I have an overheating problem I’m trying to work through and could use any and all thoughts on the subject. Car is a 1969, 427 Tri-Power. This project has been a complete frame up restore.

Engine: 427 w/ Edlebrock Alum heads, solid cam, 10.5:1 compression, Tri-Power. All parts with the exception of the Intake, Block and Rods are brand new out of the box.

Radiator: Original 427 that I had re-cored

Heater Core: Brand new

Thermostat: 160 degree

Expansion Tank: Brand New

Fan Clutch: Brand new

Water Pump: Brand new GM Alum water pump.

Water Pump Pulley: 1968 427 or so I was told.

I started this engine in the frame before I put the body on and the Temp was running about 180-210 with a box fan in front of the radiator and using a mech. temp gage. Once I put the body back on and re-installed the radiator, fan shroud and everything else I fired it up and now my temp (using electric gage in car) goes to 250 degrees (pegs out) in about 3-5 mins. I shut the engine down and waited about 30 mins and the gage was at 130. Started the car up and within a few mins the gage went back to 250. The Heads are hot but not too hot to touch, radiator is cold, intake is hot, and water in expansion tank is hot but again no too hot to touch.

Here is what I have done so far and observations I have made.

After adding 1 gal of anti freeze and 2 gal of water I installed my re-fill kit and pulled about 22-23 HG In of vacuum. Opened the re-fill valve at this point and got about another 2-3 gal of water in the system. So I’m sure there is about 5 gal of water in the system.

With the engine running I reached down and grabbed the lower radiator hose at the water pump and can squeeze it flat and I feel no water being pumped out of the radiator. Thinking that maybe the radiator did not get enough water in it I pulled the upper radiator hose at the thermostat and poured water into the hose to fill the radiator. Within a couple of seconds I had water running out of the thermostat housing. So it looks like the radiator was full.

So, why is the water pump not pumping / picking up water?

The engine is still not running the best as timing goes but should not be a factor in this problem???

I have a Mech Temp gage I can install in the other head to compare with the car temp gage.

Or, I have a very big air bubble trapped in the system??

On a final note, should there be a spring in the lower hose? Mine does not have one and this is a brand new hose. It fits good but does flatten out a little in its present state.????

Sorry this is long, I welcome all tips and will post updates as I progress through this.

 

What happened between the test and the problem? Seems like the answer should present itself there. What was bumped, disassembled, unprotected from debris, etc.?

 

With the rad being cold like that, it sounds like there's little or no water circulation. You might have the dreaded air bubble syndrome. Lot of people here say to drilll 3 small holes in the outer part of the thermostat so a little water can flow when it's closed. Also, I wonder if your water pump is doing it's job. Is the belt tight? Can you see water running out of the fins in the radiator while it's runnin hot? With the engine warmed up and water circulating, the rad should not be cold.

Edit: Oh yeah, on the lower hose. I replaced mine a coupla months back and was told no spring was needed when I bought the lower hose. However, I took the spring out of the old hose and put it in the new one.

Brett

 

I have a 69 427 390 hp. My lower hose has a spring installed. I learned that upper radiator hose positioning is critical. Make sure the hose is not higher than the expansion tank. I read a thread by Larry B that was helpful. I also run a 160 stat. I had the wrong clutch for the fan at time of purchase, check the clutch for the radiator fan to see if the rotation arrow points in the correct direction. Mine was wrong.

 

Removed radiator form frame, installed body, installed radiator. Thats about it.

 

Reply is in blue above

 

see above in blue

 

Sounds like air pocket/bubble at the pump if it went hot that fast

 

Contrary to some opinions on the forum. Put a hotter thermostat in it, 160 is too low. You must hold the water back in the engine to allow the radiator to cool it. A 160 allows the coolant to circulate too fast for the radiator to recover. Dont consider since it`s a 427 that it automatically runs hot like some posts I have read. A statement like that is completely untrue. A stock 427 cooling system is more that adequate to handle almost any HP range. As simple as installing a hotter $5.00 stat will probably fix it as "EVERTHING" appears to be new.

 

Also stat might have stuck closed, take Ironcross' advise and switch it. $5 and an hour of your time.

 

A few years back a friend was building a '55 chevy with a 454. He had similar issues with high temps after his rebuild. After he changed all of the obvious things (rad, water pump, etc), he decided to pull the heads off. He found the problem: wrong head gaskets. I'm not sure if he had a Mark IV block with Gen V gaskets or the other way around.

After he installed the correct gaskets it runs cooler than my 355.

If you still have the paperwork on the motor rebuild, check the part #'s on the receipts.

 

I have to agree I would not put anything less than a 180 deg thermo on there. And also I would look into the corvettefaq.com site then go to cooling and look at the instructions for the fan clutch modifications that should be done. The fan clutches you purchase now do not come on till a higher temp unlike the ones that came with our cars. They modified them so they would be quieter and not come on so soon but it also can cause over heating as well. But if you follow those mods you can fix that.