Skip the auto shop - Our mechanics make house calls

Q: 1998 GMC keeps overheating on the temperature gauge. It's full of water and has a new thermostat.

asked by on

What's causing truck to overheat

A: Hi and thanks for writing to YourMechanic. ...

Hi and thanks for writing to YourMechanic. There are several things to look at. First off, have the coolant tested and make sure it is within spec. If coolant is not mixed at the correct ratio, it can cause the engine to overheat.

Second, being that your truck is a 1998 there is a possibility of a water jacket getting obstructed, not allowing proper coolant to flow and cool the engine.

In this case a coolant system flush can cure this problem. Check and make sure that the radiator fins are clean and clear of any debris. Not enough air flowing through the radiator fin will also cause overheating.

Finally, there could be an electrical issue. The water temperature sensor might have corrosion which acts as resistance and will read high temperature. In this case, the temperature sensor switch will need to be replaced. You will need to have the coolant temperature electronic system checked for resistance and/or any broken/bare wire. If you would like to have this taken care of, a qualified pro from YourMechanic can come to your car’s location to inspect the overheating problem and proceed with the proper repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Luke warm heat from heater

This may be a thermostat issue where the thermostat is not closing at the right temperatures resulting in the coolant running continuously throughout the motor which does not allow the engine to reach normal operating temperature. As you may know,...

Q: Van overheats at idle, temperature jumps and then drops

Check to make sure the fan clutch is working by getting the van warmed up good and using a tissue in front of the radiator center have someone raise idle to 2000 rpm and put tissue on the front of...

Q: Car is losing power and the temperature gauge reads high.

Hello. From what you've described, most likely, your engine has had a head gasket failure, perhaps because of a failed thermostat - which could cause the "temperature way up, then backs off" cycle you describe. A failed head gasket means...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.