Engine Temp Low

[Arissett]

So last year I noticed my coolant gauge wouldn’t really ever budge. It’d move if I let my truck idle for awhile but not by much. Just barley touch the lower part of the C. Once the summer came I noticed if I used my ac the gauge would start rising incredibly fast. I never actually let my ac run very long because of how fast my gauge would start moving. We’re in winter now and it’s back to barley moving unless I’m on the road for 20 mins. I just actually was able to look at it’s running temperature and it’s at 145. I’m assuming it’s been like that for the year. I’ve only had the truck for the year and it’s always been like that. I have a new thermostat to replace the old one but I do ask is this the issue or is it a temp sensor? Btw 1999 5.0L V8 Explorer .

 

[Josh P]

A bad or failed temp sensor won't keep the coolant temperature that low. If the thermostat is sticking and won't fully close you would have a cool running engine. Do you keep track of your fuel economy?

 

[Arissett]

A bad or failed temp sensor won't keep the coolant temperature that low. If the thermostat is sticking and won't fully close you would have a cool running engine. Do you keep track of your fuel economy?

Precise numbers? No. Just looking at my gauge? Yes. It’s not really that bad. I don’t drive much everyday. Usually just to work and home and maybe once or twice a week to a friends house. On average I refill every other week. It’s been usually like that. If I drove more obviously the number would dwindle.

 

[Arissett]

A bad or failed temp sensor won't keep the coolant temperature that low. If the thermostat is sticking and won't fully close you would have a cool running engine. Do you keep track of your fuel economy?

A bad or failed temp sensor won't keep the coolant temperature that low. If the thermostat is sticking and won't fully close you would have a cool running engine. Do you keep track of your fuel economy?

Would you know why though if I use my AC the gauge skyrockets? I’ve never watched it move for long as it does move rather rapidly so I always cut the ac before it makes the gauge reach the middle.

 

[Josh P]

Would you know why though if I use my AC the gauge skyrockets? I’ve never watched it move for long as it does move rather rapidly so I always cut the ac before it makes the gauge reach the middle.

I don't trust the factory gauge, it is possible the warm air from the condenser is helping to heat the coolant up if you are sitting in traffic or moving at low speeds. Your coolant temp should be about 40 degrees warmer.

 

[Pete Deering]

So last year I noticed my coolant gauge wouldn’t really ever budge. It’d move if I let my truck idle for awhile but not by much. Just barley touch the lower part of the C. Once the summer came I noticed if I used my ac the gauge would start rising incredibly fast. I never actually let my ac run very long because of how fast my gauge would start moving. We’re in winter now and it’s back to barley moving unless I’m on the road for 20 mins. I just actually was able to look at it’s running temperature and it’s at 145. I’m assuming it’s been like that for the year. I’ve only had the truck for the year and it’s always been like that. I have a new thermostat to replace the old one but I do ask is this the issue or is it a temp sensor? Btw 1999 5.0L V8 Explorer .

When my gauge sensor fail, it stay around C.

Replace the thermostat first. Purge the air out. See if there is a change.
Then replace the gauge sensor if there is no change.

Its sound like, you have air in the upper manifold area.
On my 4.0L there is a Tech bulletin on this issue.
The sensor for the temperature gauge is in the upper manifold.
The gauge sensor could also be bad. The 145 degree is below operating temperature, so the thermostat could be bad.
My gauge goes and stop just below the half way mark. And stay there; if it moves up and down , you have air in the system.
When I had air in the system and the AC was on, the temperature gauge, would stabilize

 

[Pete Deering]

When my gauge sensor fail, it stay around C.

Replace the thermostat first. Purge the air out. See if there is a change.
Then replace the gauge sensor if there is no change.

Its sound like, you have air in the upper manifold area.
On my 4.0L there is a Tech bulletin on this issue.
The sensor for the temperature gauge is in the upper manifold.
The gauge sensor could also be bad. The 145 degree is below operating temperature, so the thermostat could be bad.
My gauge goes and stop just below the half way mark. And stay there; if it moves up and down , you have air in the system.
When I had air in the system and the AC was on, the temperature gauge, would stabilize

After thinking about it. if you have a scan tool. The tool should tell you coolant temp is at the time of the scan. From that result you can make a determination.
1. Is gauge sensor bad?
2. Is the thermostat bad?
3. Is there air in the system?

 

[C420sailor]

Change the thermostat and gasket. Flush the system while you’re at it. Also check your belt and tensioner.

If the additional load of the AC compressor is making the belt slip, the water pump may not be circulating water properly.