Overheating: What Have I Missed?

[IAmGary]

Here's the point for story, there must be something causing my e30 m20 to overheat but I don't know what.

– replaced water pump, belts, hoses, coolant reservoir cap and radiator in May
– car was running cold in July and getting poor mileage, replaced thermostat with a cheap one I had (may have been an 88C thermostat)
– car started overheating so again I replaced thermostat this time with with a Wahler 80C, flushed rad and put in fresh coolant
– ran fine for a couple days then more overheating. replaced fan clutch, relay K1 and tested aux fan by jumpering switch
– runs fine for a few more days then today suddenly overheats on a short drive and scares the crap out of me with visions of a blown head gasket, temp gauge got over 3/4! – turned the car off immediately.
– top rad hose is hot, bottom is cold
– coolant level is high, must be due to expansion I figure

Left the car on the street for a few hours and went back to get it after it cooled down.

- top rad hose is still warm, bottom rad hose is cold
– squeeze the hoses, before and after thermostat housing and level in reservoir goes up and down
– top up my oil (didn't see any water in it but i'm not sure what i'm looking for in the dark)
– drive it home

Get home, let it idle. Temperature goes a little over halfway but not to 3/4. Tapping the gauge sometimes made the temperature go back down. Fan is spinning great, chews up a cardboard tube nicely. Turn the car off.

- squeeze all the hoses and they are super firm, system has pressure I guess
– take the lid off the coolant reservoir and coolant spills out everywhere. That seems like it means something.
– coolant level appears to be a little over the cold level mark but under the cap it's much higher, must be cause by a trapped air bubble

So what is my next step? I assume that if the thermostat was stuck closed that I would not be able to squeeze the hoses and see the level change (though maybe I don't understand how the system is constructed). Everything that normally wears out, gets gunked up has been replaced.

Am I looking at an ignition or valve timing problem?

[paperplane94]

I would start performing HG leak checks.

[IAmGary]

I was afraid of that.

[Cabriolet]

im having the exact same issue. new hoses, radiator, refreshed head, gaskets, new thermostat, new water pump. this only thing i can point to is my valves are too loose and causing the system to get a bit too hot.

my lower radiator hose is cooler also.

[Maloney]

I would start performing HG leak checks.

wouldnt the car smoke out the tail pipe if it where a leaky head gasket?

my car gets hot when stopped in traffic... but its always cooler than half way on the gauge when drive.
dont smoke at all out the tail and runs strong!

[Maloney]

but i also... have done nothing maintenance wise with the cooling system as of yet lol

[IAmGary]

im having the exact same issue. new hoses, radiator, refreshed head, gaskets, new thermostat, new water pump. this only thing i can point to is my valves are too loose and causing the system to get a bit too hot.

my lower radiator hose is cooler also.

We should meet up and drown our sorrows in some beer. Did you check the fan clutch?

wouldnt the car smoke out the tail pipe if it where a leaky head gasket?

my car gets hot when stopped in traffic... but its always cooler than half way on the gauge when drive.
dont smoke at all out the tail and runs strong!

Your problem could be the fan clutch. I get a puff of smoke when I first start the car from cold but not after that. I have heard that there are many symptoms of HG leaks, you can have one or all of them.

[Cabriolet]

We should meet up and drown our sorrows in some beer. Did you check the fan clutch?

5k on it.

[Quinthirty]

There are two fuses that trigger the fan, depending on the temperature. One at 100F and another at 210F. Check those. I think page 55 of the owners manual shows where they are, if I remember right.

[IAmGary]

For the auxiliary (electric) fan there's the two relays K1 and K6 and then fuses 3, 18, 19 and 20 but the mechanical fan should be sufficient unless it's not working or it's really, really hot.

My aux fan didn't come on that I noticed but the jumper tests say the fan works. It's possible the thermo switch isn't triggering the fan because it's broken, or the thermo switch didn't get hot enough because of a circulation problem.

My thermo switch was replaced at the same time as the rad, but that doesn't mean it's not the problem. I need to research and find out how to test it.

[WhyNot]

if you take one of the old thermostats and gut the middle and leave only the outside ring, this will eliminate it. you really cant remove it totally bc the fluid flows to quickly and doesnt pick up the heat from the motor and it does stay long enough to lose it at the radiator.
then bleed the system.
then start it up and run it for just a little while.
shut it off and feel the radiator. it should be about the same temp on the entire unit. if it has cold spots then it is clogged.
if you put a pressure tester on and start the car, then pump it up with the it running. if the guage climbs, not creeps up alittle, that pressure could be from a blown headgasket.
i would do this first in order to establish a baseline.

[TurboJake]

My thermo switch was replaced at the same time as the rad, but that doesn't mean it's not the problem. I need to research and find out how to test it.

Testing the thermo switch is easy. Very similar to a thermostat test, only with a DMM.

All you need to do is set a pot o water on the stove. Put it in.
One prong is ground (In reality it's 12v supply. But will leave it at ground for ease). The other two switch to ground when temp is met. Having a DMM with an audible continuity tone will let you know if it's working or not a lot easier than watching it to see when the resistance clicks down to near zero.

You COULD test this on the vehicle. But it's going to get toasty hot just idling. You'll need a helper watching that gauge intently.

[sayed ali]

Why 80C t-stat? Try 71C

[e30trooper]

rubber seal goes on the outside of the thermostat. Your thermostat isnt opening.

[UserError]

From what you said about tapping the gauge cluster to get the temperature to go down, the grounding nut on the back of your temp gauge could be loose. Before you keep throwing money at your car, make sure that's tight and the gauge is reading correctly.