Solution to the Swinging Temperature Gauge

[85Dave]

My temperature gauge has been swinging for many years now. I did a search here and found others having the same problem, but no solution. Well, I think I have the solution.

I suspected the problem was that when the thermostat was closed, there was no coolant flow through the engine and the engine would heat up the stagnant coolant. In the meantime, the coolant in the radiator is getting cooled way down. The coolant eventually gets too hot in the engine and the thermostat opens up, but now too much flow is going through the engine and the cold coolant overcools the engine. So the thermostat shuts, and the process starts over. The thermostat must be in an area that is cooled somewhat, as it doesn't seem to properly sense the bulk coolant temperature.

I took my thermostat out, and drilled a 1/8" hole in the face. This allows a little bit of flow through the thermostat at all times. As the engine heats up, enough coolant is flowing past the thermostat that it will start to open before the engine gets too hot.

After I did this, I took a 400 mile trip. The gauge was steady on level ground. Going uphill, it would move a little. Going down the other side of the hill, the gauge would move back. Overall it would swing less than the width of a letter. Before, it would move 3-4 letters.

 

[Green98XLT]

Interesting... mine does that too and I was just gonna throw a new T-stat in because I think my Ex has the original one still in there. I guess I'll break down and do a coolant flush and T-stat swap here soon then.

 

[JDraper]

Why didn't you just replace the t-stat instead of drilling a hole in it? Sounds to me like it was just a sticky t-stat or it was installed upside down.....

 

[85Dave]

Why didn't you just replace the t-stat instead of drilling a hole in it? Sounds to me like it was just a sticky t-stat or it was installed upside down.....

I did try a new t-stat. It didn't help. Others have also tried new t-stats with no help. I drilled a hole in the old one to try my theory that a small amount of coolant needs to flow past the t-stat for it to work properly.

 

[roccov12345]

If you look back at my recent thread I was having the same issue. I'm thinking that your idea might actually take care of the temp issue. I think people that may have this issue in the future should first replace the t-stat to make sure that it is not stuck open/closed. If that does not work, be sure that you have no air in your cooling system. If that doesn't work, ground out your engine coolant temp sendor wire to make sure the gauge is working properly, it will go all the way to hot on the dash. If it does, go to your local parts store and change out the sendor, it's about 4 bucks and it's a piece of cake. Drive it around, if that does not work say over 50 miles of driving, then you could try to drill the hole like he's talking about up top. If that doesn't work go buy a cheap autometer gauge and install that in your stock temp gauge's spot lol. Good Write up.

 

[Runnin'OnEmpty]

You might be on to something, Dave. I always drill my new thermostats as a matter of course, and it does seem to stabilize the temp swings somewhat. Lots of new thermostats have the hole already there, with a tiny relief valve installed.

My main reason for drilling the holes is to allow for air to escape out of the block when refilling with coolant.