Cooling system question

91 Comanche, open cooling system

Just went under the hood to check something and noticed the upper radiator hose was completely collapsed. The truck had been sitting for about six hours, and had no overheading problems when driving this morning.

Popped the rad cap, heard some pressure escape, the cooling level was down a bit, so I topped it off, no more than a half-pint or so. The overflow tank level was higher than normal, about 1" from the top, over the FULL mark. Started it up, warmed it up to 210, no leaks but the overflow tank level went even little higher. Went for a drive, the temp gauge stayed normal. Returned, popped the hood, and the overflow tank was still about 1" from the top, way higher than normal. The upper hose still seemed mushy, but not collapsed.

Only thing I can think of is I might have a bad rad cap and it's not allowing the pressure after shutoff to vent to the overflow tank. But what would cause the overflow tank to be over the FULL mark, and the upper hose to collapse? The hoses are fairly new, and it's never done this before. Thanks, all advice appreciated.

The radiator cap actually has two valves built into it...

Pressure Relief Valve (PRV) - This is the valve that gets tested when you test the cap, and the spring under it determines the pressure rating of the cap. This is the valve that allows coolant to blow off into the overflow when it gets hot. It is the valve that seals against the filler neck using the black rubber disc.

Vacuum Relief Valve (VRV) - This is the valve that opens to allow coolant to pass from the overflow back into the radiator as the system cools. It is the silver disc in the middle of the cap - you can test it easily. Just take the point of a knife blade, slip it under the edge of the disc, and try to lift. It should come off the seat easily and with minimal effort.

Since you describe the upper hose as having collapsed as the system cooled, I'd be inclined to say that your VRV is sticking closed (which would also account for the uptick in the coolant level in the overflow,) and just replace the radiator cap. It's cheap enough - just replace it anyhow. Write the date you install it on the new one, so you know how old it is (always a good habit for maintenance items.)

Keep the collapse in mind tho - if your upper hose is soft enough to collapse under light vacuum, you may be looking at replacing your hoses soon.

Thanks Jon, that's what I figured. You da Man. Wonder if the hoses with the inner wound spring are still available at the stealer? This hose is aftermarket w. no spring.

comanche91 said:

Thanks Jon, that's what I figured. You da Man. Wonder if the hoses with the inner wound spring are still available at the stealer? This hose is aftermarket w. no spring.

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The spring is usually only put in the lower hose, since it's the suction hose.

If you really want to put in a support, go to a fluid power shop and as for "hydraulic suction hose support coil" - it's going to be a coil wound from flat stock, and they're usually stainless. It may be spendy, but it's going to be tough enough to use in several hoses - just move it when you change hoses.