I need some advice, recently I changed my thermostat. My old one was stuck wide open and the engine was running at extremely low temps. After putting the new 195 degree stat in i started the engine and allowed it to come up to operating temp. The gauge moved up to the 200 degree mark, then shot back down rapidly to the 1/4 mark. It then came back up, and this process repeated.

I decided to try and correct this soI replaced the thermostat again and this time also replaced the tempurature sending unit. Started it up, and again. Same problem. After driving around for a few days this time, the changes on the gauge are not just rapid, but they are erratic. It never reads that the engine is over 200, but the gauge will twitch, and bounce back and forth between the quarter mark and 200. I checked the electrical connector on the temp sending unit, and checked the wire (what I could see of them) and found no defects.

Any ideas??

Thanks.

PS: Its a 95 4.3L CPI 4x4 Automatic

 

How does your heat run? Do you get cool spots in the heat when the temp gauge starts freaking out? Could be something small like an air bubble in the system?

 

Check for air pockets in your cooling system. Sometimes these can give inaccurate readings to the temp sensor.

 

water pump?

 

the water pump and radiator are both relatively new. how would i be able to burp air bubble out of the system?

 

You need to run the vehicle up to operating temp with the radiator cap off and the front of the truck sightly elevated; passenger side slightly higher than the driver side.

Then let it cool down and repeat. All with the cap off and topping off as necessary with 50/50 mixed coolant.

 

Well, I did exactly what you said. I parked the vehicle at an angle so the pax side was slightly higher than the driver side, ran the vehicle with the radiator cap off until it reached operating temp, adding fluid as needed. Did this twice, and the second time I ran the vehicle for about 15 minutes after it had reached operating temp. I still have the problem! Except now the gauge doesn't twitch as much anymore, but it does still show wide, quick tempurature changes.

I can't really tell if there is a difference in the intensity of the heat when these changes happen. I'm not too worried about it since the gauge has never moved above the 200 mark, but I still want to fix this problem before the weather starts getting hot.

 

I was going to go out on a limb and see if anyone might have a solution to my problem.. i've spent hours going through temp cycles, pax side elevated, with the radiator cap off to burp air out of the system with no success. I just recently replaced the ECT... no success... running out of ideas. Temp guage still will move to the middle where it should be, then after just a minute will swing back down to the 1/4th mark... its almost like when the t-stat opens the engine gets a rush of cold water from the radiator..closing the t-stat and beginning the process again... any ideas at all?

 

Does the level in the overflow bottle change from cold to hot?

 

There's always the possibility that the gauge itself may be FUBAR.