I have a 69 with a bespoke 454. I had cooling problems so I recently fitted a bespoke new aluminium radiator. Now the water does not boil of as steam but gushes as water out of the Header Tank at certain tempratures. I am in the UK.

The engine is a high performance block from a boat, rebored with high compression pistons for 9.5:1 compression. Edelbrock Performer hydraulic camshaft. Edelbrock Performer Intake Manifold. Holley 750cfm Vacuum Secondaries Carb. Hood Scoop for cold air induction. Hooker Headers and Big Block side pipes. The engine was designed to put out at least 450 bhp at the wheels. So it almost certainly is generating a lot of heat and has a non standard water cooling circuit.

The radiator is a maximum efficiency aluminium new radiator specifically made to fit. It undoubtedly has more water in it than a stock radiator.

After the new radiator was fitted I noticed that the engine was fine for a while then I saw steam and the temprature would rapidly go up. This happened several times. My original stock header tank was aluminium so I could not see what water level there was. Water would gush and then hit my exhaust creating steam. This broke my old header tank creating cracks.

I took the car back to the mechanic who fitted the Radiator. He did tests on the coolant and found no trace of exhaust gasses so not a blown head gasket. He fitted a new clear plastic header tank and bled the air from the coolant. Otherwise he could find nothing wrong.

I took the car out for a test drive and drove it around for a couple of hours with a whole mixture of conditions from heavy traffic to several blasts at full throttle. The temprature stayed at about 180 degrees. Then when I was parking the car it happened again. The clear plastic header tank was completely full with no air and water was gushing out of the cap hitting the exhaust hence creating steam. After it had cooled down the header tank was completely empty. I put 2 or 3 litres of water back into the system before the water level was a good 3 inches below the cap.

My theory is that by fitting a bespoke engine and bespoke radiator I have considerably more coolant than I had before and now have exceeded the capacity of the Header Tank to contain the water expansion even if it is completely empty when cold. So when the temp reaches say 185 it blows the cap and starts gushing out. This creates a syphon effect and the cooling system is no longer cooling the engine effectively which then rapidly overheats.

Has anybody else experienced this problem ? Can anybody recommend a solution ? Obviously fitting a bigger header tank might work any ideas ?

 

Are you sure that all the air was bled from the cooling system? Is the lower radiator hose collapsing. I have seen this before, and it is usually caused by the coolant level being to low.
What seems to be happening from your explanation, is that as long as the engine is running and coolant is circulating through the system you don't have an overheating problem. When you shut it down, and the coolant is no longer circulating you get a boil over.
I would suspect that you have air trapped in the system which is allowing the coolant to boil.

Just a suggestion.

 

Can you tell us whether the header tanks that were/are fitted are the pressurized or non-pressurized variety?

 

You could even have the wrong type of radiator cap. If you have a cap made for a non-return system, it won't return coolant from the reservoir, causing the radiator to build up steam and causing more fluid into the reservoir and out it's relief tube.

When you park a car and shut the engine down, the temp actually rises for a while as it's no longer circulating and getting cooled...that's normal. If it's steaming as you say, then it sounds like there's simply not enough coolant to keep the engine at normal temps after shutdown. As it gets too hot it turns to steam and goes out the overflow and isn't coming back...that's why it sound like the wrong type of radiator cap...or a bad cap.

 

I would confirm you have the correct radiator cap and that it works properly.

Are you running proper coolant mixture? (You don't want dissimiliar coolants mixed)

I also agree that you may still have an air lock in the system. What has almost always worked for me is to run the engine with the heater turned to full hot to ensure full coolant movement.

Also, I believe that 180 degrees is a bit light for your engine, you should be running with 195 thermostat.

 

Many thanks for all your replies.

My original stock Header Tank was pressurised with the correct cap. This cracked and was replaced with a clear plastic Header Tank which is also pressurised as an experiment to see what is actually happening. This was not a Corvette header tank just a UK model car header tank of the shelf as I am so far of the rails from stock, what does it matter ?

I took the car to a carshow today and I was asked to parade round the arena, which meant spending about 15 minutes at very slow speed if not idling. The engine was getting a bit warm so I switched it of several times in an attempt to cool it down. I eventually dived out of the arena back to my parking space and switched the engine of as it was gushing again.

A spectator said that there was a blast of hot air from the front of the car which made him feel that my auxiliary electric fan was blowing the wrong way. I forgot to mention that. I had one fitted to compensate for the slow idling speed of the engine and engine driven fan. I have the original stock fan and an electric auxiliary fan. Obviously if true then this does not help and I will investigate.

However what astounded me is that when gushing my Header Tank was completely full of water. After the electric fan cut of (it is thermostatically controlled) I sat and watched it and after 10 minutes the Header Tank was completely empty of water as it cooled. I put another 1.5 litres of water in to be about 1 inches above the bottom of the tank leaving 3 inches of clear air.

I suspect that there is no single problem which is why my mechanic has not figured it out and fixed it. If the electric auxiliary fan is blowing the wrong way then that is very bad but only has an effect when it cuts in.

Due to the fact of this cycle of Header Tank gushing and then being completely empty I could well have some air pockets in the system now, however when the car left my mechanic he had gone to extreme methods to bleed every last bit of air from the cooling system. He did end up putting an additional 2 litres of water back in the coolant.

In short it is not the correct coolant mixture as it keeps gushing and is replaced with water.

What puzzles me is that the water does not boil of, it gushes as water.

 

This system was never designed to be devoid of all air. Because of the low and slanted radiator mounting, GM utilized an expansion system as a means of compensating for a fill point that would have been lower than the motor if the standard filler point on the radiator were used.

The way this system works is when the engine is running, all the air collects in the expansion tank so the motor and radiator can be completely filled. When the engine has been shut off coolant will want to seek it's own level and will rise in the tank through it's lower hose, the air in the tank will be pushed up into the intake and heads as the liquid levels out. It sounds like it's got intestinal problems when this is happening.

BB A/C cars had a larger tanks than the non A/C cars to provide more volume for expansion. Check to be sure your tank is big enough.

I'm thinking your engine temp creep is another problem like a defective/wrong fan clutch. For some reason you aren't getting enough air flow across the radiator at idle.

 

After I got my new high performance engine installed I had two over heating problems. Firstly when idling it over heated after about 20 minutes, secondly if I sustained a speed of 75 plus mph for more than 15 mins then it over heated.

The fan and water pump were stock, driven of the engine so I guessed that the idling speed of he engine was too low to effectively drive the cooling system at idle. I fixed this by having an electric auxiliary fan fitted which was thermostatically controlled. This problem was then solved.

However that did not fix the other problem at high speed. I have a 3 speed TH350 gearbox which means high revs at speed and lots of heat. So when my rad started to leak I thought it was time to try and fix this problem once and for all. So I commisioned a purpose built new aluminium maximum efficiency rad specifically built for my car. In the process I discovered I did not have an original stock rad but a cut down version smaller than usual which was ridiculous for a high performing big block. My new radiator was built by the leading radiator manufacturer in the UK.

After the new rad was fitted I had the return of the overheating at idle problem but possibly seemed to be ok at speed. In the process of fitting the new rad the electric fan was moved from the front of the rad to the back of the rad, unless the blade was reversed this is not going to work. I trust my mechanic and am astounded they might have made such an obvious mistake (but it is worth checking). Also the engine driven fan was removed and then refitted (maybe it was not entirely refitted correctly).

The overheating broke my orginal stock header tank producing cracks, but I guess it was old and prone to failure at the least sign of pressure. I have a new clear plastic header tank now which I can clearly see what the coolant is doing. I am astounded that the tank can be completely full, bursting, as it gushes water and then completely empty 10 mins later as it cools.

I think I have a combination of problems which is why it has not been fixed easily.

Firstly I need to get the auxiliary electric fan checked to make sure it is blowing the right way, but that only has an impact when it kicks in.

Secondly I need to check that the engine driven fan was re-installed correctly with all the clutches in good working order.

Finaly is my Header Tank big enough ? Perhaps a bigger tank would be better.

So can any of you point out what I should look out for with the engine driven fan, i.e.; what clutches there are and how to check them out.

Secondly can anybody give an idea of how big a header tank I might need and a possible, of the shelf, tank that might do the job.

Many Thanks for any help