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Check gauge light - 1994 Chevrolet 1500

My “Check Gauge” light came on in my 1994 Chevy Silverado this morning. it was about 32 degrees with frost on my windows. I warmed the truck up be heading to work. As was driving up I-5 about 2 miles into my drive i noticed the “Check Gauge” light. I checked gauges and my temp gauge was full into the “red zone”. A little panicked I turned the heater off. the gauge slowly returned below 200 degrees. I then turned the heater back on. At a STOP, I head some gurgling behind the dash.the temp. gauge seemed to remain steady from the short period I turned the heat back on. finally I got to work, shut the truck off and the gurgling continued. What could be the problem?

Air in the coolant? Is your coolant level in the radiator low?

Thank you. I just checked radiator no fluids. Did I cause damage? Should I have mechanic look at my truck?

Can not guess on whether or not damage was done.
But yes, it should not be driven. There is one or more leaks in the cooling system. May only be a hose, but could be the radiator. But you need to have it repaired or you will cause extensive damage.

I just hope for the OP’s sake that the leak is only the result of an aged hose, or a rusted-out radiator, and not because of a breached head gasket or intake manifold gasket.

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The heater core is inside the cab on this model . . . any gurgling you heard may have been coming from that area

Is there coolant inside of the cab, such as on the passenger side footwell? If so, your heater core is leaking. But it’s super easy to replace.

You might want to consider putting the truck on jackstands, filling the cooling system with water and letting the engine idle while you look for leaks. It could be something as simple as a water pump or a bad hose

I presume you intend to fix the problem(s) yourself . . . ?

5.7 engine, the overflow coolant is under hood near dash of passenger side. Why would the temp go down after I turn heater off? Is that the possibility of heater core?

Do you mean it’s leaking coolant under the hood, near the dash, on the passenger side? That is right in the area of the heater core. There should be two smaller coolant hoses going into the firewall (leaving the engine compartment, going into the cab). The heater core is on the end of those hoses, inside the cab, under the dash. If it is leaking in that area, make sure it isn’t leaking from the hoses. If it isn’t the hoses, may well be the heater core. Very difficult to say for sure without actually seeing exactly where the coolant is leaking.

I think the fact that the temp went down when the heat was turned off is probably more of a coincidence than anything else, though. I believe coolant circulate through the heater core whether the heat is on or off in those trucks. Generally if the heater core is leaking badly, you will find your passenger floorboard is getting wet with coolant.

I’ve had cars where the best thing to do when they were starting to overheat was to turn on the heat. That way the coolant circulated through the heater core, which acted like a supplemental radiator. We drove across Nevada on a hot summer day with the heat on in a mid 60’s Mercedes 190 sedan. That wasn’t fun at all.

You seem to have a different problem. If you’re lucky the problem is your radiator cap is worn out and can’t sustain pressure. That’s really lucky. More likely you have a leaky hose or a failing water pump.

Thank you. It is odd that the temp cooled after heater was turned off. Mmmm!

The gurgling is most likely caused by air trapped in the cooling system. As the air bubbles go through the heater, tends to make a that sound and is usually quite audible in the passenger compartment. Normally a cooling system doesn’t lose more than one or two cup of coolant every 6 months. Since you are losing much more than that, best to tow the vehicle to a shop and let them do the diagnosis. When you turned the heater to “off” it probably eliminated the coolant flow through the heater core, so even though it was low on coolant, more coolant was left to cool the engine. You are right, usually when turning on the heater and fan to max heat, that will cool the engine a little. But it only works if there is plenty of coolant remaining in the system. Best of luck.

Thank you. You conclusion was exactly right. My coolant was low. I took my truck to my mechanic, he replaced coolant. Yet, he was not sure why the engine cooled when I turned heater off. I really appreciate all the advice. I will keep this in my files and share this with others.

Glad you got that pesky cooling problem under control. Best of luck to you.