SETA suddenly running much warmer

[supra89t]

I have an '88 seta that I have owned for about a month. Until last night, the temp gauge normally sat just above the half-way mark, essentially touching it. Last night while driving home the temp rose to the 3/4 mark. It is no warmer outside right now than it has been for the last few weeks. This morning, the car warmed up to same hot temp as last night. When I got to work, I let it idle for 11 minutes while watching the gauge. Here are the pics:

Arrival at work (pulled in from several minutes on surface street)


After 7 minutes of idling:


After 11 minutes of idling:


While on the highway this morning at a steady 65mph cruise, the temp gauge fluctuated b/w the 1st and 2nd pics above. To me, this rules out a fan malfunction. I am leaning towards a failed t-stat, especially since this started suddenly last night. I check my gauges every few minutes while I am in the car, so it is not possible that this has been happening without my knowledge. The only weird thing I noticed was that the temp needle twitched a little for 2-3 seconds after about a minute of idling. I am hoping someone has suggestions or has had a similar problem. I have to fix the car this afternoon when I get off work and I don't feel like throwing parts at it. I just don't have the $ right now to mis-diagnose it.

Thanks for your help!

[jlevie]

Start with a new thermostat and cooling system flush.

[AndrewBird]

^^^Exactly what I was going to say. Thermostats are supposed to fail open, but they can fail closed and not allow coolant to flow.

You might also get a separate gauge to double check the temp. Could just be the gauge is malfunctioning. Pick up a cheap one from autozone or somewhere.

[supra89t]

Thanks, guys. I am going to do a t-stat and flush tonight and see how it goes. If she's still running hot, I'll get another gauge to double-check the temp.

[supra89t]

The tstat and flush helped but didn't fix it. I noticed while working that the left side of the radiator had coolant on it. I cleaned it off as I buttoned things up and today after driving 30 miles or so, the side is soaked again and appears to be coming from the seam where the plastic tank is bonded to the aluminum at the very top. Eesh. So, I guess the next step is to put a rad in it...I might as well do the tbelt/wp and cams seals at the same time. I guess the i swap will have to wait. Maybe I'll put the cam and valvesprings in while I have it all apart.

One question...would a cracked radiator cause it to run warm even if it is full of coolant? Or is it more likely that air is getting in the system and finding its way to the sensor?

[blueapplesoda]

air. when the needle twitches, it means superheated air pockets are passing the coolant temp sensor. most of the time.

mine is doing the same thing. sudden rise in normal operating temperatures, oddly coincidental it always happens around the weather change. I probably have a bad fan clutch too.

[StereoInstaller1]

The tstat and flush helped but didn't fix it. I noticed while working that the left side of the radiator had coolant on it. I cleaned it off as I buttoned things up and today after driving 30 miles or so, the side is soaked again and appears to be coming from the seam where the plastic tank is bonded to the aluminum at the very top. Eesh. So, I guess the next step is to put a rad in it...I might as well do the tbelt/wp and cams seals at the same time. I guess the i swap will have to wait. Maybe I'll put the cam and valvesprings in while I have it all apart.

One question...would a cracked radiator cause it to run warm even if it is full of coolant? Or is it more likely that air is getting in the system and finding its way to the sensor?

Yes.

Pressure leaks allow the coolant to get air bubbles in the system when the car is cooling, as air is easier to suck into the system than coolant.

Also, the effects of coolant as a heat exchanger is increased under pressure, as the boiling point is increased...think of the contact point of coolant hitting say, the cylinder walls and then basically "micro boiling" instead of simply "washing away" the heat...you get 2 things:

First is the reduction of cooling system effectiveness from vapor being in the system. Reduction of pressurization, loss of density of cooling agent, etc

Second, you have the air pocket causing an inaccurate reading of the sensor itself.

What you are dealing with is a vicious cycle: Pressure test and repair your system first.

GL!
Luke

[supra89t]

Yes.

Pressure leaks allow the coolant to get air bubbles in the system when the car is cooling, as air is easier to suck into the system than coolant.

Also, the effects of coolant as a heat exchanger is increased under pressure, as the boiling point is increased...think of the contact point of coolant hitting say, the cylinder walls and then basically "micro boiling" instead of simply "washing away" the heat...you get 2 things:

First is the reduction of cooling system effectiveness from vapor being in the system. Reduction of pressurization, loss of density of cooling agent, etc

Second, you have the air pocket causing an inaccurate reading of the sensor itself.

What you are dealing with is a vicious cycle: Pressure test and repair your system first.

GL!
Luke

That is basically exactly what I was thinking. Thanks. I did get it bled finally. I know it won't last, but for the moment the temps are back down to the middle mark. I have to put a radiator in it in the next week or so. Now I just have to check the coolant level before I leave to/from work every day until I change the rad.

[supra89t]

**UPDATE**

Put in a new radiator, water pump, timing belt, dist cap, rotor, cam seal and o-ring. The thermostat was not touched during the installation of those parts. Now she runs hot as ever. I have bled it like crazy. No air comes out when I crack open the screw, only coolant. I've bled it nose-high, on level ground, blown into the hoses, bled from the little hose on the top of the rad, res. cap on, res. cap off, blah blah blah...heater always on full blast, hot air coming from vents.

Next options are:
Slap the dash
Shoot it with the infrared temp gun
Check resistance on temp sending unit
Check grounds (i know the hood ground is almost gone but I can't imagine that affecting the temp gauge only)
Replace sending unit
Swap in temp gauge from spare i cluster I have sitting here that nobody seems to want

If none of that works...15lbs of C4 should do the trick.

[supra89t]

LOL. Shot the temp sensor bung with the infrared gun and it read 195 so I got pissed and slapped the dash. FIXED. I guess I should cancel my order for the C4. :)