E30 Zone

Hi everyone,
I have an issue with my 1987 325is 5spd. For some reason the temp gauge now rests at the 3/4 mark. It's been like this for about three weeks now. The car doesn't overheat because I can idle for time and it wont move further, though when I turn off the car and go back 5-10m later the needle is normally just under the half mark. This indicates to me that the thermostat is functioning. The clutch fan is spinning properly with resistance, and the heat is blowing as normal. I will add that when I blow the heat at full speed, it doesn't change where the temp needle is.

Occasionally, when I am in the lower gears (2nd &3rd) I can get the needle to move slightly cooler, but it normally returns to the 3/4 mark at cruising speed.

PS. warm-up time is normal and I don't seem to be experiencing any other issues as my mileage is consistently 26-28mpg

Here is a picture of where the temp gauge sits (I took it while actually driving)......

maybe worth whipping the instrument panel out and checking the brass nut on the back of the temp gauge, also the brown sensor that works the gauge could be at fault..thats if the car isn't actually overheating and it's just a case of the temp gauge being incorrect

When was the last time the cooling system was flushed?
sounds a little like a dodgy rad, or waterpump not doing its thing.

thanks for the replies, I did bang it a bit to no avail. Perhaps, I'll resort to removing the cluster.
I did the water pump & timing belt about two years ago +-30k, and I flushed the coolant last summer.

I was thinking that maybe the radiator was clogged but all of the hoses feel to touch as they should. i.e; top hose hot, etc

I think if the radiator is not 100% it will still flow and cool to a certain extent but not at peak efficiency. The running cooler in lower gears tends to point me to increased flow which may mask the restriction in flow.

Have you carefully put your hand across the radiator to check it's all one temperature? Maybe take the grill off and check from the front to avoid that hand shredding fan.

I flushed my coolant when I got my car but I spent a couple of days doing it until I was happy it was nice and clear. When you flushed yours did you take the bolt off the side of the block under the exhaust manifold and drain the block too?

Doh! I didn't remove the block bolt when I flushed last time. It looks like I have a diagnosing to do this weekend.

All of the hoses were hot except for the lower hose going to the block, which is lukewarm

The block plug is important if you want to do a thorough flush, supposed to be tricky to get on and off but I didn't have any problems

I'm not sure which way the coolant flows but if the lower pipe is luke warm in comparison to the upper then there's certainly something amiss. Good luck with the diagnosing, if I were a betting man I would be betting on the rad. They're very easy to take out and flush/back flush, but I would check it by hand first while it's in the car and warm to make sure.

ok, I believe I may have fixed the issue. I replaced the thermostat this morning and the heat is hot, and the needle is hovering right below/at half....I'll update as need. Thanks supafly for your insight.....if I continue to have problems I'll replace the radiator. Though, I think I should have just went ahead and replaced it while I was involved with this...

Looks like I'm a bit late in on this thread, but this is a thermostat issue, or nut on the gauge.
If it were a radiator problem, the gauge reading wouldn't be consistent - it would go higher when the engine is worked hard, and come back to normal when lightly loaded.

thank you for the reply, you reply was confirmed this morning. I hope that someone in the same predicament comes across this thread.

Glad I could offer a bit of support, and good to hear it's sorted.

Thanks for the clarification Brian.