overheating solution?

[Don Izzo]

While doing the couch potato thing this past weekend, I stumbled onto a show on the Discovery Channel about a street rod that was being built by "Boyd Cottington" (sorry if I spelled his name wrong) After the car was finished they fired up the engine for the first time and it pinned the temp gauge. Boyd told his crew that they had a vapor block or air bubble in somewhere in the block and would have to vacume the block to get it out. They proceeded to attach some kind of vacume device to the block and after 2 attempts the car no longer overheated and the temp gauge read normal. Anyone else see this show, and can you tell me more about this process? I would like to try this on my 1960.

Don

[Dave S.]

Re: overheating solution?

Don,
It is a common problem. There are several ways to prevent it from happening. I have had good luck with filling the system through the thermostat hole and then installing the thermostat and housing last.

[Clem Z.]

Re: overheating solution?

i remove the thermostat and housing BUT i fill from the rad,that way the trapped air is pushed out the thermostat opening in the intake manifold. then install the thermostat and housing and continue filling the rad.

[Jim T.]

Re: overheating solution?

Another method is to drill one or two small holes in the actual thermostat so it will let air escape when refilling the coolant system. This provides a small bypass for the coolant during normal engine operations until the thermostat begins to open. I have modified mine.

[Terry M.]

Re: overheating solution?

At school we have a vacuum pump which is designed for evacuating air conditioning systems. This same pump can draw a vacuum on a coolant system. We use a sponge ball (kids toy) with a hole punched through it. Push a hard plastic tube through the hole, and place the ball with tube over the coolant filler port (radiator or expansion tank). The ball seals at the place where the radiator cap normally seals, and draw a vacuum on the plastic tube. I would think that with some ingenuity one could use manifold vacuum to do the same thing, just be sure not to draw any coolant into the engine.
Some cars need vacuum to draw the air out of newly filled power steering systems as well. Vacuum can be a handy tool.

[John H.]

Re: overheating solution?

That's how it's done in assembly plants at 70 per hour - vacuum is applied at the fill cap opening (hoses immediately go flat), and coolant is charged at 35-40 psi into the system while it's under high vacuum. Same process is used for brake fluid, power steering fluid, and A/C refrigerant. Brake bleeders are never touched - it's all done through the master cylinder reservoir cap.

[Duke W.]

Re: overheating solution?

One of the basic design rules for a coolant system is that the fill point should be the highest point of the system. If not, the system may be tough to bleed.

When filling a system the thermostat is usually closed so the liquid fills the engine from the bottom, but often leaves an air bubble at the top of the engine because there is no place for it to go. Drilling a very small hole in the thermostat will allow it to escape.

Even if there is an air bubble in the engine it will usually self purge as long as the coolant level is high enough to reach the pump level. Once the engine is started and the thermostat opens the air bubble will be pushed out of the engine to the radiator and escape through the fill port.

On C2s with aluminum radiators there is a vent at the top right of the radiator with a hose connection to the remote supply tank. This is the vapor vent, and any design with a remote supply/fill tank will have a similar vapor vent.

When filling a cooling system, do it slow as this will usually minimize the size of the bubble that forms at the top of the engine. Once full, start the engine with the cap off. When the thermostat opens the level will usually drop as the air is pushed out of the engine and into the radiator where it can vent. Add coolant as necessary.

Some of the toughest coolant change jobs are mid-engine cars with front radiators. Toyota thoughtfully placed bleed valves at the top of the radiator and near the top of the heater core on my '91 MR2, and these must be open when filling the system. Since the tranfer pipes are along the bottom of the car, without the bleed valves the radiator and heater core would never fill. Even with this good design and slow filling, the system will pull a quart of coolant out of the overflow bottle over the first few heat cycles as the remaining air is purged.

Corvettes and most front engine cars are a piece of cake. Be thankful you don't own a Pantera. I understand they are a bear to fill because they don't have bleed vavles at the radiator and heater core.

Duke

[John H.]

Re: overheating solution?

My Ferrari was the same way - rear-engine, front-radiator, system held 28 quarts of coolant with the pair of 2" aluminum transfer tubes that ran front-to-rear. Had bleeder valves on the radiator, heater cores, and the thermostat housing, plus the fill cap on the rear/high-mounted supply tank. Changed coolant annually, no problem if you followed the manual and used the bleeders; without the bleeder valves it would have been a real bear to "burp" the air out of it.

[Bill Jackson]

Re: overheating solution?

My 71 Pantera with a stock radiator has little petcock type vents at the top of the radiator. I'm not aware of any for the heater. As I recall, the shop manual says raise the rear of the car about 12"; open the radiator vents; fill slowly till coolant flows from the vents.

[Terry M.]

Re: overheating solution?

The 1992-1996 LT1, with its reverse flow cooling system, can also present coolant fill problems even with a single thermostat housing mounted air bleed. Elevating the nose of the vehicle - that is raising the supply tank - can help, but even at that, a quart of coolant will flow into the engine on the first few heating and cooling cycles.

[Mike H.]

Re: overheating solution?

Don,
They were probably using a tool like the one shown in the link. Most tool trucks carry a like unit and probably NAPA. I bought mine from a Carquest jobber and it is a rebox of the AirLift unit. Great tool!
Mike




AirLift