Temp wont stay steady

[71/454]

I've put a pile of time in to figure this out and am hoping someone has had the same problem that can help. When the truck warms up the temp goes from 100 when the t stat opens down to 65, back up to 90 and bounces between 70 and 90 the whole time, oh its a 94 k1500 5.7 4l60e. When I first noticed it i changed the t stat. It ran a bit cooler and still bounced. I tried again and burped all the air, and it stopped, but ran cooler that it should. I got a bad t stat the first time and it would open at 140 instead of the 195 it was supposed to. I put in a GM one, it gets hot like the original did but the gauge bounces again. I should mention it does have a new rad cap. Anybody else have this trouble before?

[get me on the road]

If the guage on the dash is your only problem, I think you need to replace the coolant temp sender, which on my 89 silverado is in the side of the block. I think that is the one that goes to the dash, and the one that is by the t-stat feeds the computer. I think.

[71/454]

My gut tells me there is something else wrong though, because the gauge was fine when the truck ran cooler with the other t stat. It's like it starts to heat up and starts to build pressure and then the pressure bleeds off. Or it is cooling so much that the t stat starts to close, heat shoots up again it pops open again then it cools off and starts to close again. The latter is my new theory because I think my clutch fan is working too much. It doesn't stay stuck, but it seems like as soon as I touch the throttle it comes on. And also the gauge moves less on the highway, which makes sense because of the air is forced thru the rad anyway and the fan running is only helping slightly. Long and short of it is, I'm gonna put an electric fan on it anyway. It will heat up faster on the cold mornings, and hopefully sort this mess out. Besides, it is pretty cold here right now and in my experience things sometimes just don't act as they normally would in the warm, so logical troubleshooting is out.

[get me on the road]

In my humble opinion, if the guage worked fine when it was running cooler with the one t-stat, it could still be the sender in the block. Because the guage reads what it should at say 130 degrees F or below, but at 131 F or above the guage starts to bounce because the sender is bad. Just a thought.

[Old Dave]

Stant is the only brand of thermostat I will use. I put one in my 97 Suburban when I did the intake manifold gaskets just because it was the original one. I put in a Murray brand (red & white box) that I bought at O"reiley's and the damn thing opened at 175 degrees rather than 195. The mananger at O"reiley's said they have a lot of them returned that were no good.

[get me on the road]

Originally Posted by Old Dave

Stant is the only brand of thermostat I will use. I put one in my 97 Suburban when I did the intake manifold gaskets just because it was the original one. I put in a Murray brand (red & white box) that I bought at O"reiley's and the damn thing opened at 175 degrees rather than 195. The mananger at O"reiley's said they have a lot of them returned that were no good.

I am not trying to bad mouth stant, because thats the brand I like, but today I put a new stant 195 in and it is opening at about 140. So I'm guessing 71/454's t-stat that was bad was also a stant. My box said 195 and the t-stat had 195 stamped on it......????????

[71/454]

mine was a motorad. It said 195 on it too. The first one I took out was a GM one and I now know there was little or nothing wrong with it. Maybe I wiill change the sender. Would you use a parts store one, or only a delco?

[get me on the road]

If gp sorsen (I think thats how it spells/sounds) makes one I would try that first. I have had no problems with them....yet.

[72BLUZ]

everything has been named for trouble shooting. if you have a new rad cap, and a new thermostat, then all is left is the sending units. but now the question is, do you have good heat in the cab. and if so, all is working except the gauge. you can use a raytech gun to check the heat on the engine at the sending unit. and if the ray tech shows hotter than the gauge is reading then you have a bad gauge or sending unit

[71/454]

The heat is great in the cab. I want to say that I feel the heat cool off as the gauge goes down but I only have how I feel, I haven't actually put a thermometer in a vent so it could be in my head. If I had to guess i would say it's about a 90 second cycle between the movements, so I'm not sure a regular thermometer would catch it. I think I will change the sender though. The fan thing still bugs me, I haven't had time to put in the electric yet.