SB still running hot....

[Jim V.]

Thought I was beyond my run hot situation back in the spring. Guess not....its back.....!!!)$#$%$#%.

QUESTION>>>Is it normal for coolant to flow to the supply tank from the top of the radiator thru the radiator to supply tank pressure equalizer hose at RPM?????

With the supply tank cap off, I can see coolant entering the supply tank when rev-ing the motor from idle (t-stat open). However, at idle, there is NO flow to the tank thru the rad-S-Tank hose. Earlier I thougt I fixed my run hot by tightening a clamp on the lower rad hose preventing a suction side air leak to the pump. Guess not......

Seems to me this rad-to-tank flow effectively bypasses the radiator by recycling hot coolant from the t-stat,upper rad hose, top of rad, rad to s-tank hose, back to the pump via the heater hose.

Can someone run a test to see if this is normal on a functioning SB OE cooling system? Can I still have a suction (lower rad hose) side problem....hmmmm

Just a recap...
Temp Verified w/ IR gun (200F @ tstat hsg, 220@gauge)
OE pump, fan, clutch, rad., t-stat..
NEW DEWITTS rad
New checked t-stat
OE rebult w-pump
pressure tested c-system NO leaks, No pressure flutter
cylinder leak down test NO leaks
coolant CO2 test NO CO2 in coolant
timing good
New adjusted GM fan clutch
Stock shroud
Stock t-sender
OE lower hose WITH spring

Thanks again!....
JimV

[Timothy B.]

Re: SB still running hot....

Jim,

You may be noticing the coolant being circulated from the water pump to the heater core when reving the engine looking into the overflow tank.

I think the small top hose will not pass any coolant unless there is coolant expansion in the radiator and at that point fluid is allowed to overflow into the side tank. I am not sure when this condition occures but I will be corrected if wrong. I think the engine would be very hot for this to happen.

Did you check your pressure cap to see if it holds pressure? I can't think of any reason the car will not maintain approx 180 temp. Are you sure there is enough coolant in the system? If the cap does not hold pressure it will puke coolant because it will not allow pressure. Do you recall the inital timing and did you make sure the V-advance is not ruptured.

[Jim V.]

Re: SB still running hot....

Tim,
Coolant is returning to tank from rad not via the heater core circuit. With cap off it is easy to see the flow from the rad via the tank hose into the tank.

Had a long thread over in CF in the spring on this same, turn out unresolved, issue.

http://forums.corvetteforum.com/c1-and-c2-corvettes/2323723-another-hot-hot-overheating-story.html

Timing is dead nuts....Vacuum and mech work fine

Suspect restricted suction side coolant flow issue.

Thanks

[Timothy B.]

Re: SB still running hot....

Jim,

I think your thinking is right on but with two radiators and several W/pumps how could any of these componits be suspect.

Does the system go under pressure when the cap is installed and engine hot? My thinking is that the pressure forces a flow through the radiator and the small radiator overflow hose is there to protect the radiator against excess volume by bypassing to the expansion tank. I think the fluid is flowing to fast to go through the radiator thus being forced back through the radiator overflow hose to the exp. tank.

It's doing what it is supposed to do, but why such excess flow..

With a replacement water pump that is drilled in the top for bypass there is a small 3/8" dowel to install in the pump so it bypasses to the top and I wanted to ask you if that could be in place with the original pump. I don't have one in hand to look at but I wanted to suggest to you. I think the water pump continually pumps to the heater core so if this circulation is not correct the pump volume to the radiator could cause the condition you see.

Sounds to me like the fluid is returning to the radiator and getting pushed back to the expansion tank instead of being circulated down through the radiator and back out of the lower hose, does that sound like a logical thing happening here? At idle the flow is not as great so the fluid cools properly through the radiator then at higher RPM some of this fluid is not being cooled by the radiator but instead forced through the small hose to the expansion tank..

Sorry for the long post, stop changing parts and take a break.. Time to think this one out, I know you will get some good suggestions here but it's time to figure what's happening.

[Joe C.]

Re: SB still running hot....

Did the engine run hot before it was rebuilt?
Were any other changes made to the config of the engine and its cooling system?
Fore-and-aft location of fan in the shroud is very important.
I wouldn't chase cooling system flow problems unless I had a good reason to believe that there is one.

Joe

[Duke W.]

Re: SB still running hot....

QUESTION>>>Is it normal for coolant to flow to the supply tank from the top of the radiator thru the radiator to supply tank pressure equalizer hose at RPM?????

JimV

That hose would be properly described as a vapor vent. It's purpose is to vent vapors to above the free surface of the coolant supply tank. That's why it is located at the top of the cold side of the radiator and the supply tank inlet is near the top of the tank. (Remember that the radiator is a cross flow design with hot coolant out of the engine fed to the top of the left side of the radiator and the outlet to the suction side of the coolant pump on the bottom of the right side.)

This design will purge air bubbles once the thermostat opens following a coolant change. It will also vent any vapor due to very hot coolant that is not condensed in the radiator - near overheating conditions.

It's normal for some coolant to flow through the hose as revs increase, which increases pump head, but the vent hose cross section area is so small that the amount of coolant bypassed via this vent hose is a tiny fraction of the amount the coolant pump draws through the outlet hose on the bottom, and this continous bypassing will very effectively purge vapor from the cooling system.

Duke

[Jack H.]

Re: SB still running hot....

Remember, when you REMOVE the rad cap, you've opened the system to atmospheric pressure! That's NOT how the cooling system was designed to operate...

[Jim V.]

Re: SB still running hot....

Yep...Initially I thought the radiator flow was top down. Being a cross flow, I now understand that both outflows on the passenger side of the rad are on the cold side of the radiator....therefore no bypassing going on.

Given atmospheric pressure at the tank with the tank cap off I can see why there would be a more significant flow thru the top hose to the tank.

Rats...still no closer to figuring this thing out. Sure acts like a head gasket issue, but there is no sign of CO in coolant at the tank. Hmmm.......Seems like the heat generation side of the equation is outmatching the cooling side of the equation.

[Joel T.]

Re: SB still running hot....

Jim;

I think you might have hit on the right point in your last post.... The heat and cool sides of the equation are out of balance.. You have been looking at the cool side, perhaps you should look at the heat side..

A local guy here in NJ picked up a '62 with a later model 327 which was running a distributor without vacuum advance.. the car ran HOT.... he went through all of what you are going through now... After much research he determined that the lack of advance at lower vacuum levels created his heating condition.. I probably have some of his materials in my files. The punch line basically said that without the vacuum advance spark was so late that the mixture would continue to burn as the piston traveled down the cylinder pushing more heat than normal into the water jacket... He installed one of those adjustable vacuum units (after I taught him the two in rule) and presto... no more issue.

I'm not saying this is your problem but I would be checking all this out on the ignition side... making sure that the correct advance at various RPMs.. I would also look to see if you have any sort of exhaust blockage (i.e. stuck heat riser valve).

Hope this helps...

Joel

[Jim V.]

Re: SB still running hot....

Joel, thanks for your help with the PM. Yep...timing and mixture do matter on heat generation!... I did look further into the heat generation side of the equation by going after potential vacuum leaks and idle mixture. Retorqued intake, carb to intate, and top of carb. Also reset idle mixture maximizing vacuum (19hg @ 700rpm).

Looks like i was running LEAN due to both a vacuum leak and lean idle mixture. Appears to be running much better and cooler at idle at least. Did noticed a brief temp spike however after some spirited acceleration. Needs some further miles to really get the final outcome.

regards