[Formulas]

Alan you plugged in the vacum can after setting initial and total.. but are you sure its working? .. did engine rpm change when you plugged it in ? did you verify by timing light? just plugging it in means an attempt was made to run vacum advance but thats no verification its working

[prostreet64]

I know you are being bombarded with a lot of info and questions but if you can would you post up a pic or 2 of the head gaskets?

[alanmay0]

my total timing is 31 plus vacuum advance. I cant tell you what that is now because the heads are off of the engine trying to figure out why it is running hot. I agree the cooling system is very simple and i should not be having this problem but i do and it seems no one has yet given me a suggestion that has proven to help me. I would guess that my vacuum advance adds about 12 14 degrees making my total total advance at about 2800 rpm 43 46 degrees. This may be to low or to high don't know just know that my engine temp slowly rises from normal non running temp to 240 degrees in about 7 miles at 65 mph w/o the ac on. I'm sure the problem is something simple but so far have not found it. so on this board ask me questions only an engineer would know the answers to and then get mad that i cant provide it. what is a "cavernous piston quench", and "compromised cooling pressure". that sound interesting not heard of it before. I have checked and rechecked the water pump myself and all is as it should be. Have the kooler something water pump suppose to be the best for the Pontiac. I am gonna try again the 7 blade clutch fan with the factory shroud. I have just ran out of things to try. took heads off yesterday hoping to find a bad gasket but nope all was good. now have to but it back together.

[alanmay0]

yes the rpm change when i attach the vacuum hose to the vacuum advance pod. Also verified by timing light but cant give you the degrees because i did not make a not of it. thanks

[alanmay0]

here are pictures of the gaskets both sides. thanks

[johnta1]

To me, the radiator can not cool if it is not getting outside air. (from in front of the car)

If your ac condenser is in front of the radiator, it is blocking all the flow that should be going to the radiator.

If the shroud is not there that is a definite loss of cooling.

A mechanical fan is lots better than an electric fan if not set up correctly.

A radiator cap that is not pressurizing correctly will also cause overheating.

All of these adds up to overheating in my book?

[promptcritical]

Maybe be sure if the tune first. Timing in particular. Full advance and at what RPM and then vacuum advance all in. Add them together…you know that. Your radiator seems to work…you have a decent delta-T from the inlet to the outlet. Seems the water is coming into the radiator too hot…goes back to the tune or those pistons??

[tom s]

Where in TX are you?We have some very smart board members in TX that might be able to help!Tom

[alanmay0]

all sounds good except all ac cars have the condenser in front of the radiator that is the way they are made, new and old cars.

[alanmay0]

im in south fort worth

[Gator67]

About 10 years ago I had the 400 in my 67 rebuilt (stroked to 462) and temps would creep-up for no apparent reason. After a couple months we had to pull the motor to fix a rear main leak and at the same time we advanced the cam slightly (I think Ken Keefer suggested this to us). It solved the problem. Not sure why, but the car has run cool ever since.

[25stevem]

In responce to the above post the reason is due to the Cam timing change producing the needed cylinder pressure at the right time to pump out the Exh gasses effectively.

To me and as has been posted in reply as part of this string many times, I think the OPs problem is two fold, not enough cylinder pressure in combination with not enough timing , at least in terms of driving down the road at more then 30 mph.

His engine running hot at idle is all about air flow

[400 Lemans]

Definitely pull the timing cover and check the cam timing. Depending on which timing gear set was used it could very well be out of time. Sometimes the 3 keyway sets can get confusing to some, with a lot of different symbols to go by. But you have been through everything else and it all starting to point to this now. My guess is its set to retarded.

[Cliff R]

IF and WHEN you determine that the problem isn't directly related to nor can it be solved by the cooling system, or the tune, go back and read what I've put up here on those pistons, and cam timing.

I've cured several 400 engines over the years with the EXACT same pistons you are using.

Never saw the cam specs or where it was installed but you can improved things in that area as well.

With tight quench, less quench area, and pistons not WAY down in the holes at TDC that alone will knock 20-30 running temps right out of it with no other changes.

I moved the cam in one 400 we had in here that climbed right past 200, then 220, 230 degrees etc really quickly after start-up and after the cam was retarded 4 degrees we had trouble getting it up to temp. The "builder" on that one simply advanced the cam with one of those POS 3 keyway cheap double roller chains and because he believed that it would make "more low end torque" and allow for "chain stretch". Both of those myths will very quickly get you into trouble with these things.......FWIW.......

[Schurkey]

Originally Posted by Cliff R

I moved the cam in one 400 we had in here that climbed right past 200, then 220, 230 degrees etc really quickly after start-up and after the cam was retarded 4 degrees we had trouble getting it up to temp.

I'm just surprised to find that retarding the cam (and only 4 degrees) made such a positive improvement.

[25stevem]

I must admit that I am also!
Was it ever determined exactly how far off that cam gear was, and if the cam was maybe off also?

[tekuhn]

Originally Posted by JLMounce

Here’s something to temporarily try. Plug the back of the head where it would typically exit to the heater core. Then, plug the heater core return on the water pump.

Part of what could be happening is that the circulation of hot water heads back to the water pump, then to the engine and bypasses the radiator.

I’m not an expert on this but it’s my understanding that there is supposed to be a check valve to restrict water flow through the heater core on AC cars, except when the heater is on.

If closing off the heater core loop helps, that may help to pinpoint where the issues are........

This is an excellent suggestion. The nipple that goes in the head is supposed to have a restrictor in it to limit the flow through the heater core. If that is missing or is an incorrect aftermarket piece, it might be allowing too much coolant to bypass the radiator. JLMounce is also correct about the direction of flow. Hot water leaves the head going to the heater core, and then is returned to the water pump inlet. This coolant bypasses the radiator, and unless your heater is on, has had no heat removed from it.

Another place where hot coolant is allowed to flow back to the pump inlet and bypass the radiator, is through the hole at the back of the timing cover that is sealed to the intake manifold water crossover with the rubber washer and long bolt. If that hole has corroded and increased in diameter significantly, it might be allowing too much coolant to bypass the radiator.

Both of these potential problems seem unlikely, but if you're dealing with several smaller issues that have snow-balled into one big problem, it could be adding to the problem.

My personal preference is always an engine driven fan. Use a factory A/C fan, full shroud, and heavy-duty thermostatic fan clutch and also ensure all the factory rubber seal pieces are present which prevent air from going around the radiator. The fan blades should be centered front to rear (half in and half out) in the shroud opening to ensure proper fan function.

[tom s]

Just by pass the heater for awhile to rule out one thing!Baby steps,one thing at a time.JMHO,Tom

[Sirrotica]

As has already been said, very few electric fans will move the amount of air required to cool a Pontiac Stratostreak. Having run them on a dirt track it is paramount to move enough air to keep them cool. I used a 6 blade composite RV fan with almost a 90 degree pitch. I've used the same fan on street driven 455 T/As, works very well

Pontiac engineers knew this and that is the reason they used pulleys to speed up the water pump, and fan speed, 4 core radiators, and large fans with a lot of pitch on the blades. Speeding up the water pump also creates more pressure in the block, minimizing the possibility of steam pockets forming. the engineering is already done, the fixes do work.

If you're intent on changing the engineering that is already proven, you're setting yourself up for problems. Those problems show up frequently on these boards.

One thing some don't take into account is how large of a iron heat sink a Pontiac is. There is a lot of mass there and when it gets hot, it takes much more removal of BTU than an LS, or even a SBC does to reject the heat. A cooling system for any large engine is much more robust than a smaller lighter engine is. look at the difference it takes to keep a BBC cool, compared too a SBC. A 2 core brass radiator will cool a SBC, but put a BBC in the same car, no way it will work with a 2 core radiator.

Over the years I've worked on a lot of different brands of cars with vastly different engines. I've paid attention to the radiator and fan requirements that the factory has used to keep them cool. Pontiac has always had some of the most robust cooling systems of all brands. There is a reason for that.

When you start deviating from what the factory engineers did, is when you start running into overheat situations. These cars when new sold in the sunbelt states, with A/C, and they worked just fine until someone either neglected them, or started tinkering with what THEY though should cool better.

My parents lived in Phoenix since 1980, they owned nothing but Pontiacs with A/C, no overheat problems that I ever knew of, and I would be the first one my dad would have spoken to if he was having any OH problems.

[alanmay0]

Well I think i have fixed the over heating problem in my 67 GTO. I changed the head gaskets, put in new iron impeller water pump. different aluminum radiator with 7 blade heavy duty clutch. So have only driven it one time and the temp outside was cool, around 65 degrees and all was well so i will see tomorrow when it will be in the 90's. Now I have a different problem which i need help with. Since making all of the changes for the over heating i now have a situation when i first start the car. It sounds like it is trying to clear it throat, if you know what I mean. It sounds like it is not running on all 8 cylinders when it first starts and it take it about 5 to 10 seconds of me revving it up to clear out whatever is in the cylinders. I have done a compression check and all it well 145 150. I have removed all of the plugs and they all look ok. So I can't figure out what is causing the misfiring, popping sound that seems like a cylinder or two have to get cleared out before the engine runs smooth. Any and all suggestions appreciated.
thanks
alan