Coolant Temp Issues

Hi all. Driving an ‘02, 5.3 w/ almost 300k on the odometer. As to be expected, I deal with my share of “quirks” here and there. For quite a while now I have gotten used to the “low coolant” message flashing up on the dash… even tho a quick check at the overflow shows the coolant level to be perfectly full. Out of nowhere this morning I noticed the temp gauge moving up from its usual 210 mark steadily toward the red. I pulled over to a stop and before I could even put the truck in park the temp started moving steadily back down to normal. I limped home using this stop and go routine to keep the gauge from spiking. Basically, foot in the gas = higher temp / out of the gas = drop in temp. Engine bay didn’t seem to be excessively hot when I got home, but I did seem to notice a bit more “gurgling” from the coolant system than I would have expected. Any thoughts?

Also, similar issue with the oil. Constant dash alerts to low oil levels, even tho I am constantly checking that as I seem to burn about a quart every couple weeks. Had rear main done about a year ago and other seals/gaskets as well as a heavier sending unit done shortly after that. No signs of leaks anywhere. Also the oil pressure will sometimes rise/fall significantly in line with driving or idling. Does this seem normal for a truck this old or maybe indicative of another problem?

Verify coolant temp with a IR gun. If its good then suspect bad sensor, temp gaueg or wiring issue to sensor. Have you been needing to add coolant to the system over the last 4 months or so? If so then you have a leak and likely have air in the system which can explain the gauge moving so abruptly. Was your oil low when the dash said it was? If not then sensor or its wire has a problem. Not likely to be a gauge problem since they dont tend to work correctly and then not and then heal themselves. They usually just fail or continuously show incorrect readings.

Jeremy4601 said:

For quite a while now I have gotten used to the “low coolant” message flashing up on the dash,
even though a quick check at the overflow shows the coolant level to be perfectly full.

Click to expand...

Before reading further, this would point to a faulty coolant level sensor, no?

Jeremy4601 said:

Out of nowhere this morning I noticed the temp gauge moving up from its usual 210F mark steadily toward the red.
I pulled over to a stop and before I could even put the truck in park the temp started moving steadily back down to normal.
I limped home using this stop and go routine to keep the gauge from spiking. Basically, foot in the gas = higher temp / out of the gas = drop in temp.
Engine bay didn’t seem to be excessively hot when I got home, but I did seem to notice a bit more “gurgling” from the coolant system than I would have expected.

Click to expand...

I actually suspect your H2Opump may be failing.
If it's not pumping well at lower RpM, maybe this is causing momentary hot spots / air pockets
until the coolant flow increases by enough to flush liquid coolant through the hot spot?

When was the last time you checked your hoses? Flushed and changed your coolant?
Please don't say over 3 years ...

Jeremy4601 said:

Also, similar issue with the oil.
Constant dash alerts to low oil levels, even tho I am constantly checking that as I seem to burn about a quart every couple weeks.
Had rear main done about a year ago and other seals/gaskets as well as a heavier sending unit done shortly after that. No signs of leaks anywhere.
Also the oil pressure will sometimes rise/fall significantly in line with driving or idling.
Does this seem normal for a truck this old or maybe indicative of another problem?

Click to expand...

Are you using a PCV 'Valve'? If so, you should be using 12572717, which is more like a whistle.
Oil pressure is absolutely a function of RpM.
Under 10psi per 1000RpM is cause for concern, regardless of GM's lowball specs.