Pontiac 400 Overheating Concerns - Pontiac GTO Forum
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post #1 of 33 (permalink) Old 09-23-2019, 02:38 PM Thread Starter
 
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Pontiac 400 Overheating Concerns

Hello good Pontiac people. Last year you helped me out while I was working on a guy's '67 GTO with the 400 and auto transmission. That one is finished and returned to the owner.

A couple of months ago I took on a project to complete the build of a friend's '67 Firebird with the Pontiac 400 and a 700R4 transmission. One problem he has is it quickly overheats. Reading about this it seems the big cube Pontiac engines often have this problem.

Anyway, I have rebuilt the suspension with new springs front and rear, installed the side glass and door panels and the remainder of the interior. Now I've turned my attention to tuning and the over heating.

This an engine he had built by a local builder who has (had, since he is now deceased) a good reputation. It looks nice under the hood, but the owner has no specs of the internal components. The shop tells me they purge their records after 2 years so I really don't know what's in it.. The engine seems to be mostly stock, or maybe a mild cam, based on observing it running.

I found the timing too advanced and set it to 34 BTDC at 3,000 & greater. I found the distributor clamp bolt was bottoming out before the clamp secured the distributor. That has been corrected. The engine pulls about 17in vacuum at idle and the vacuum advance is all in at 14in. I moved the vacuum advance connection from the Port vacuum to Manifold vacuum on carb. He has an Edelbrock carb that I've set the air-fuel mixture screws using the vacuum gauge. He has a factory fan shroud on a 4-row aluminum radiator with a 5 blade flex fan. The flex fan has 3/8" diameter clearance on one side and nearly 2" clearance on the opposite side. It was sitting really deep inside the shroud so I replaced the 2" fan spacer with a 1" spacer. Anything thinner and the fan blades hit the power steering pump pulley bolt.

With the tuning it runs hot but less aggressively than before. My most recent improvement was to install a FlowKooler hi-Flow water pump. https://www.summitracing.com/parts/bra-1649 This car has no heater core but had the hose connecting the rear passenger head to the timing chain cover. My thinking was this circulates hot coolant through the system without filtering through the radiator, so this morning I removed the jumper hose and plugged both ends.

I topped off the coolant after first filling it though the opened thermostat location, replaced the thermostat, and let the engine run with the radiator cap off to burp the engine. When the temp gauge reached about 175 the engine began to vibrate and coolant sloshed out the radiator. I turned off the engine and let things cool off again. After I topped off the radiator I ran it again with the 16 lb radiator cap back on. It seems when the thermostat opens there is a vibration that sounds like it is from the water pump or thermostat. Does the heater core hose provide a sort of relieve valve that allows some circulation even when the thermostat is closed? Should I put the jumper hose back? Or is this air in the system that is somehow hammering when the thermostat opens? Even though I spilled some coolant when draining and changing the water pump it didn't require any additional to top it off.

I've invested a lot of time on this engine and want to get it under control. I know this isn't a GTO but I hope you guys will still assist. I'll be glad to answer any specific questions. I am stumped.

Update: I topped off the coolant, raising the radiator coolant level a couple inches, replaced the cap and tested it again. It started the rattle again at 157 degrees and then it reoccurred with no apparent relation to the thermostat opening. It got to 192 degrees then settled back down to about 186. The cooling concern seems better but now the rattle. It reminds me of water hammer in an older house when you turn off the water and it hammers inside the wall. Is this related to the heater hose bypass shut off?

Last edited by Andrew69; 09-23-2019 at 03:37 PM.
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post #2 of 33 (permalink) Old 09-23-2019, 08:11 PM
 
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If you keep filing the radiator and top it off each time before starting, it will push anti-freeze out each and every time and you will be doing that to eternity.

Does the top of a radiator has an expansion tank? Or is it a crossflow with the tanks on the side (which I think they had)? Water expands when hot. The level will be down about 1 1/2 or so on a radiator with a top expansion tank each time you look at it after it cools. As long as you see some water above the core tubes, you are good. The water level will find its own level. Same goes with the side tanks, let the water find its level and then check - you should be able to look in and see it not too far down on the side.

I would also suggest a laser temp gun to verify the engine/radiator running hot. It may not be.

As to the noise, never heard of that one before. May be a problem with the FlowKooler installation - something expands when hot and is now hitting/wrapping on something.
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post #3 of 33 (permalink) Old 09-24-2019, 07:29 AM
 
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Sorry if I missed it, but what kind of radiator are you using and what thermostat? As far as fans go, I did not have great luck with the flex fans. My car runs significantly cooler with a large aluminum radiator , stock water pump and 180* thermostat, and stock fan (with crappy shroud). I drive the car hard in 90*+ weather and never see anything more than ~190-200. Obviously it gets hotter when I park the car.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #4 of 33 (permalink) Old 09-24-2019, 12:09 PM Thread Starter
 
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It is an aluminum 4 row radiator with a 180 degree thermostat that was tested in a pan on the stovetop. I was successful in capturing this rattle on video and loaded it to YouTube. This rattle may or may not be related to the overheating concerns. It is a recently occurring concern.

This morning I replaced the heater core bypass hose and with the thermostat removed I filled the radiator with coolant until the thermostat cavity was full. I installed the thermostat and then topped the coolant to several inches below the cap.

I started the car and backed it out onto the 5 degree incline leading to the garage. I know someone said no angle is needed, but if it pukes out I would just as well it be outside where I can easily wash it away.

There I let it idle for 20 minutes while I observed the fluid flowing in the radiator and the car gradually heating. It never puked out and was flowing pretty well. The heat seemed to be in control but then gradually went to 203 degrees before I shut it down.

The intermitted chatter continued with no obvious pattern related to thermostat opening or oil pressure dropping. The oil pressure remained between 56 and 65 depending on my revving the throttle or resting idle. This video captures the noise between the 11 second and 29 second span. If this won't play go to YouTube and search for Pontiac 400 Rattles to see the video directly.


Last edited by Andrew69; 09-24-2019 at 12:24 PM.
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post #5 of 33 (permalink) Old 09-24-2019, 12:25 PM
 
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looks like a blade is ready to break on the fan

that fan doesnt look original... I dont think our pontiacs ever used a 1" spacer...
leads me to believe its the wrong fan ...

is it bent or out of balance .... ???

was the water pump divider plate clearanced ??

Scott
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post #6 of 33 (permalink) Old 09-24-2019, 12:52 PM Thread Starter
 
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It’s an aftermarket 5-blade flex fan with a 1” spacer to set the distance from the power steering pump. If it were replaced what would be preferred? I didn't build this engine or select the components. I am working to overcome the overheating concerns.

The water pump divider plate was clearances to ~ 0.060 space. Removing it to see if there is interface isn’t a quick job. The noise seems to be coming from the body of the engine and the driver’s side. Best that I can tell.

What about that rattle? Is it related to air in the block or a more serious problem with the engine?
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post #7 of 33 (permalink) Old 09-24-2019, 01:14 PM
 
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ok....
it looks like a reproduction of the factory flex fan ,,, thats a good one ...

have you fired it up with NO belts and reved it up ?

hmmmmm

real nice n tidy engine bay ...

could it be the alternator ,,,, like some one forgot the spacer behind the cooling fan

it looks like it needs a correct 69 front alternator strap ,,

sometimes we go to ac pulleys .. large on the bottom smaller water pump ,,, seems to help low rpm cooling,,,

....

hmmmmmmm

gotta get back to work
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post #8 of 33 (permalink) Old 09-24-2019, 05:35 PM
 
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Because it kicked on and then kicked off, I am going to say it is the alternator when the charging cycle kicks in.
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post #9 of 33 (permalink) Old 09-24-2019, 10:03 PM
 
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Sounds like the fan hitting the shroud, or touching a belt. Also make sure the fan mounting bolts are not or have not worked loose, that will give a knock like that. I would examine all around the shroud and the belts and see if the fan is flexing out and barely striking something, look on the bottom of the shroud good. The shroud sits in a little groove at the radiator bottom and if not set in right could ride high.

You can remove belts one at a time to try to isolate the noise, likewise you could remove the shroud, try it for a minute, remove the fan try it for a minute, remove a belt etc. if the noise is eliminated you can investigate further.

It looks like your fan is out the back of the shroud, but hard to tell. Anyway it should be half in and half out for proper cooling, too far in or out of the shroud will make it run hot....

Stay with it you will get it, I would eliminate the moving parts, fan, belts, pulleys first.....if the sound is not there, put your stethoscope or rubber hose to the valve covers and engine....rockers, pushrods etc....but on the video, sounds like it is up front.....
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post #10 of 33 (permalink) Old 09-25-2019, 09:44 PM
 
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Originally Posted by Lemans guy View Post
Sounds like the fan hitting the shroud, or touching a belt. Also make sure the fan mounting bolts are not or have not worked loose, that will give a knock like that. I would examine all around the shroud and the belts and see if the fan is flexing out and barely striking something, look on the bottom of the shroud good. The shroud sits in a little groove at the radiator bottom and if not set in right could ride high.

You can remove belts one at a time to try to isolate the noise, likewise you could remove the shroud, try it for a minute, remove the fan try it for a minute, remove a belt etc. if the noise is eliminated you can investigate further.

It looks like your fan is out the back of the shroud, but hard to tell. Anyway it should be half in and half out for proper cooling, too far in or out of the shroud will make it run hot....

Stay with it you will get it, I would eliminate the moving parts, fan, belts, pulleys first.....if the sound is not there, put your stethoscope or rubber hose to the valve covers and engine....rockers, pushrods etc....but on the video, sounds like it is up front.....
Sounds like the fan hitting the shroud to me .
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