The Stovebolt Site Forums The Shop Area Engine Shop Overheating '68

I am new to this board, so holler if I should be posting this to another spot or if the info is out there.

I have a '68 Chevy Pick-up with a 350 in it. It was running fine, until the power steering pump bracket came loose and the fan hit the pump, sending fan shrapnel through the hood. That is fixed, and I replaced the brackets with a '66 Corvette kit so that the pulleys now line up.

After the "event", I also had a leak out the back of the water pump, so I put in a new aluminum one from JEGS.

Now, I have a new problem. The truck gets up to temp, and then overheats, without the thermostat opening. Then, when the gauge says the truck is overheated hot, the thermostat opens, and it cools down. But then, the top hose collapses on itself, and the truck heats back up.

I plan to put in a new thermostat tonight, but I am wondering if that is going to solve the problem with the collapsed hose?

Also noticed the air cleaner has oil in it - can you do engine damage from just a few overheats?

Thanks for any info.
Dan

MAER,

Welcome to the Stovebolt. I would guess you have air trapped in the system, but replacing the thermostat would be a wise move too. Exactly why your top hose collapses, I am not sure...maybe the pump is high output, and because the stat isn't open, the pump is creating a vacuum on that side of the system.

Drilling a hole in the flange of the new thermostat might alleviate any future 'burping' problems.

The air cleaner can collect oil from a crankcase venting system that might be plumbed into it. Check your PCV valve and any related hoses.

Stuart

You didn't put on a water pump that works in the reverse direction did you? It seems to me I read that a reverse pump is used on some serpentine belt systems. Just a thought.

A top hose collapsing does sound like a reversed water pump situation, especially when it doesn't collapse until the thermostat opens.

Would a water pump run in the reverse direction be efficient enough to pump much water at all? If the thermostat were open, there would be no restriction to flow...where would the pressure differential be to force a hose to collapse?

Just thinking out loud on this one! :confused:

Stuart

I'm just thinking out loud on this, so don't assume I know what I'm talking oabout. But here goes.

The pump would push the coolant in the wrong direction. The coolant would also be flowing through the thermostat in reverse. Could the flow of water running backwards through the thermostat pull it shut? If so, the negative pressure would collapse the hose.

when they have the wrong pump they will overheat, but he says he has Corvette or old style (short pump)brackets, serpentine pumps are only the long or "new style" 68-up cars(except Vette) & 73-up trucks
It sounds to me like a bad t-stat or even one in backwards can act like that.

Thank you all for the thoughts!

I believe the new water pump pumps in the same direction, but it might be "high output." The JEGS catalog was not clear on that.

Is there such a thing as a "high output" thermostat? Or, how big of a hole do I drill in the flange?

Should I just run it without the thermostat for a while to see what it does?

Is there such a thing as a "high output" (i.e. stronger) hose?

MAER,

I think a standard thermostat is designed to flow as much or more than would be required for the engine. Drilling a 1/8" hole in the thermostat flange would allow any trapped air to pass and guarantee that the thermostat was surrounded by water.

A good radiator hose has lots of strength. Lower hoses sometimes come with internal springs, but I don't know about upper hoses, as they are on the discharge side of the pump. If yours feels soft and spongy, it might need to be replaced.

Jegs does show a high output pump, but you would have had to order it specifically...and you would probably would have known. I would do the thermostat, maybe a new top hose, check the radiator cap, and give it a try. Running it with no thermostat would be counter productive.

Stuart

Thanks!

I am in agreement with the reverse flow pump. The thermostat would normally see hot water coming from the engine and stay open, once opened. If the water is coming from the radiator, the thermostat would cool down again and close.
Jegs sells aluminum pumps that are made to replace conventional pumps, but are reversed to be used with aftermarket serpentine setups.
Chevy pickups did not get the 350 until '71. What year 350 do you think you have?

It wouldn't be the first time a part got put in the wrong box.