1998 k2500 454 getting hot

[newguyinnc]

Hey all, have a 1998 k2500 with gen6 454. Bought the truck and immediately noticed it would get hot. 235° , but not boiling over. Changed radiator, water pump, thermostat, fan clutch, upper and lower radiator hoses, and flushed the system twice. Even pulled the lower block drain plugs and flushed it that way. Still got hot. Decided to have the motor completely rebuilt. Same issue. It now currently has a proffessionaly rebuilt original motor, new aluminum 4 core radiator, water pump, 195° thermostat, fan clutch hoses, thermostat housing , fuel injectors, and fuel pressure regulator. It'll drive around at around 215° , when you stop for a light or get off an exit off the highway, it will climb to 235°. Once you take back off, it will go back down to 215°. Cats were checked with a sniffer ant local exhaust shop and all sensors under the hood were changed when motor was reinstalled. Gauge was double checked against a mechanical gauge before motor was pulled to rebuild. Thinking there's a block in the motor preventing full flow in the cooling system, but entire engine was hot tanked when rebuilt. Scratching my head at this point. Any ideas on which direction to go from here??

 

[454cid]

That's a lot just to chase after a cooling issue. Do you have the stock fan shroud installed?

Is the water pump, the proper pump for use with a serpentine belt? The serpentine belt require a reverse rotation pump. If you somehow got a pump for a v-belt application it's being turned backwards and won't pump well. The differance is in the impellers.

 

[Keeper]

Is it losing coolant? Cap not holding pressure?

fyi - my L29 likes the 180 thermostat.

 

[618 Syndicate]

What are you basing the temp on?

 

[newguyinnc]

The radiator has the factory shroud in good shape. No coolant loss and cap is holding pressure. Verified the dash gauge was correct with a mechanical gauge installed before having the motor rebuilt. From a cold start, it will warm up to 200° and you can see on the gauge when the thermostat opens and the temp drops to around 160-170°. After the thermostat cycles the first time, the engine warms up to 215° and stays there while the truck is moving. Stop at a stop light for more than a few seconds and the temp starts to climb to as high as 235°. Once you get moving again, it'll drop back to 215° pretty quick.

 

[newguyinnc]

The mechanic and I both thought it was a lean condition because bank 1 and bank 2 long term fuel trims weren't even close and it didn't seem like the timing was getting enough advance on the scanner at higher rpm. That's why we did the injectors and fuel pressure regulator. Advance and fuel trim is right now with the new injectors, but the cooling issue still persists.

 

[newguyinnc]

Is the proper water pump as well. First new one I put on lasted 50 miles before the hub came loose on the shaft and sent the fan into the radiator. Installed another new pump along with a new radiator. Forgot to mention the a/c condenser is new as well.

 

[618 Syndicate]

Just because the gauge worked before the rebuild doesn't mean it still does. I'd verify it again.

 

[newguyinnc]

Just because the gauge worked before the rebuild doesn't mean it still does. I'd verify it again.

I originally thought the problem was the temp sensor in the head. Changed the temp sensor and got the exact same readings. Pulled the sensor out entirely and put a brand new mechanical gauge in the head and still had the exact same readings under the same driving conditions. The sensor we put in the head after the motor was rebuilt is the same new one that I verified against a mechanical gauge that I know worked. None of these parts have over 150 miles on them.

 

[618 Syndicate]

There are two temp sensors, one for the gauge and one for the PCM. I don't remember which is which offhand.