What would make the coolant temp gauge act erratically? Sometimes it works normally, other times it doesn't move when I start the engine. Could this be messing with performance, gas milage and/or cause rough idle? Could it be the reason that my plugs are a bit fouled? I know it's only 30 bucks, but I don't want to spend the money to replace it if I don't have to. Also, as an aside, what thermostat do I need to use? I see that FCP has an 87° and 92° version.

 

Hi,

>What would make the coolant temp gauge act erratically?
Either a faulty sensor (thermistor) or low coolant level (on some cars, the sensor has to be completely immersed in coolant or they read erratically or won't read at all).

>Could this be messing with performance, gas mileage and/or cause rough idle? Could it be the reason that >my plugs are a bit fouled?

Yes it could, as the ECU is misinterpreting the coolant temp and supplying more fuel than is necessary when the engine is hot.

If you don't want to spend money on a new ECT sensor, I would test it by draining some coolant, removing the sensor and heating it in a pan with water in it, with digital multimeter attached to it. If the sensor is fine, the reading on the meter should read less Ω.

87 & 92 degrees in Celsius is not much different, but generally the 87 seems to be used on turbo.

I hope this gives you some ideas.


JPN

 

Hmmm. Yea, you've given me some things to think about...

What about when the engine is cold? Would this cause any idle problems (rougher than when warm) or maybe cause the engine to flood?

 

A faulty ECT sensor could cause rough idle regardless of the engine temp, as well as flooding the engine by spraying excessive fuel.

Rough idle is one of the most common problems as well as one of the most difficult problems to diagnose. It could be the IAC (Idle Air Control) valve, cold-start injector malfunction (if so equipped), or neglected tune-up/maintenance (this is by far the most usual cause[8D])etc...

I would try AutoZone or other parts shops that provide free OBD-II diagnosis and see what the ECU says. I am however a bit skeptical about Volvo's self-diagnostic system; sometimes it doesn't seem accurate.

Let me know if you need any more ideas. Tech should be back in a couple of weeks I believe.


JPN

 

I was thinking Idle Air at first, but started leaning to the temp sensor. I was thinking the rough idle is somewhat erratic and sometimes it runs like a dream, and figured that the IAC would be more of a constant problem.

1993. No OBD-II connector :\

 

>1993. No OBD-II connector :\
.

But you have the power of OBD-I!!!

I went through the factory manual and you do not have to remove the ECT sensor to test it. Simply check for the specified resistance values, see below (but be sure to check OBD-I first):

32F: 7300 ohms
68F: 2800 ohms
176F: 300 ohms
212F: 150 ohms

I would check 32F & 212F ohms, as you can't really tell when the temp is at 68F or 176F. Also, see if you can disconnect the ECT sensor and if the ECU stores code for it. But this may have to be done with the power off to avoid damage to the sensor.

I hope this gives you some ideas.


JPN

 

Sweet, I'll try that tomorrow... Now, just where exactly is the sensor located

Just out of curosity, would a pre-heat hose that's all kinds of shot contribute to cold idle problems? I bought a new one, but havne't had a chance to put it on and am curious...

 

The ECTsensor islocated closeto the thermostat housing. The electrical connector is close to the alternator.

I'm not sure as to the pre-heat hose, as my 850 was a turbo and did not have pre-heat hose. Wait till someone with non-turbo replies.


JPN