Iratic temperature swing - overheating

[Joe P.]

First some background...

What has been done...

new thermostat last year,
new proper temperature sending unit from Lectric,
new hoses, 2 years ago,
new aluminum DeWitt rad, just installed,
new heater core just installed,
new clutch fan last year,
water pump rebuilt last year,
new pulleys,
Fan belt is tight,
new seals added to bottow of rad support
harmonic balancer spacer was installed,
cooling system flush and reverse flush,
new prestone 50/50 mix,


Just finished installing the new rad, new pulleys, heater core, shroud, started up after a few pumps, seems to be running a little rough. Not bad, since it hasnt been started since October.

I put in the first container of mixed 50/50 prestone and thats all it took.. found this odd.. i let the engine heat up and couldnt get any more in.. i drove around the block and the temperature gauge shot up to 220.. When i got back to the drive way, i popped the hood and saw fluid everywhere. I let it cool down removed the cap and then added another container of mixed antifreeze.. off again and the same thing happened... i ended up going to a 13 pound rad cap, and off again this time the temperature shot up to 210 and the fluid came out the overflow hose.. at least i didnt have to clean the engine compartment a fourth time.


What i dont understand is why with the new aluminum DeWit rad and a new heater core I am running so hot? From all the posts the new rad should be running cooler than the original brass rad that i replaced. Within 5 minutes of driving the temperature gauge goes from 100 to 220.. At one point it dropped in idle from 220 to 180, but when driving it is between 210 and 220..

I took a IR gun and checked the temperature of the thermostat housing and they seem to be measaureing accuratlly.. 220 on the gauge is 220 on the gun.


I have the proper CS solid lifter block, with a 64 exhaust manifold (3844457) in place of the FI unit, and running with a 62 tach drive distributor (1110985) without a vacumn control and electronic ignition.

I think at this point i either have a sticking thermostat even though its a year old, or the timing needs to be reset..... i am stumped..

So i am looking for some advice on setting the timing with this combination, and any suggestions why i am overheating..

The pics below show the alignment of the fan to the shroud..

[Dick W.]

Re: Iratic temperature swing - overheating

First some background...

What has been done...

new thermostat last year,
new proper temperature sending unit from Lectric,
new hoses, 2 years ago,
new aluminum DeWitt rad, just installed,
new heater core just installed,
new clutch fan last year,
new pulleys,
Fan belt is tight,
new seals added to bottow of rad support
harmonic balancer spacer was installed,
cooling system flush and reverse flush,
new prestone 50/50 mix,


Just finished installing the new rad, new pulleys, heater core, shroud, started up after a few pumps, seems to be running a little rough. Not bad, since it hasnt been started since October.

I put in the first container of mixed 50/50 prestone and thats all it took.. found this odd.. i let the engine heat up and couldnt get any more in.. i drove around the block and the temperature gauge shot up to 220.. When i got back to the drive way, i popped the hood and saw fluid everywhere. I let it cool down removed the cap and then added another container of mixed antifreeze.. off again and the same thing happened... i ended up going to a 13 pound rad cap, and off again this time the temperature shot up to 210 and the fluid came out the overflow hose.. at least i didnt have to clean the engine compartment a fourth time.


What i dont understand is why with the new aluminum DeWit rad and a new heater core I am running so hot? From all the posts the new rad should be running cooler than the original brass rad that i replaced. Within 5 minutes of driving the temperature gauge goes from 100 to 220.. At one point it dropped in idle from 220 to 180, but when driving it is between 210 and 220..

I took a IR gun and checked the temperature of the thermostat housing and they seem to be measaureing accuratlly.. 220 on the gauge is 220 on the gun.


I have the proper CS solid lifter block, with a 64 exhaust manifold (3844457) in place of the FI unit, and running with a 62 tach drive distributor (1110985) without a vacumn control and electronic ignition.

I think at this point i either have a sticking thermostat even though its a year old, or the timing needs to be reset..... i am stumped..

So i am looking for some advice on setting the timing with this combination, and any suggestions why i am overheating..

The pics below show the alignment of the fan to the shroud..

If all the coolant you put in was that one container, you are quite a bit low of coolant.

[Rich P.]

Re: Iratic temperature swing - overheating

Dicks correct, you probably have an air bubble. You need to jack the front of the car up, remove the thermostat and housing then fill the motor through the thermostat opening. As you fill the motor up sometimes you can hear the motor gurgaling as the air moves out. This is not always necessary but I have had to do it once or twice. You can actually feel the hot and cool spots move from the motor to the radiator when there is a bubble in the system.

Rich

[Joe P.]

Re: Iratic temperature swing - overheating

If all the coolant you put in was that one container, you are quite a bit low of coolant.

Dick that was the first time around the block... on the next two drives around, i kept filling up the rad... If i have a bubble in the block and drive up a ramp with the engine running above 180 degrees, will the bubble move into the rad?

[Joe P.]

Re: Iratic temperature swing - overheating

Dicks correct, you probably have an air bubble. You need to jack the front of the car up, remove the thermostat and housing then fill the motor through the thermostat opening. As you fill the motor up sometimes you can hear the motor gurgaling as the air moves out. This is not always necessary but I have had to do it once or twice. You can actually feel the hot and cool spots move from the motor to the radiator when there is a bubble in the system.

Rich

Ok,, i will try it.. How high do i have to lift the front end, so the thermostat housting is the high point.. Do i have to drein the rad.. so if i start taking the thermostat housing off and fluid comes out,, iand fluid comes out then would this mean the air pocket is gone?

[Dick W.]

Re: Iratic temperature swing - overheating

To prevent BS like this, I have started drilling a .125 hole in the thermostat. It will self bleed the air out that way. In almost 50 years of fooling with these old cars, I have had that happen 2-3 times, but the agravation can justify a few minutes drilling that hole.

[Wayne P.]

Re: Iratic temperature swing - overheating

Dick. you mentioned drilling a vent hole in the thermostat 1/8 . do you drill it on the flang that sits on the intake ? Thanks

[Joe P.]

Re: Iratic temperature swing - overheating

I hope its the flange..

I put the car up on ramps, and pulled the thermostat housing and thermostat off the car,

Put that thermostat and another into my wifes favorite pot and watched the GM 180 thermostat start opening at 180, Let it cool and drilled a 1/8" (.125") hole into the flange. The Rad fluid was coming out of the manifold, so i drained some fluid from the rad, then topped up the mainifole, replaced the thermostat with a new gasket, topped up the rad, and went for a drive..

Things were looking up, and the temperature starting to rise, and got up to 220.. and back down to 170 and then was between 180 and 220..

So I am going to check the timing.. I actually took the cap off and found that i have a double point distributor, it had not been converted to electronic like i thought previously.

I also am going to run a seperate temperature gauge to compare results. I tried with an IR gun, but the swings are so fast sometimes that its not very accurate to compare.

I am also going to order a new wire conecting the temperature sending unit to the gauge.

[Duke W.]

Re: Iratic temperature swing - overheating

I'm not sure what you've got, but it sounds like a 290 HP FI engine, but the FI has been replaced with a manifold and single four-barrel.

Too little total idle timing is a sure way to overheat during extended idle periods.

A Duntov cam engine needs about 30 degrees total idle timing to achieve lowest idle EGT and minimum idle fuel consumption, and the only way to achieve this is with a vacuum advance distributor, which you don't have, but I recommend you get one and set it up to '65 SHP/FI specs.

In the meantime advance the initial timing to as high as possible without detonation. This might be even off the tab, so limiit it to about 18 on the tab.

If you don't pull the block drains, the block will retain 6-8 quarts and you will only be able to add about half the approximate 16 quart refill amount.

The block should always be drained with every coolant change.

Coolant should be added slowly and the car bounced up and down after every 2-4 quarts. Once full start the engine and monitor the level. When the thermostat opens the level will drop, so add as required to bring to the full level, then install the cap and drive the car around the block a couple of times. Let it cool for awhile and check the level again. Also check and correct the level for the next couple of heat cycles until it stabilizes at the OE recommended level specified in the owners and service manuals.

Duke

[Joe C.]

Re: Iratic temperature swing - overheating

Drain the complete system...........especially and including the block, by removing both drain plugs. Run some coat hanger wire into both drain holes to be sure to clear all of the cr*p out of the lower block (a dirty/plugged lower engine block water jacket will NOT cause your problem, what it WILL do is cause a rise in your oil temp.).

Look for the coolant capacity in your owners manual. Take note of how much fluid a dry fill takes, and you'll know, for sure, what you've got.

The thermostatic fan clutch should be fully engaged after your road test, and it should be "roaring" when you gun the engine.

I have never seen a system air bound to the extent that it would prevent (about) 1/2 gallon of coolant from entering the system (assuming your engine block is already full)!

Is the engine still running "rough"? Do you have a "miss"? Timing could be a bit retarded, but hard to believe that it would boil over so quickly unless there is GROSS misadjustment.
Is your valve lash set properly?
Are your head gaskets intact?
Could be a lot of things.

A sure fire check for exhaust leaks into the cooling system is to remove the thermostat, remove the fan belt, fill the engine to the thermostat flange in the intake manifold and run the engine briefly while looking for bubbles in the thermostat opening.

[Jack H.]

Re: Iratic temperature swing - overheating

It should 'burp' itself free within a reasonably short run time...

[Joe P.]

Re: Iratic temperature swing - overheating

I'm not sure what you've got, but it sounds like a 290 HP FI engine, but the FI has been replaced with a manifold and single four-barrel.

Too little total idle timing is a sure way to overheat during extended idle periods.

A Duntov cam engine needs about 30 degrees total idle timing to achieve lowest idle EGT and minimum idle fuel consumption, and the only way to achieve this is with a vacuum advance distributor, which you don't have, but I recommend you get one and set it up to '65 SHP/FI specs.

In the meantime advance the initial timing to as high as possible without detonation. This might be even off the tab, so limiit it to about 18 on the tab.

If you don't pull the block drains, the block will retain 6-8 quarts and you will only be able to add about half the approximate 16 quart refill amount.

The block should always be drained with every coolant change.

Coolant should be added slowly and the car bounced up and down after every 2-4 quarts. Once full start the engine and monitor the level. When the thermostat opens the level will drop, so add as required to bring to the full level, then install the cap and drive the car around the block a couple of times. Let it cool for awhile and check the level again. Also check and correct the level for the next couple of heat cycles until it stabilizes at the OE recommended level specified in the owners and service manuals.

Duke

Thanks Duke,

I will drain the complete system in the future... i beleive if there was any air in the block it is now out.. I have kept toping up the rad after each drive around the block for at least 4 trips.. letting it cool down each time.

I will be adjusting the timing tomorrow, I was planning on setting the dwell to 30-32 degrees and will attempt to advance the timing as much as possible.

Any recomendations on what brand/model and where is best to pick up the distributor?

What do you mean to set it up to '65 SHP/FI specs?

Thanks again,

Joe

[Joe P.]

Re: Iratic temperature swing - overheating

Drain the complete system...........especially and including the block, by removing both drain plugs. Run some coat hanger wire into both drain holes to be sure to clear all of the cr*p out of the lower block (a dirty/plugged lower engine block water jacket will NOT cause your problem, what it WILL do is cause a rise in your oil temp.).

Look for the coolant capacity in your owners manual. Take note of how much fluid a dry fill takes, and you'll know, for sure, what you've got.

The thermostatic fan clutch should be fully engaged after your road test, and it should be "roaring" when you gun the engine.

I have never seen a system air bound to the extent that it would prevent (about) 1/2 gallon of coolant from entering the system (assuming your engine block is already full)!

Is the engine still running "rough"? Do you have a "miss"? Timing could be a bit retarded, but hard to believe that it would boil over so quickly unless there is GROSS misadjustment.
Is your valve lash set properly?
Are your head gaskets intact?
Could be a lot of things.

A sure fire check for exhaust leaks into the cooling system is to remove the thermostat, remove the fan belt, fill the engine to the thermostat flange in the intake manifold and run the engine briefly while looking for bubbles in the thermostat opening.

THanks for your input Joe,

The car is running well now, it seems it was just on start up after a long sleep. It isnt misfiring, and there is no pinging. The clutch does screem when i gun it at idle. The engine was rebuilt 2 years ago, and has the fluid has been changed a few times since, I must admit i didnt drain the block competely, but will in the future. I beleive all the air is out and the system is full now.

Thanks for the good tip on checking for exhaust leaks.

I am going to try adjusting the timing tomorrow and will order a new wire for the temperature sending unit, I also picked up a seperate gauge locally that i am going to try to rig with the gauge in the car to compare temperatures.

Joe

[Duke W.]

Re: Iratic temperature swing - overheating

Thanks Duke,

I will drain the complete system in the future... i beleive if there was any air in the block it is now out.. I have kept toping up the rad after each drive around the block for at least 4 trips.. letting it cool down each time.

I will be adjusting the timing tomorrow, I was planning on setting the dwell to 30-32 degrees and will attempt to advance the timing as much as possible.

Any recomendations on what brand/model and where is best to pick up the distributor?

What do you mean to set it up to '65 SHP/FI specs?

deg.



Duke

Thanks again,

Joe

Any single point tach drive Delco single point distributor will do, and I'm sure they are readily available from the usual used Corvette parts sources. In fact, you may even be able to work out a trade deal. Give it a good overhaul (see archives). Depending on year/model it will have anywhere from about 20 to 30 degrees total centrifugal. You if you can ID the dist. part number, someone here can give you OE specs.

You can grind out the advance slot to increase centrifugal or braze/epoxy it up to decrease.

Upon reassembly install a "B28" VAC and hook it up to a full time vacuum source. Get a spring kit and install the lightest springs that the engine will tolerate without detonation and set the initial so that initial plus full centrifugal equals 38.

The '64/'65 SHP/FI spark advance map is 0 @ 700, 24 @ 2350; 0 @ 4", 16 @ 8", which is a good map for any year engine with a SHP type cam. The centrifugal may be a bit too aggresive on some depending on the actual compression ratio, so it may need to be slowed down. Final tuning of the centrifugal to optimize without detonation on a specific engine must be done on that specific engine.

If you don't feel comfortable with this, google "lars grimsmund", contact him and he can set up a distributor pretty close to optimum if you can give him specific details of the engine such as cam and actual compression ratio.

Duke

[Joe P.]

Re: Iratic temperature swing - overheating



That was enough to give me some piece of mind..

Late yesterday a friend came over with a fancy digital snap on timing light..

Duke the timing was set at 33, at an idle of 1300 rpm and after some discussion and another test drive. We decided based in part on your recommendation to leave the timing at 33 for now. The car starts great and runs well..

I ordered a new wire connecting the temperature sending unit to the gauge. I am hoping this will resolve the gauge fluctuation. The weather was cooler in the last few days, so I am going to keep the "MacGyver " gauge in place for a hot day..



BTW, I dont plan on any permanent "MacGyver" aka BUBBA fixes.. purely for troubleshooting..

Thanks again for all the advice always greatly appreciated

Joe