I'm with Tootleturtle, I think it's 100% related to the radiator & or block circulation. If it were the head gaskets it would be constant. My truck would do the same thing OEM radiator was leaking, clogged I'm sure and dirty as crap on the outside. Was afraid to wash it for fear of unclogging "another leak". It never held water to within 1" of the neck so it ran low always and when at idle in gear would climb past 185 to 220 plus but never burped. Finally got a good deal at the parts yard on a super cooler, modified the mounting holes and man does that f'r run cool now!! never over 190 "ever"

My guess is his radiator sat(god knows where) & dried out while the engine was undergoing the rebuild and the tossed back in un-flushed when it was time to install. Would be easy enough pop a freeze plug and see if the block needs a flush. "If the radiator flush, wash doesn't do it". I'd buy a set of freeze plugs & some sealant, head to a car wash unless you have a pressure sprayer. Pop one, dig a finger in and decide if the others need to come out for a flush. If so pop them and blast the crap out of the pockets and plop the new set of plugs in "very carefully". Then refill the radiator and remove the return hose(top) from the therm housing and start her up and keep fresh water coming into the radiator cap while running it about 2500 for 10 min. Reconnect the hose to thermo, and see how she does after that,

 

Another low cost item you can do easily is run the fuel tank low and pull the short piece of rubber off and drain the fuel tank into a container obseving the condition of the fuel. Put a gallon or two into the tank and let that drain out. Change fuel filter, again, reconnect and put a few gallons of fresh in the tank.

Fuel tank debris was on the list at the Oregon mechanic. But they did not change the thermostat to a 160 or 180.

 

Ok, so I will tackle the radiator, fan and thermostat. Now I am considering to purchase this radiator...http://www.summitracing.com/parts/BCI-60025/ But I noticed that it does not have transmission cooling. I have a C6...can I run it without cooling or is there a separate small radiator for the tranny? My existing radiator serves the tranny.

 

After reading another thread yesterday, there was a guy with a 360 that he was replacing with a 390.

The 360 had a bigger crank pulley than the 390 did.

So, it is possible to get the wrong pulley on the crank or water pump. I'd make sure you don't have a mismatch, in terms of the water pump pulley being bigger than the crank pulley.

 

Alright so I measured the crank pulley and it is 6.25". I measured the water pump pulley and it is 7.25". What is your opinion? Should I get a smaller water pump pulley?

 

Pit, it sounds like you have the combination that I'd like to try, so I can slow down the water pump and fan. In my winter commuter truck, I want the engine hotter than it is now, I already have a 205 'stat. But most of the trucks I have seen have crank & waterpump pulleys that are the same size or the crank pulley is bigger. It would seem a cheap and easy thing to try, and if it didn't help, easy to change back. DinosaurFan

 

If your going the radiator route, I'd suggest the summit universal one, with the universal mounts, which would be around 200 skins instead of the 500 direct fit one. I used one on my 65 and it works sooooooo much better than the original one.

 

I would definitely try it.

Do you have power steering? Does it work OK when you're not moving?

How about the alternator? Putting out enough at idle that the lights don't dim?

 

Alright guys with all your advice I finally did find a 6.25" water/fan pulley and expect to install it with in a week. I will also flush the system, replace stock fan with flex-a-lite 7 blade fan, replace thermostat to 180. Hopefully this should help. If it doesn't, I will have to invest into an alum radiator. I did notice something that nobody has mentioned...shroud. While looking in the LMC catalog, I did notice that there are three shrouds...one for AC application, one without and one for Tow Package. Is there a big difference between them (like fan size, radiator area, shroud depth) and could the shroud be a culprit?

btw I have AC.

Krewat: PS works well, but does put out an effort while I am at stop. Alternator work 100% without any dimming.

 

If the fan is sitting right in the shroud opening, and the fan diameter is close to the shroud opening, and the shroud itself is in good condition, it should be just fine.

The different shrouds are made for different radiators, fan sizes, etc.

 

pit of pity,

did you ever find a solution? I am facing exactly the same thing as you have, engine stays cool under driving conditions, but heats up during idling. If I increase my revs during idling, it does get colder again. I am suspecting my radiator is blocked, but before replacing it, I would like to know if you have solved your problems?

Thanks,

Bart

 

I've done some work over the winter and I am still waiting for it to really warm up...once it gets above 80 (this weekend I hope) I will test it out. I got a 4 row radiator, changed pulleys (crank and fan) and placed a flex fan. In 70 degree weather, idling in traffic in the sun it hasn't gone above 200F w. 195 thermostat. I'll post any positive results with part numbers fo' sho

 

Hot day in the city. I left it idling in upper 80s for 30 min and temp stayed under 200F. Crank pulley with diameter 7 1/4", fan pulley with diameter 6 5/8", new 4 row brass radiator and flex fan solved the problem.

 

Thanks for reporting back!

 

yes thanks for that, I am going to start with the radiator.

Bart