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Discussion Starter #1 (Edited)
I am having an issue with my 1967 289 that I haven't been able to resolve.

Awhile back my car started to overheat when being driven on the freeway. Found I had a coolant leak due to a bad thermostat housing and did a flush and replaced the housing.

Car still was overheating after the flush. So I pulled the radiator out and took it in to have it dipped and flow tested. It came back as clogged due to deposits and etc in it. Since it was an original 2 core I swapped it out for a 3 core champion aluminium radiator.

I am still having issues with it running hot. Right before it had a loss of coolant I installed a Edlebrock intake and a Demon carburetor. Right now there is no thermostat in the car, I have good flow with the new radiator. Timing is set as best as I can due to not having a marker on the block. Engine runs great, idles well, drives great just gets hot quickly.

Could this be an issue with timing and or fuel ratio? Any other thoughts or ideas?
 

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Spammer Hammer
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195F thermostat. Drill a small hole 5/32" in the flange of the thermostat so that it is in the flow of the water. Install thermostat so the hole is at 12 o'clock position in the housing. Best of luck.
 

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Discussion Starter #4
195F thermostat. Drill a small hole 5/32" in the flange of the thermostat so that it is in the flow of the water. Install thermostat so the hole is at 12 o'clock position in the housing. Best of luck.
Never heard of drilling a hole into the thermostat? Is this to allow a little flow before it opens?
 

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Other possibilities:
-- Bad radiator cap (reduced pressure = lower boiling point)
-- Overfilled radiator with no overflow tank
-- Missing fan shroud
-- Bad temp sensor with stock temp gauge (how do you know it's overheating?)
-- Bad water pump (leaking thru weep hole is a symptom)
 

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Spammer Hammer
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Never heard of drilling a hole into the thermostat? Is this to allow a little flow before it opens?
Helps let air pockets out during the filling process. Also helps to jack the front of the car up to burp the system and make sure you remove all air. Trapped air turns to steam which can lead to overheating as well.
 

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Discussion Starter #8 (Edited)
Other possibilities:
-- Bad radiator cap (reduced pressure = lower boiling point)
-- Overfilled radiator with no overflow tank
-- Missing fan shroud
-- Bad temp sensor with stock temp gauge (how do you know it's overheating?)
-- Bad water pump (leaking thru weep hole is a symptom)
New Radiator Cap with the new radiator. I have another brand new one that i can try.

I don't have an overflow tank just the hose off the side of the radiator. Have an inch from the top of the tank.

Don't have a fan shroud. Don't think I could get one to fit around the new radiator. The old one didn't overheat till it got clogged. without the shroud.

New Temp Sensor but with the old unit it boiled over twice. New one I haven't let it get that hot as of yet. Just going off the gauge and praying it isn't a head gasket or something.

Replaced the water pump last year. No fluid leaks since I replaced the thermostat housing. I know I have good thermostat so I will put that in this evening.
 

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I have that problem too where the temp would rise to around 210-220 when I'm driving on some freeways, not all freeways but I don't drive freeways that much. I don't remember having this issue before I fixed the gap on the rear of my hood. It used to sit about 1-1 1/2" taller in the rear. Maybe that helped with cooling down the engine? Recently replaced the radiator but haven't really driven much on the freeway to know if the new radiator helped with the temp.
 

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I have that problem too where the temp would rise to around 210-220 when I'm driving on some freeways, not all freeways but I don't drive freeways that much. I don't remember having this issue before I fixed the gap on the rear of my hood. It used to sit about 1-1 1/2" taller in the rear. Maybe that helped with cooling down the engine? Recently replaced the radiator but haven't really driven much on the freeway to know if the new radiator helped with the temp.

Do you have the SS Spring in the lower radiator hose to prevent it from collapsing at highway speeds? That could be the issue.


Do you have a filter in the upper radiator hose to trap any particles the engine might throw so it does not get put into the radiator? I'm using a Tefba filter in the upper radiator hose. It has a SS screen, and once a year I drain out a bit of coolant, remove the top, take out the screen remove any debris and put it back in. Easy Peasy.
 

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Discussion Starter #11
Do you have the SS Spring in the lower radiator hose to prevent it from collapsing at highway speeds? That could be the issue.


Do you have a filter in the upper radiator hose to trap any particles the engine might throw so it does not get put into the radiator? I'm using a Tefba filter in the upper radiator hose. It has a SS screen, and once a year I drain out a bit of coolant, remove the top, take out the screen remove any debris and put it back in. Easy Peasy.
No spring in the lower hose. Wasn't one in there when I swapped out hoses with the new pump. Will get one on order for the piece of mind.

Also been looking at a filter. Just haven't pulled the trigger as of yet.
 

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+1 on the lower hose spring. Also check for a bad vacuum advance diaphragm or faulty DVCV (distributor vacuum control valve), if equipped. Yes, put the thermostat back in. It won't cure your overheating issue but it should be there to maintain a minimum operating temperature.
 

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Do you have the SS Spring in the lower radiator hose to prevent it from collapsing at highway speeds? That could be the issue.


Do you have a filter in the upper radiator hose to trap any particles the engine might throw so it does not get put into the radiator? I'm using a Tefba filter in the upper radiator hose. It has a SS screen, and once a year I drain out a bit of coolant, remove the top, take out the screen remove any debris and put it back in. Easy Peasy.
I have the spring in the old hose and the new one came with the spring also. Don't have a radiator filter. Don't think that's the cause of the heating on the freeway for me since temp is usually around 180 on the street. Did look into the Tefba filter but wasn't ready to spend the $70
 

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You do need a thermostat - they're there for a reason!

I also think it may be timing related. You really need to find a way to mark it so you can determine how much advance you're getting "all-in" (3000 rpm and above). It may be that you have too much advance or not enough advance at higher rpms, which would cause the car to overheat.

Have you verified that the carburetor is running right at higher speeds? If the car is running lean under heavier throttle, that could also contribute to higher engine temps. The Demon carburetors frequently need changes in jetting to really dial them in right, IIRC.

The last thing I would check is the intake installation. Are any cooling ports blocked off?
 

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I have the spring in the old hose and the new one came with the spring also. Don't have a radiator filter. Don't think that's the cause of the heating on the freeway for me since temp is usually around 180 on the street. Did look into the Tefba filter but wasn't ready to spend the $70

It is kind of pricey, but on the plus side you don't have to take the clamps off to clean the filter like many of the others. Mine used to overheat on the freeway also, but be OK around town. What I think is happening for you is that the radiator can't get the coolant cool enough and fast enough. Part of my problem is that I had a 4 speed and a 3:55 rear end so it would be at 3500 rpm at 70.


When I put in the 5-speed then at 70 the rpm is 1800. What also helped is when I put in the dual 11" 2800 CFM fans and that solved everything else. Now it will stay at 180 degrees even with the AC on, and stuck in over 100 degree temps getting out of Good Guys for over 1 hour.
 

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Discussion Starter #17
You do need a thermostat - they're there for a reason!

I also think it may be timing related. You really need to find a way to mark it so you can determine how much advance you're getting "all-in" (3000 rpm and above). It may be that you have too much advance or not enough advance at higher rpms, which would cause the car to overheat.

Have you verified that the carburetor is running right at higher speeds? If the car is running lean under heavier throttle, that could also contribute to higher engine temps. The Demon carburetors frequently need changes in jetting to really dial them in right, IIRC.

The last thing I would check is the intake installation. Are any cooling ports blocked off?
I have timing marks on the harmonic and they are clearly marked. The issue I have is what ever was attached to the block is missing. If I knew exactly where it was I could rig up something with a magnet to verify the timing. I have just gone off of a rough guess and till it runs smoothly.

I will reinstall the thermostat this evening when I go home. I pulled it to test to make sure it wasn't bad by making sure it opened when hot.

I installed the carb and haven't had a shop look over it. I leaned it out following the method of turning them in till it starts running rough and then back them off till it runs smooth again. When I installed the intake I made sure that it was all passages where clear. Though never know I could have made a mistake and worst case I will pull it off and do new gaskets and try again.
 

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Spammer Hammer
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One way to find the optimum timing is to drive around with the distributor just loose enough you can adjust. Drive up some large hills that will induce load on the engine. Adjust the timing up until you get pinging. When it pings, back it down just a degree or two or until the the pinging goes away under load. Tighten the bolt.
 

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I have timing marks on the harmonic and they are clearly marked. The issue I have is what ever was attached to the block is missing. If I knew exactly where it was I could rig up something with a magnet to verify the timing. I have just gone off of a rough guess and till it runs smoothly.
Do you happen to know how many degrees your distributor is advancing? That's the actual important part here. If you don't know what initial timing you're at and you don't know how much timing you're getting added in, it's easy to accidentally put in too much.

I know this because my car idles and accelerates best at 20* BTDC. But my distributor advances 26* to all-in. If I just set my car where it idles best, I would have 46* of advance by 3000 rpms, which is FAR too much (should be between 36 and 39 for most cars, I believe). I've done this before and the car did not do well at higher speeds :)

My suggestion for your issue would be to find top dead center first. Easiest way to accomplish this is to pull the #1 spark plug and put your thumb over the spark plug hole. Turn the engine over by hand until you feel air pushing at your thumb trying to escape the hole (this verifies you're on the compression stroke). Then, stick a screwdriver or something in the spark plug hole, and rotate the engine over until you feel the piston push the screwdriver out of the hole. When it stops pushing, make a note of where the balancer is at (magic marker and line it up with any discernible "landmark" on the engine). Then keep turning the engine over until you feel the piston start to move back down, which shouldn't be very much further on from there. Make another magic marker line using the same landmark as reference, and then split the difference between the two for true TDC. Rotate the engine backwards until it lines up with your true TDC mark. THEN, look for the 0*BTDC mark on your balancer - and that's where your timing pointer should go. After that, it's a simple matter of sticking a timing light on it to see where you're at for initial and all-in timing :)
 

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Discussion Starter #20
Do you happen to know how many degrees your distributor is advancing? That's the actual important part here. If you don't know what initial timing you're at and you don't know how much timing you're getting added in, it's easy to accidentally put in too much.

I know this because my car idles and accelerates best at 20* BTDC. But my distributor advances 26* to all-in. If I just set my car where it idles best, I would have 46* of advance by 3000 rpms, which is FAR too much (should be between 36 and 39 for most cars, I believe). I've done this before and the car did not do well at higher speeds :)

My suggestion for your issue would be to find top dead center first. Easiest way to accomplish this is to pull the #1 spark plug and put your thumb over the spark plug hole. Turn the engine over by hand until you feel air pushing at your thumb trying to escape the hole (this verifies you're on the compression stroke). Then, stick a screwdriver or something in the spark plug hole, and rotate the engine over until you feel the piston push the screwdriver out of the hole. When it stops pushing, make a note of where the balancer is at (magic marker and line it up with any discernible "landmark" on the engine). Then keep turning the engine over until you feel the piston start to move back down, which shouldn't be very much further on from there. Make another magic marker line using the same landmark as reference, and then split the difference between the two for true TDC. Rotate the engine backwards until it lines up with your true TDC mark. THEN, look for the 0*BTDC mark on your balancer - and that's where your timing pointer should go. After that, it's a simple matter of sticking a timing light on it to see where you're at for initial and all-in timing :)
That is easy enough. I basically did that when I pulled the distributor out and put it back in. Didn't mark the balancer but only takes a few minutes to spin the engine around to get the marks ready.

I am using a stock auto-lite distributor. I am figuring it is the C7OZ-12127-A. Any idea on the amount that a stock unit is advancing?
 
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