Overheating

[MrSchaeferPants]

So my CUCV's temp dummy light always comes on when driving.

84 cucv, with a 350 from a 77 Jimmy

Before I did all the work, it never over heated.

I put in a cam, lifters (stock), at the same time a new waterpump, thermostat, all related gaskets of course. It has a new upper and lower radiator hose as well. I also flushed the radiator before I did all the work.

So now that's all done, been driving it. But the dummy light always comes on and I can't figure out why. It doesn't "seem" hot. In the driveway when the thermostat opens I can feel the heat difference from the fan blowing the air, and after a few moments, I can feel the air cool down. So I'm assuming that all works fine. Best of my knowledge there's no air trapped anywhere.

I'm also wondering, since it was a diesel, would the temp sending unit be different enough where the dummy light would come on at a different temperature because it's reading the 350's sending unit instead of the one on the diesel? Because like I said, driving around, and when I park and pop the hood, it doesn't seem overly hot, it doesn't smell like it's overheating at all.

 

[dyeager535]

Is it a switch for the idiot light, or is it a sending unit for a gauge?

 

[K5_Fla]

correct rotation on new water pump ?

 

[ktmoutfront]

If it were my truck, I would buy a gauge with a sending unit. the dummy light only says "hey dummy, its hot". You don't really know what is going on. Even a cheap gauge is better than a light.

 

[MrSchaeferPants]

Is it a switch for the idiot light, or is it a sending unit for a gauge?

Not sure what you mean. Normal sending unit on the driver's side of the block.

correct rotation on new water pump ?

Yes

If it were my truck, I would buy a gauge with a sending unit. the dummy light only says "hey dummy, its hot". You don't really know what is going on. Even a cheap gauge is better than a light.

I have a parts truck with all the gauges I want, but would the gauge set/dash bezel circuit board and plug be the same to just swap?

 

[ktmoutfront]

Not sure on the swap. I bet somebody will chime in on it.

 

[K5dreamer]

faulty temperature sensor? should be an easy/cheap thing to swap and see if it fixes the problem.

 

[dyeager535]

Not sure what you mean. Normal sending unit on the driver's side of the block.

If you have an idiot light, there is a switch that is used, not a sending unit. I've never dealt with the idiot light switch, but I know that using one in place of the other will cause problems.

 

[MrSchaeferPants]

If you have an idiot light, there is a switch that is used, not a sending unit. I've never dealt with the idiot light switch, but I know that using one in place of the other will cause problems.

I'ma guessing. the cucv has dummy lights, the 77 jimmy that the 350 was out of had temp gauge, so the sender on the block is a regular sending unit. No idea about the switch thing, diesel block is long gone so I have no idea what it would even look like. I've always had gauges, so the dummy light is new to me as well.a

The part that makes no sense is it wasn't always like this. But perhaps it was just time for the sending unit or whatever to go bad. As far as testing the sending unit, it should be some sort of ohms test, but I've been searching and can't figure out how. Other than reading 0 or infinity meaning it's bad. where do I put the leads, and what numbers read good cold and hot.

 

[Fordum]

Gas gauges on GM seem to be almost all 0 to 90 ohms, but if that carries over to temp sending units, I have no idea.

If you have a gauge sending unit hooked up to a light, the light will either start out bright and get dimmer as the engine heats up, or start out dim or out and get brighter.
Depending on how the sending unit goes.

Either way, if you take off the one wire to the sending unit, and hook an ohmmeter to the post and ground, it will tell you something.

Since you have a light, if you get anything other than infinity, open circuit, with a cold engine, then its wrong.

Either you have a gauge unit, or a partial short in the sending unit. Does not really matter which, its wrong.

To be honest, I feel there is only two ways to go.
Either leave the light, and buy a light type sending unit, or better yet, replace the sending unit with a mechanical gauge.

Electric gauges work, but if you are going to go to the trouble of installing a gauge, go first class.
Almost always more accurate, and more reliable.

 

[MrSchaeferPants]

I'll try the ohms test the way you said to do them

better yet, replace the sending unit with a mechanical gauge.

On that note specifically I didn't even know I could do that, or rather that was available. Of course I've had/seen mechanical oil pressure gauges. I didn't even know of an analog temp gauge. Looked it up as I'm typing this. By the pictures, they look like a thermometer (in a sense) I assume screw into where the sending unit does.

This isn't one I plan on getting, just found a picture/product. But this right?
http://www.summitracing.com/parts/SWW-82480-72/

 

[Fordum]

Exactly. They have a tube and bulb filled with liquid, and the temp gauge is basically a pressure gauge calibrated to the expansion of the liquid and marked with temp.
As the bulb in the engine heats up, the liquid expands, and the needle moves. Simple, and accurate.
You simply unscrew the present sending unit, and screw in the new gauge's probe.

AFTER threading the thin tube through the firewall and anything else it has to go through.

Its very common to get it all hooked up, only to discover it has to go through the mounting bracket first.......

As for what to do with the gauge its self, someone else will have to give you ideas. Quick and dirty, is to get a chrome or stainless steel bracket that the gauge fits, and mount it where you can see it.

Older trucks often just mounted it to the bottom edge of the dash.

I would be willing to bet someone here has found a gauge the right size and managed to mount it in the original location in the dash where the factory light/gauge was.

But, either way, mechanical is nice. The only power you have to worry about is a single wire that hooks to the dash lights to power a built in light.
It is pretty much foolproof, and reads all the time, not just when the key is on.