Hey Folks, I’m new to forums and need help with my 98 K1500 truck. I’ve done a lot of work on it, including replacing the heads, gaskets, thermostat, radiator, water pump, fan clutch, fan shroud, and upper radiator hose. Despite all this, the truck still runs hot, reaching 230 degrees at idle and experiencing coolant backfeeding and boiling into the reservoir after it hits 210 degrees. I’m wondering if there’s an issue with the timing or if there’s a way to bleed any air pockets. If anyone has any tips, I would appreciate them.
It could be a bad thermostat, an air pocket in the cooling system, or a bad fan clutch. Also, if the transmission is having issues, it could be putting heat into the radiator (I always use a large trans cooler and bypass the one in the radiator). Is the core of your radiator in good shape? It might be clogged.
@Oli
I just put in a new fan clutch. I don’t think the trans has an issue—it shifts fine, but I’ll look into a separate trans cooler. Any tips on which one to get? Also, I flushed the radiator with two bottles of Code Blue.
@Cameron
Almost any will work. Just get the biggest one that fits. The cooler the transmission fluid, the better.
Oli said:
@Cameron
Almost any will work. Just get the biggest one that fits. The cooler the transmission fluid, the better.
What do you mean by ‘cooler fluid’? Like room temperature?
@Cameron
Exactly, room temperature is best.
What thermostat are you running? And did you put the fan shroud back on?
Kim said:
What thermostat are you running? And did you put the fan shroud back on?
Yep, the fan shroud is new. I don’t remember the thermostat’s temperature setting.
Kim said:
What thermostat are you running? And did you put the fan shroud back on?
Yep, the fan shroud is new. I don’t remember the thermostat’s temperature setting.
You’ll need to know that info. The factory ones were usually 195, so 200-220 isn’t too far off. I’d suggest trying a 160 or 180 thermostat and see what happens.
@Kim
I’ll give that a try. I haven’t changed it yet, and I’m willing to try anything at this point. Quick question: Wouldn’t the thermostat still open if I revved the engine, or is it just about how hot the coolant gets?
@Cameron
If the system can’t get rid of heat fast enough, especially when idling, the temp can go above the thermostat’s setting. Also, check the fan clutch—it might be a mechanical one on that truck.
Kim said:
@Cameron
If the system can’t get rid of heat fast enough, especially when idling, the temp can go above the thermostat’s setting. Also, check the fan clutch—it might be a mechanical one on that truck.
The fan clutch is brand new. I’ll be putting in a new thermostat tomorrow and maybe adding an electric fan too.
@Cameron
I put in a high-flow 180 thermostat in mine, and it works great.
Is it only overheating sometimes? I redid my whole cooling system and had a similar issue. It could be the sending unit.
BowtieBrigade1 said:
Is it only overheating sometimes? I redid my whole cooling system and had a similar issue. It could be the sending unit.
Yes, it only overheats but doesn’t leak. I replaced the top-end gaskets, no combustion leaks. It boils over into the reservoir like it’s pressurized.
Try replacing the thermostat with a genuine GM part.
Jace said:
Try replacing the thermostat with a genuine GM part.
Noted, I hadn’t considered using a GM part specifically.
You can get a vacuum filler off Amazon for cheap and see if that helps. It sounds like it might be an air pocket, but it could be a fan issue if the shroud isn’t on.
Flynt said:
You can get a vacuum filler off Amazon for cheap and see if that helps. It sounds like it might be an air pocket, but it could be a fan issue if the shroud isn’t on.
Shroud is on and the fan clutch is new. I’m thinking about adding an electric fan too.