Engine temp fluctuation.

[Hugetanker]

Over the weekend I went on a trip for the New Year. While driving I noticed that my temp guage was fluctuating pretty pretty drastically. While I understand engine temp will fluctuate, I didn't think it did it so much so quick. And the thing is, it isn't going up, it's going down. For instance, I'll be driving and it will be about halfway where it normally is and then just for a few seconds it will fall to just above the cold line. Then go up to about quarter where it will bounce around a bit then go back to normal. But it won't go up. Just down. Anybody have any input on why it's doing this?

 

[Muadeeb]

Either an air pocket in the coolant or an intermittent/corroded connection at the sensor or a sensor going bad. Can you hook it up to a scanner to monitor the ECM's sensor while driving?

Remember that the dash gauge has a different sensor than the ECM

 

[granitex]

If you have not done anything else, like had the rad out, or a coolant line out. I would put money on the temp sensor itself.

 

[drbandkgb]

I bet it's the air temp sensor.. Right on top.. The sensor breaks really easy mine did that I wiggled the wire and it's back to normal


Sent from the satellite of love..

 

[Cyclemut]

Usually, when the gauge goes down, it's one of two things. The gauge will normally go down after the t-stat has been open long enough for the cool coolant to have gone through the engine (from the radiator) and then then t-stat will close. You notice the gauge moving only when the cool version of the coolant finally makes all the way through the engine and finally makes it to the t-stat.

The second thing is as mentioned above. The tab on the sensor (the single tab'ed one is for the gauge) can become loose. I usually take a screwdriver and, very lightly as they're fragile, tap the rivet to make the tab tighter. Use a hammer on the screwdriver, but again, be gentle. If it still continues, try bleeding the system. But that will usually make the gauge go up.

 

[granitex]

If you do decide to bleed the cooling system be kind to the bleed screw. It is actually a bolt on the top on the intake manifold and if you brake it you will not be very happy with yourself.

 

[Hugetanker]

Thanks for the input guys. I do have a very very slow coolant leak from one of the hoses that will be replaced along with the timing belt in a month or so. So I'm thinking maybe there's an air pocket. If that doesn't fix it, I'll go down the line of other causes. It isn't overheating so I'm going to check things one at a time so I know what the actual cause is.

 

[AbuseTheElderly]

I had the same symptom with my truck before this happened. We went down the mountain from the windmills at Coal Creek, the road was very steep and we used our engine as a break in 1st gear. Halfway down the mountain I noticed the temp went from the normal warm temp to completely cold. We got a check engine light with P1126 as the code later that day. If you're X is not reaching running temp and you don't show an SES light with the above code then it may just be your gauges' temp sensor that is loose/corroded causing fluctuation, yet your ECU's temp sensor is seeing nothing wrong. It only took our X about 6 hours to throw a SES light after the first temperature drop, ever since then the needle has sat just a mm or two below "normal" running temp and the SES light is still on, so apparently both of my engine temp sensors are detecting the same thing.

Not trying to threadjack, just trying to add some (possibly relevant) info. Best of luck to you HugeTanker!