Help!!! Thermostat, water pump or something else???

[TwoPedal98]

On the drive in to work this morning looked down and temp gauge was at 240 and still climbing, threw the heat on, no heat! Temp hit 260 dropped right back to 170ish (where it usually runs) and had heat again, driving 60mph seemed fine right around 170 got to the center of the next town over soon as rpm's went under 1k started climbing again and no heat hit 260 dropped right back down again had heat kept doing that all the way to work, everytime the rpm's got below 1k shed start climbing, got to work checked it out coolant was a lil low not much quart or less, and no leaks anywhere I could see

98' 5.7 RCLB auto trans 133k on it

Thanks for any help, it's appreciated!

 

[TruckinAin4Sissies]

If you have no heat that means no water is being pushed to the heater core.
Which would make me think Water Pump. However, every pump (that I've replaced) would leak water when it had failed.




-Truckin'-

 

[ChrisAU]

The fact that is was intermittent though tells me thermostat is getting stuck. Try replacing it first, very cheap part.

 

[monstar_est87]

^^^ yea sounds like the thermostat... The water pump would b gushing if it were going out...

 

[oohunter04oo]

If you have no heat that means no water is being pushed to the heater core.
Which would make me think Water Pump. However, every pump (that I've replaced) would leak water when it had failed.




-Truckin'-

X2 about no water through the heater core, which probably means you were low of coolant. I would top it off and pressure test it.

 

[TruckinAin4Sissies]

How's the belt?




-Truckin'-

 

[TwoPedal98]

Thanks guys! Gonna top it off (not low by much tho) and pull the thermostat out, and hopefully that's it or I can at least make it home so I can screw with it there, never had a pump or thermostat fail like this before, it was always all or nothing or the leaky pump

 

[TwoPedal98]

How's the belt?




-Truckin'-

Some small cracks but all there and working

 

[TruckinAin4Sissies]

Also check your oil.
Check (with a flashlight) around your intake manifold for leaks.




-Truckin'-

 

[DGA1]

Usually when you turn the heater on and get no heat out of it, it's that you have an air pocket in the system and the air is stuck in the heater core. Inversely if the temperature goes down when you have the heater on (and it blows out hot air) you have an air pocket somewhere. You are losing coolant somewhere, or lost some somehow, but in the end need to top it off since you are probably low.