Water Temp Gauge

[TheSeeker]

Hello All, I am currently having an issue with my water temperature gauge. It is an aftermarket sun pro unit mounted under the dash, it is mechanical. The sender goes to the thermostat housing.

My issue is that this morning, I noticed while driving on the freeway that the temp said a little over 120 degrees. When I got off the freeway and was idling at the red light, it was was still around 120, and when I hit the throttle it went down to 100 degrees before bouncing back up.

I parked and shut off the motor and popped the hood, felt the radiator hoses and heater hoses and checked the fluid level in the overflow bucket all seemed ok, no leaks, worn parts or cold hoses.

My question is as follows, Does this sound like the gauge/sender is bad and needs replaced or is there another issue in the cooling system ( stuck open thermostat, water pump failing, etc) I should look into first. I have no idea how old the gauge and sender are, they were on the truck when I received it from my dad. I would just like to get on the right track. Ive lived in phoenix my whole life never had a vehicle run under 130 degrees lol.

Engine is 250 six, manual trans.

[leftybass209]

Well, your engine really wouldn't run and maintain a temp of 130. I'd say your gauge or sender is faulty. A quick check would be to pull the sender and drop it in boiling water.

[michael bustamante]

yup check the thermostat in boiling water and maybe bleed the coolant. it might have bubbles in it (air pockets)

[TheSeeker]

So, to clarify it seems I have two answers..

1. Remove the gauge and sender and take it inside to place probe in boiling water and read temp at gauge

2. Remove thermostat and verify if it is open all the time or operating correctly in boiling water?

[michael bustamante]

actually, to make sure the thermostat closes. it could be stuck open

[hamjet]

I had the SUNPRO gauge that stopped working all together. it started doing what yours did, then it would hardly register. the unit is all one piece and there's no way to fix the problem other than buy another one like I did. but test it first in boiling water to make sure first...

[TheSeeker]

Good Info Hamjet!, I need to go home for the day soon and will check the sender and thermostat when I do, but after driving on my lunch break and checking everything again Im pretty sure its the gauge. It stays at the 100* mark and will start to move up towards 120* and then back down to 100 again. Idling and at cruise.

[bonnieclyde100]

did the gauge just start reading this way or has it always read this way? if it just started i would lean towards the thermostat being stuck wide open. i had mine do that and the temp only went as high as 120.

[hamjet]

Yea, definately test both. you have to drain the coolant down any way so test the thermostat and the gauge senser. just drop the senser in your cup of coffee after you unscrew it out of the block..

[GRX]

You said it is a mechanical temperature gauge. Make sure the Capillary tube is not kinked or damaged in any way since that will effect the pressure sent to the gauge element. Thus giving false readings.

[TheSeeker]

Well, I verified the engine running temps with a temp gun and it is the gauge not the thermostat. everything is working correctly except the gauge, it now reads a flat 0. I need to get a new one any suggestions on brand, etc?