Question for our Engine Experts

[Larry E.]

Believe my subject has been discussed here before but can not find under "search". My questions applies to
all Chevy engines. Here goes: Have a 77 LS9 (350 S/B) Chevy P/U Shortbed. Ever since new after a ride on a hot
summer day I have noticed once parked in the garage overnight the top radiator hose "collapses" which I presume
is suction in the hose. When I open the radiator cap it turns back to normal. This truck does have the two seal cap
and the racovery tank from the factory. IIRC one of the fixes is to drill a small hole on the flat portion of the thermostat.
Here is my questions: 1) What causes this condition; anybody else have this problem?
2)What a some simple fixes for this problem? Does the small drilled hole in the "stat" do the trick?

Thanks in advance; Larry

[Joe R.]

Re: Question for our Engine Experts

Larry,

I believe that usually happens on the lower radiator hose. John Hinckley's fine cooling article in the latest Restorer covered it. I guess you could put a spring in the upper hose to keep it from collapsing.

Joe

[Terry M.]

Re: Question for our Engine Experts

Larry,

I believe that usually happens on the lower radiator hose. John Hinckley's fine cooling article in the latest Restorer covered it. I guess you could put a spring in the upper hose to keep it from collapsing.

Joe

With a coolant recovery bottle, which it sounds like your truck has, when the engine cools the coolant contracts and creates a suction (vacuum) in the coolant system. On cool down a properly operating radiator cap will allow fluid from the recovery bottle to flow into the coolant system and take up the volume of shrinkage of the liquid in that system.

The reason the lower hose has the "wire spring" is because it is on the suction side of the water pump and during high speed operation there is a chance the water pump will pull the lower hose closed.

Buy and install a new radiator cap for your truck and the collapsing upper hose will be a thing of the past.

[Michael W.]

Re: Question for our Engine Experts

The 'hole in the thermostat' is for a completely different issue and the fix doesn't do much for that either.

[Duke W.]

Re: Question for our Engine Experts

I'm with Terry. The vacuum relief valve in your radiator cap is likely not functioning properly, so a new radiator cap should do the trick. Also make sure the cold level in the coolant recovery tank is in the proper range. It probably has at least a "full cold" line.

Duke

[Joe L.]

Re: Question for our Engine Experts

Larry------


The radiator cap you need is a Delco RC 81, aka GM #25661994. About 10 bucks.

[Larry E.]

Re: Question for our Engine Experts

OK; will order the new Delco RC 81 from the Local Chevy Dealer today. Thanks to all that responded.
You guys are the best. Joe: Thanks for the Part#. Larry