How tell if coolant temp is lying?

[e30onBBSs]

Alright so I did the 2.7i head swap drained all the coolant new water pump new tb etc. I'm pretty confident in my bleeding abilities.

The odd thing about it is that when the car is parked at idle or at a medium RPM that the temp gauge stays in the middle. Only when I start driving it it begins to climb, and never touches the red but is extremely close. This is weird because there is no airflow through the engine when it's parked, but all of a sudden at the same rpm while driving it starts climbing. Then I park it and it drops back to the middle which doesn't seem like it would happen if it was really overheating.

How can I test to see if the car is really getting hot/ about to overheat or if it's just a sensor or some wiring?

[LJ851]

Get an infrared heat gun and measure the temp of various cooling system parts.

[e30onBBSs]

Get an infrared heat gun and measure the temp of various cooling system parts.

I was thinking about that. What temperatures would I like to see? I know the thermostat works because the lower rad hose doesn't get hot until op temp, while the top one gets warm/ hot pretty quick

[LJ851]

Well, if you aim the gun at the temp sender you can verify the actual temp when the needle is near red and see if it matches. I use it to look for big temp drops or changes in the system, 100 degrees drop from top to bottom rad hose would indicate low flow through the rad (faulty thermostat) . Basically, the head outlet should be the hottest and the outlet at the bottom of the rad should be the coolest.

[mr.vang]

That happen to my previous e36 318i. I got the two temp sensor plugs (dme temp and gauge temp) switch after I fixed my leaking intake manifold. I switched the two plugs and solved the problem. I'm not sure if e30 has a dme temp sensor though.

[e30onBBSs]

How tell if coolant temp is lying?

so I thought it could be the belt slipping because it was a little loose, so I swapped it in like less than 5 minutes to a smaller one.

I look down, there is a little puddle of coolant on the ground, wtf? The radiator drain plug was leaking. 30 minutes of weird strategies later, the aluminum caulk I used on the BBS's sealed it. I waited about 25 minutes for it to dry. Sweet, let's take it for a drive and see if it stays cool!

Cranks and cranks, finally starts (I think fuel pump o-rings not holding pressure or something) "I'm so happy it started".

Before I even get out of my spot, this terrible sound is coming from the front, I check it out. 3/4 of the water pump pulley bolts dethreaded themselves. Luckily I was not in motion, so I got all the bolts off the ground and threaded them in. Then I tightened them all hard while holding the pulley in place with toother oil filter wrench. Then I pulled out, another anxious wait in the now head swapped, nice sounding e30 that has given me so many headaches..

And it stays cool for longer than normal, about 3 km, the gauge went a bit past 2/3.I get back to home base and there is some steam coming out of the hood but not a lot and the temp was steady at the last white line (3/4?). Pop the hood expecting some spilled coolant or whatever on the manifolds- but nope. This happened because my dumbass didn't tighten the clamp a few days ago when I was pouring coolant into the upper rad hose in a random parking lot after this happened to the mini I drive, and I tried getting the e30 up to snuff in a rush. MINI E30

Safe to say my e30 is my nemesis right now lol.

I might pick up a heat gun still, but maybe, just maybe it only started to climb because it pissed all it's coolant. Gotta bleed it again and see...

Thanks for the responses!

Tl;dr mini took a shit, tried prepping e30 in a rush, didn't tighten a hose clamp, and it bit me in the ass today

[Das Delfin]

^ that's ok, when I test drove my new front wheel bearings I forgot to tighten the lug nuts

[e30onBBSs]

Aite the radiator was rubbing against the fan a tiny bit- one of the screws came out. I bled it again and it runs mint!

I guess it was the combo of loose belt+ fan not spinning as fast as it should be anways.

[LJ851]

Are you on drugs?

[Chroma Aberration]

Are you on drugs?

Are you *not*?

[agent]

Are you *not*?

One hundred internet points to you for that reference.

[dude8383]

Aite the radiator was rubbing against the fan a tiny bit- one of the screws came out. I bled it again and it runs mint!

I guess it was the combo of loose belt+ fan not spinning as fast as it should be anways.

i'd have a look at those engine mounts if i were you. you may end up destroying your radiator some time in the near future at this rate...