesson is that not all parts are interchangeable. Sent from my iPhone using Tapatalk