On my 92 f250 with a 5.0 I'm having a low coolant temp problem. Maybe it can be considered "under heating"? I tried searching and didn't get what I needed. Now, I was driving and looked down at my temp gauge and it was fluctuating between being bottomed out, and 1/4 way up. Usually, it's at half or lower once fully warmed but it never got that high during this issue I am having. So, I thought maybe I was low on coolant. I stopped at a gas station to check it but when I went to open it some coolant sprayed out (usually when it's low, I can still open it considering it was only running for a few minutes). So then I filled the reservoir up instead. On the way back home it still moved around a little but not much and still didn't get high. SO this morning I looked at it, took off the radiator cap (engine off) and it was full to the top. I started it and it never really dropped much. I managed to get some water in but it's not able to take anymore. But my gauge STILL fluctuates and on top of that, I have great heat. I had the radiator cap loose while it was running and even drove it to see if it would burp any air out. no difference after that. It doesn't seem to build much pressure either. I changed the temp sensor (yes, the one for the gauge and not the ETC) no difference.

My 3 ideal possible causes:
Radiator Cap faulty (it's less than a year old but that doesn't mean much)
Faulty/sticking thermostat (Replaced about 3 years ago and it's the OE style)
Poorly mixed anti-freeze?? Could not enough water do this?

Like I said, great heat, topped off coolant (mind you, I've been through quite a few coolant system burping on this truck and it always burped itself out quick) and the temp is extremely low especially when I start driving. Any suggestions????

 

I am paying close attention to this, as I have EXACTLY! The same issue with my 95 with 5.0

Runs great, but seems to be eating a little more fuel these days

I changed the temp sensor right by the thermostat, is that the gauge unit? Or where is the sensor for the gauge?

 

The sensor for the gauge screws into the intake manifold and has only one wire that slips over it. It's located right behind the A/C pump area. I'm sure someone on here has a picture of it's location. Have you tried changing anything else to fix this temperature problem (Thermostat, cap)?

 

Sounds almost like the fan it's self...The Fan Clutch....

In reverse though....

 

Ahh. I will have to check that.

My issue started when I replaced just about the entire cooling system. Rad had a pin hole, and waterpump died at 120,000 miles. So new radiator and water pump with a new cap and thermostat. All of it was supposed to be stock replacement parts. I did have a while where I was topping up the coolant, so now I get some rusty sledge in the top of the radiator, but it is working its way out.

So I have not tried anything else yet. I still have te old cap I may try as well as maybe another new thermostat. About 11 to the gallon is not quite right

 

get a gauge that has some numbers first and then take it from there.. these factory gauges are bunk. (accept speedo and tack lol)

 

just a thought.......Could the thermostat be turned the wrong way by chance? Just a thought...
The Voltmeter is also good....it's the Oil pressure gauge that is the idiot light...Simply goes off at around 5-7psi.....

 

I did check the temp using a voltmeter. It jumped around then too

 

Ok so anyone know what the rad cap and thermostat should be?

I'll check mine. Also what is the correct orrientation for the t-stat? I seem to remeber putting the longer side into the block side.

 

IIRC, radiator cap should be 16psi...

The T stat should be a 195*

 

16 PSI? MY cap says 13 on it. I wonder if that's my problem. hmmm

 

The way I see it, if you have the correct temperature thermostat and that thermostat is working properly, there is no way the engine can run too cold. One exception might be extreme cold conditions. If I'm full of it, someone please put me in my place.

 

It's not really been extremely cold here. But I was wondering if the spring on my Thermostat was weak and opening too soon, or it was maybe stuck open a little. But I'm really confused because I have great heat. I'm starting to wonder if my gauge is messed up even though I tested it with a voltmeter and put in a different sender.

 

If I was really concerned about my engine temperature I would get one of those temperature readers that you point at something and it gives you the temperature. Don't get a real cheap one. Probably the best place to point this would be close to the thermostat housing on the intake manifold. With a 195* thermostat I wouldn't expect a reading higher than 185*.

I should also mention that the heater will take a certain amount of heat away from the engine. It's like a mini radiator and it of course bypasses the thermostat. You would want to turn the heater off if you do this.

 

I just thought of something... So my gauge fluctuates like it has an air pocket. I've made sure it doesn't have one. I think it's my thermostat but that thought is changing. Now, if my gauge is fluctuating, shouldn't the heat coming out of my vents fluctuate too? Because the heat is amazing and I haven't felt it fluctuate. Maybe my gauge really is bad.

And, I think I can get a hold of one of those thermometers that 88n94 mentioned and do exactly what he said. I know someone that works on HVAC and should have one.