Hi there. Sorry that I do not have a problem with a Chevelle, but I am desperate looking for help on my Silverado Pickup 4x4 with a TBI V8 350cid engine.

The last owner told me that I needed to change the thermostat in the engine and it was running without that now. Tried to install a new thermostat, but then the engine overheated at once.

Then I changed the water pump, did not help. Installed a new radiator, did not help. Took the car down to a local garage, they checked if the head gasket was gone, but no… Installed a new cap on the radiator, still not any change… When the thermostat opens, the radiator host are getting flat???

The engine runs like a clock without the thermostat, and do not use any water… I have used the truck for a while, and since the engine is not running with the right temp, it uses a lot of gas! I want to convert it to run on Propane, but need to fix this problem first.

Can any one help out???

Not to insult your intelligence.... but are you sure you put the thermostat in the right way? If you put it in upside down it will never open. Do not ask how I know this.

ALSO.... are you saying that your hoses ARE collapsing or you think they are collapsing? If so I would find news one and put them on. A collapsed hose will obviously restrict fluid flow.

Easy test
the top hose will be soft till the thermostat opens if the stat in is in upside down this will be evident if the hose never gets hard ... the bottom hose is the suction side and should not be soft or colaps .. this wiuld be hard to see at idle but when at highway speeds when suction is higher .. will cause a over heat condition .. back in the day there was a spring in them not in todays market

Along the same idea as the others for the upside down thermostat... There should be an arrow on the side of the thermostat to indicate the flow of water. The water will flow "up and out" out the thermostat housing. So the arrow will point up.

this way, the bottom of the thermostat is the more "square" like part, while the top side is the triangular / tapered / nose-cone part.

It is possible that your thermostat isn't working like it should. you can actuate it by hand to see how it opens. You can even drop it into a pot of boiling water to visually watch it open. I think water boils around 200 degrees F, and your thermostat should be something like a 180*F, not sure on those numbers.

Along the same idea as the others for the upside down thermostat... There should be an arrow on the side of the thermostat to indicate the flow of water. The water will flow "up and out" out the thermostat housing. So the arrow will point up.

this way, the bottom of the thermostat is the more "square" like part, while the top side is the triangular / tapered / nose-cone part.

It is possible that your thermostat isn't working like it should. you can actuate it by hand to see how it opens. You can even drop it into a pot of boiling water to visually watch it open. I think water boils around 200 degrees F, and your thermostat should be something like a 180*F, not sure on those numbers.

The thermostat is NOT the problem. I have tryed 3 different thermostats. New radiator and radiaorcap. New waterpump.. The engine is not using any water and runs nice without any thermostat.

I see you replaced everything but the hoses. I think Jeff hit on it. Without a Tstat the system free flows. When you install the Tstat you are creating a restriction. This may be causing the lower hose to collapse. Try replacing the hoses with heavy duty or steel braided hoses.

I see you replaced everything but the hoses. I think Jeff hit on it. Without a Tstat the system free flows. When you install the Tstat you are creating a restriction. This may be causing the lower hose to collapse. Try replacing the hoses with heavy duty or steel braided hoses.

Hi, I have now tryed out every tips.... I used steel hoses, but without any luck. The engine is still overheating.

Put everything back together without the thermostat, and I am now driving it to work every day without any problemes... But when the winter start, I need to have this problem fixed!

I am now looking for time to take the engine out and see if there is any reason that the water do not flow right...

Easy test
the top hose will be soft till the thermostat opens if the stat in is in upside down this will be evident if the hose never gets hard ... the bottom hose is the suction side and should not be soft or colaps .. this wiuld be hard to see at idle but when at highway speeds when suction is higher .. will cause a over heat condition .. back in the day there was a spring in them not in todays market

I bought new hoses from Oreilly's for my new engine and they asked with or without a spring, so I got one with the spring??? :confused:

Have you tried a high-flow thermostat like a Stewart? It's only $10.

Sounds like you have ruled out just about everything.

Before you pull the engine etc, I would check the water pump again. I have seen the impeller break loose from the shaft. Many pumps have the impeller tack-welded to the pump shaft and I seen them break loose, even on a new pump. Some impellers are a press-fit on the shaft and can come loose too. When the impeller comes loose, everything works except no water is moving through the engine/radiator.

When the thermostat is installed, there is a lot more "pressure" on the impeller to move water. That might be why you are running hot when the thermo is installed. When the thermostat is removed, it does not take much to move the water and a loose impeller might function just enough to keep it cool.

It the engine really overheating or just possibly a bad sending unit thats causing the gauge/light to malfunction when the coolant is at a more constant temp (stat installed)?

Have you changed the rear end gears in the truck? Do you still have a clutch type fan? Fan shroud still in place?

When the thermostat opens, the radiator host are getting flat???




The lower radiator hose should have a spring(coil) inside it to prevent it from collapsing under the suction. When you change hoses you have to take the coil out of the old and install it into the new one. Alot of people never do this, and it causes problems. Maby this is your issue.

edit: Woops I see already got a hose with the spring.

Here's my take....I have seen this before.

The or radiator (or engine block) is plugged, corroded or scaled? Since all the water pumps are centrifugal type, when the thermostat is out....this is just enough system resistance removed to keep adequate flow to cool the engine. Add the thermostat and the system slows appreciably and then overheats.

Flushing might help...but let me ask a question first. Has this vehicle EVER had Dexcool in it? Or ....was it converted from Dex to regular antifreeze? Is there evidence of a milky semi hard substance on the radiator cap or any other place. My quess is that someone might have put something in the radiator that the Dexcool did not like...and plugged the system somewhere.