Radiator issue

poolman · Oct 16, 2020

09 chevy 3500 6.0 runs 210 except at idle SOMETIMES. 50% of the time it will stay at 210 then others it will go up to 230 or so. Get this. Turn the heater on it gets hotter at idle. Replaced the thermostat twice, swapped out temp sensor. Flushed radiator. My local service guy threw a temp gun on it and said that the radiator is partially blocked. IF thats the case whats the best way to flush it? Or just buy a new radiator. If I knew 100% it was the radiator I'd buy one. I think bronco72 put this rad on a couple years ago. Thoughts?

poolman · Oct 16, 2020

Oh and replaced the fan clutch

TBItoy · Oct 16, 2020

seems like the temp gun would tell you how hot it's actually running. How much is a radiator? $100-200? since you've literally threw everything else at it I don't know why the radiator is stopping you.

I'm cheap so I catch the coolant in buckets and strain it through a shop towel an re-use it.

Lil ugly · Oct 17, 2020

have you verified that your water pump is working properly? If the impellor gets corroded or worn it will start to cavitate. This can lead to overheating. The pump wont have any external signs that it is failing. You can use a bore scope to look into the top section of the radiator to see if you are getting any corrosion or plugging of the channels. Usually if its plugged its on the outside from mud etc and can be cleaned with a pressure washer.

extremetownie · Oct 17, 2020

I had a dodge 3500 with the same symptoms. Changed the radiator and i was fixed. You could tell the new radiator was visibly lighter than the old one,i guess the old one was filled up with junk on the inside.

poolman · Oct 17, 2020

Thanks for the replies. A rad was more than that and it's only a couple years old so I assumed thats not it. But if it is the problem is there a better way to flush it out besides the off the shelf stuff?

TBItoy · Oct 17, 2020

I think the "radiator flush" stuff they sell usually breaks looks the scaly rust and oxidation in the block and clogs up the radiator tubes faster.

baldduck74 · Oct 17, 2020

Could the heater core be plugged, and when heats turned on its not bypassing? I'm new to the ls engines

baldduck74 · Oct 17, 2020

Not saying radiator isn't plugged

poolman · Oct 17, 2020

No the heat works great. BUT it gets hotter at idle with the heat on. Explain that????

muddinmetal · Oct 17, 2020

poolman said:
Thanks for the replies. A rad was more than that and it's only a couple years old so I assumed thats not it. But if it is the problem is there a better way to flush it out besides the off the shelf stuff?

White vinegar has always been my go to

baldduck74 · Oct 18, 2020

poolman said:
No the heat works great. BUT it gets hotter at idle with the heat on. Explain that????

I was just wondering about these engines and not being able to just block off the coolant lines when swapped to another vehicle, didnt know if 09s had a bypass valve built into heater hose lines, for when heat was turned off, turn heat on then it pushes coolant to heater core

Lil ugly · Oct 19, 2020

I have not looked at a 09 water pump to verify but on my 2005 6.0l that I put in the buggy I removed the two steel nipples for the heater core and tapped them for NPT plugs. In alot of the other swaps I have seen the two hose nipple just connected together with a short piece of hose. They seem to work just fine like that.