Thread: run hot on idle

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I finally got to the point of breaking in my engine (350); ran it for 25 minutes, at 1800rpm. RAN GREAT! No problems. No leaks. Temp stayed right at 185, until I brought it off the high idle. While I was messing with the idle mix screws on the front of the carb, the temp jumped right up. I shut it off at 210. This only took a minute or two to move up that fast. I checked the oil and its about 1/2 quart low, but I did not wait to see if more would drain down into the pan after turning off the engine. When the block was done at the machine shop, it was already bored out to 40 over, and the machinist took it to 60 over. Someone did say it could have heat issues at 60 over - but I did not think this type of spike is what they were speaking of. The radiator is fairly new, but it is whatever the original was - single or double core? Do I need a bigger radiator? I thought that I had let the car run enough prior to breaking it in, to "burp" the radiator. The timing is about 9 - 10 advanced. I do not have electric fans on the radiator, but the engine fan seemed fine at the higher rpm. Any thoughts?????? thanks - kip

Couple of thoughts. If the temp shot up that quickly it could be just hot water that was in the block moving to the area where your sender is and giving you a temporary reading. The other thing is that 210 isn't all that high, did it want to go higher? Could also be an air lock in the block.

Do you have a shroud on the mechanical fan? I'm really a fan (no pun intended) of electric fans with a good shroud, especially for the low speed cooling ability.

Start it up and see what you get this time.

Don

I've checked the fan clutch and it seems fine. The car does have its fan shroud on it. It almost seems as if, it did not get water when the engine began to idle. Can this be an air issue in the water system? I guess I can let it run on idle, with the radiator uncapped and watch for water movement and air???? thanks - kip

Sometimes you have to burp an engine. Hondas have a bleeder valve on top of the engine for this reason and if you don't do it they overheat.

There are lots of unknowns here. What kind of car, what water pump, what kind of radiator, did the car run hot before the rebuild, etc.

Don

Its a sbc 350, in a 77' corvette, with a 60 over bore, an L82 cam, running off the center carb of a tri carb system, the car did not run hot before, and the shroud is in place. I'm putting the other carbs on now that the center seems to be set, and will run the car at idle, with the radiator uncapped to watch for movement of water and air escaping. I did not let the car run long enough to see if it would have dropped after the 210 was reached... if the radiator seems ok, I'll cap it and let is run to see what happens... thanks - much, kip

Don's right about 210 not being that hot, even 220 is not that hot when properly set up with a 50/50 mix of coolant and water. 245 can be safely obtained before a serious problem erupts. The first thing I would recommend would be to make sure all of the air is out of the system and then run and test it again. An air bubble block can cause overheating problems. But then again 210 is not overly hot.

I had a very similar problem when I first started driving my 32 roadster with a .060" over 350. Let's just say that I tried everything I could think of without any success. I now have driven it 8,000 miles with a unvented solid three piece hood, and hardly ever turn on the electric fan unless stuck in bumper to bumper traffic.

My cure was that I finally "discovered" on my pretty "no name" imported polished aluminum water pump that the impeller (I took the back of the pump cover off) was not even close to the pump casting, effectively pumping no flow of coolant. I bought a FlowCooler pump and never had another cooling problem. The fix is not always easy to see. Good luck.

Interesting you should mention that. I had the same problem with the 302 in my '27 when I first got it running years ago. I took of the nice chrome waterpump and put a flowcooler on it and the problem went away.

Don

Thanks for the info. I intended to burp the engine, but when I went out to do so, it would not start. My guess is that the module in the distributor is bad, in that there is power to a new coil, but no spark...

I do have another question concerning three dueces. The set I have, only has idle mixture screws on the center carb, the 1st and 3rd, are sealed off, thus the engine only idles on the center carb. Someone has told me the reason I'm also having a problem getting the car to idle well, is that all three carbs should have idle mixture adjustments, in that a 350 will not idle off only one carb???? Any ideas? Seems the carb sets I seen advertised come with the 1st and 3rd carbs sealed off.... thanks for the help - kip

I don't mean to pirate the thread but I have searched for a specific thread and at the moment do not know how to start a new thread on "mechanical radiator fan". I have a 0.030 SBC 350 that came out of a '76 Corvette and it only has a cam essentially like the stock '77 Z28 and I am just now installing a Walker 487-1 Model A radiator in a '29 fendered 'glass body. I have previously studied the installation of an electric fan by Brian Rupnow in his "Wild Canary" A RPU with a SBC 305 and I was not happy to find that the electric fan draws some 70-90 amps on startup and maybe 30 amps when running. I had hoped to use just a mechanical fan with flex blades and a shroud, but the tech guy at Walker was very discouraging about the fact that the water pump (short) is so low on the radiator in the Model A that even a small 15" diameter fan will just come down to the bottom edge of the shroud and so will lose the benefit of the shroud on the bottom. I have thought of using a 15" diameter fan and pop-riveting a 1" lip along the bottom of the shroud to recover the air path of the shroud. I have already learned that there is a lot of waste in trial-and-error attempts in building a rod from scratch so maybe I just have to try that and then scrap that idea and go to an electric fan. Still I would like to avoid an electric fan and maybe the mechanical fan with a better water pump would work? My question is specific to a SBC in a Model A so it is outside the main thread here but is related to a Vette-SBC and I have already learned about the possibility of a better water pump, so thanks for that. Any helpful comments will be appreciated.

Don Shillady
Retired Scientist/teen rodder

If it run cool under power and over heets at an idel you have the vacum advance line on ported vacum. So when ideling it is retarted. Move line to constant vacum and check dist to make sure both advances are working...Good luck Jim

The 383 cu.in. engine in my 74 corvette coupe ran at 210 degrees until I installed a 160 degree themosat and replaced the old tired clutch fan with a flex fan. I know that there are many who say the flex fans are trouble but I and many others have used them with great success and no problems. My engine temp never rises above 190 degrees and I run my coupe hard. If you are trying to keep it original this of course will not help you.

Don-you can raise your fan 5" and it will not be any longer than a short http://www.parts123.com/parts123/yb....Z5Z5Z50000042b If you can't find it look up Parr automotive. VERY COOL LOOKING

Langen and Rgtrough, thanks for your suggestions. I finally found the Zip accessory at Southern:

http://www.southernrods.com/categori...duct-1845.html

Maybe Parr doesn't stock them anymore. I am still mulling over the cost since on another thread C9X shows he runs a 455 Buick with a low flex fan in Arizona! I think I will change to a 160 degree thermostat along with a max-flow low pump. Sadly I usually end up trying three or four things in my expensive "development program". I used to wonder where all the stuff comes from for swap meets, but now I have a better understanding of all the stuff that folks "try" along the way.

Don Shillady
Retired Scientist/teen rodder