Thread: 250 degree temp under load

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First, the facts
1970 Nova
th350 w/shift kit
95 2 blot main short block
world s/r torker heads
isky 270 cam
edelbrock performer intake
pete jackson gear drive
holley 850
manley guides and valves
3 row aluminum radiator w/ 16" electric fan
8 qt moroso oil pan
moroso high volume/ high pressure oil pump
15" ralley wheels

After I put this motor together, i had an oil pan leak. I had used the one piece seal from felpro. I lifted the motor up enough to get the pan off (along with removing the steering linkage). I removed and replaced the seal with another one piece from felpro. I finished after dark so I couldn't read the temp guage. On the way home, there was a good sized BOOM along with a lot of smoke. The motor shut off. I finally got it restarted (in the dark) and got to the nearest gas station. I saw the distributor was not completely down. I assumed that was the problem, fixed it, and got home. I usually run around 190 degrees, but it started running hot. My aluminum fan had quite a few holes over the years, which I "fixed" with bars leak. I changed out the old two core for a new 3 core and larger fan. I also changed to a 165 thermostat.

Prior to the changing of the oil pan, I had no overheating problems. After I changed out the radiator, it was still overheating, only when picking up speed or under a load. I could stop and let it idle and it would cool right down. I susected a blown head gasket. I had it tested and they found C02 in the overflow tank and said it was a blown head gasket. I spent the last two days changing out the head gaskets. I filled up the fluids and went for a test drive. Nothing changed. I get up to 250 degrees rather quickly when I am going over 45 mph or when I climb a hill. As soon as the load is taken away, it cools back down.

Any Ideas?

Originally Posted by 1bigdually

First, the facts
1970 Nova
th350 w/shift kit
95 2 blot main short block
world s/r torker heads
isky 270 cam
edelbrock performer intake
pete jackson gear drive
holley 850
manley guides and valves
3 row aluminum radiator w/ 16" electric fan
8 qt moroso oil pan
moroso high volume/ high pressure oil pump
15" ralley wheels

After I put this motor together, i had an oil pan leak. I had used the one piece seal from felpro. I lifted the motor up enough to get the pan off (along with removing the steering linkage). I removed and replaced the seal with another one piece from felpro. I finished after dark so I couldn't read the temp guage. On the way home, there was a good sized BOOM along with a lot of smoke. The motor shut off. I finally got it restarted (in the dark) and got to the nearest gas station. I saw the distributor was not completely down. I assumed that was the problem, fixed it, and got home. I usually run around 190 degrees, but it started running hot. My aluminum fan had quite a few holes over the years, which I "fixed" with bars leak. I changed out the old two core for a new 3 core and larger fan. I also changed to a 165 thermostat.

Prior to the changing of the oil pan, I had no overheating problems. After I changed out the radiator, it was still overheating, only when picking up speed or under a load. I could stop and let it idle and it would cool right down. I susected a blown head gasket. I had it tested and they found C02 in the overflow tank and said it was a blown head gasket. I spent the last two days changing out the head gaskets. I filled up the fluids and went for a test drive. Nothing changed. I get up to 250 degrees rather quickly when I am going over 45 mph or when I climb a hill. As soon as the load is taken away, it cools back down.

Any Ideas?

A blown head gasket can be tested for without chargning into swapping gaskets but you are past that point...

Check your oil and coolant, condition and levels. Oil will turn a milky green if there is antifreeze in it and antifreeze will get dark and slimier with engine oil mixed in. If your coolant level is too low you can experience flash heating issues, but your cooling system may be "saving" you

Tell us about your electric cooling fan, how is it controlled?
Do you have a water temp gauge or just an idiot light and where is the sending unit installed?

Regarding your thermostat, 165 is quite low... I would think 185-195 would be better...

Not sure about the big boom you mention, need more details to "guess" but usually there are consequences of such noises. Have you done a compression test on that engine since the boom?

Is the fan a pusher or puller, and what CFM is it rated at??? Are you running a shroud?

i had a similar oveheating problem in my tudor.. after trying a few things, I was ready to replace the old brass rad I have. luckily before I did, I brought it to the radiator guru in our town. he did a complete flush. Turns out a F$%#ing mouse had built a nest while it was off the car last winter. a cool 195-210 tops since. did you change anything that could be blocking a water passage?

Lower radaitor hose collapsing?

Quote.........My aluminum fan had quite a few holes over the years, which I "fixed" with bars leak. I changed out the old two core for a new 3 core and larger fan.


On the way home, there was a good sized BOOM along with a lot of smoke. The motor shut off. I finally got it restarted (in the dark) and got to the nearest gas station. I saw the distributor was not completely down. I assumed that was the problem, fixed it, and got home. I usually run around 190 degrees, but it started running hot.

Not trying to beat up on you but not one of these statements makes a dang bit of sense. No way did you fix an aluminum fan with Bars leak ?????
With the boom did the smoke come from under the hood ????
Where was the temp before the Boom ???
Where was the oil pressure at????? Because if the distributer was not seated as you state then it could not be engaged into the oil pump !!!!!
Although your statements make no sense to me heres my take on your overheating at speed. Radiator could be partially clogged, to test take a digital temp gun with the engine warmed up fully and take temp readings all across the radiator core,they should be fairly even, If it shows colder at bottom of core it usually means its a clogged radiator. Or as stated you could have a lower radiator hose sucking shut,it should have a wire spring in it to prevent that. Or is the electric fan moving air in the right direction ??? it should be blowing the air towards the engine bay depending on wich side of the radiator its mounted and if its a pusher or puller fan. I,ve found them mounted backwards and I.ve found them wired wrong so that they where running backwards,regardless it has to move the air towards the engine.
Hope this helps you.

I am not an expert but from past experience this has happened to me. (1.) Once while priming a friends car with gas down the carb (aloong time ago) I got some gas on the disti and it leaked down the shaft. When cranked blew the oil fill cap off like a mortar. (2.) Last Feb. (more recent) I replaced an engine in a 98 Z71, 350 vortec, FI. All went well but noticed every morning the lower hose was collapsed (no spring either). After getting on this site and talking it thru discovered the hose to the overflow tank was clogged. The system was not open to the atmosphere. Hope something helps.