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chevygeorge, ASE Certified Technician
Category: Chevy
Satisfied Customers: 53
Experience:  GM Technician for over 25 years
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I'm a mechanic from years ago who has moved on to a new

Customer Question

Hi Pearl, I'm a mechanic from years ago who has moved on to a new career, but I have a chevy venture that is overheating. There is no coolant in the oil, and the system is putting out gasses. A local shop says it's the head gasket, but have never seen a head gasket make an engine overheat like this. It overheats in minutes. When I made sure the system was full of coolant, it got real hot, but did not overheat. I think this is a plugged radiator because the coolant is brown, like someone used Bars-Leak at some point, and I find build-up of brown crap everywhere. I just don't believe it's the head gasket, I think the radiator is plugged and not cooling down the coolant.
JA: Have you checked the coolant? Have you checked for a leak in the cooling system?
Customer: I replaced the thermostat and the temp sensor to make sure I wasn't getting bad readings or a stuch thermostat. But to overheat in less than 5 minutes, that can't be a head gasket. Driving the car makes it overheat in a longer timeframe, but only minutes.
JA: What year is your Venture?
Customer: 2002
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: look up in text
JA: Anything else you think the mechanic should know?
Customer: Just that the radiator cap, and every part of the inside of the coolant system is full of brown gunk. Its not oil, it is hard and has to be chipped away.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Chevy
Expert:  chevygeorge replied 1 year ago.

Hello, My name is ***** ***** I'm here to assist you today. If I understand correctly, You have done a combustion gas test of the cooling system and it tested positive?

Customer: replied 1 year ago.
No, i dont have that equipment here.
Expert:  chevygeorge replied 1 year ago.

The brown sludge is what happens to dex-cool breaks down and comes in contact with air in an open system. It's been responsible for multiple heater core restrictions on many models. It is very likely it has caused restrictions. Have you checked the temp difference between the top and bottom of the radiator? That would give you a quick and easy check to determine radiator flow.

Customer: replied 1 year ago.
My FLIR is at work, and i cant reliably check it for temp differences.And brown coolant, i get it, but hard brown crust on the radiator cap? Im having trouble believing that it is broken down coolant. Im thinking tbe radiator is blocked and its not cooling the coolant. Once i filled the system, got the air pockets out, it ran over normal temp, but was stable. It didnt overheat like previously.
Expert:  chevygeorge replied 1 year ago.

If the radiator is majorly restricted, it should be easy enough to check the temp with your hand. The 3.4 L engine in your Venture is sometimes difficult to purge the air in the cooling system. They tend to develop the air pocket in the back head(where the temp sensor is located) and give skewed readings. I would recommend a good chemical coolant flush, after thoroughly flushing with a garden hose. It may be necessary to disconnect the heater core and back flush with the garden hose to prevent blockage. I've saved a few S10;s this way. Head gaskets are pretty solid on these, unless the engine has been severely over heated.

Expert:  chevygeorge replied 1 year ago.

GM says that is what happens when tap water is added to dex cool over time. Very common on S10's of the era. Sometimes the build up is so great you have to clear the radiator opening.

Expert:  chevygeorge replied 1 year ago.

When you refilled the system, did you open the air bleeds? It can be done while the vehicle is running also. I'll attach the procedure to see the locations.

Expert:  chevygeorge replied 1 year ago.

Here's GM's document on the S10 flush procedure pertaining to the rust/sludge in the cooling system.

I would start with a flush and bleed, and proceed form there.

Please take the time to rate my service today, and feel free to let me know if you have any further questions. Please note, we can continue our conversation even after rating. Thank you, George.

Customer: replied 1 year ago.
I bled it it. I refilled it. There is no coolant in the oil. The shop wants to do a head gasket and a radiator. Im thinking do the radiator first to see if it fixes the overheating. Then, if a gross hole in the head gasket exists, we deal with that after. But to run hot, but stable, means the engine is not cooling. That is not a gasket issue, that is a cooling issue. Loss of coolant over time would be the issue with the head gasket, but not overheating.Does that logic sound right to you?
Expert:  chevygeorge replied 1 year ago.

That seems like perfect logic to me. If the head gasket was bad, you would have A. Have coolant in the oil. B. Have coolant leaking, or C. Have coolant burning out the tail pipe. GM recommends a VAC-N-Fill equipment for all coolant refilling these days, due to air issues. When first warming up, Is the upper radiator hose pressurized? The radiator would be a logical start, due to the sludge.

Customer: replied 1 year ago.
the upper hose is presurized. Im telling them to replace the radiator, power flush and fill, then let the kid drive it around town to see how much the head gasket is affecting the system.
Expert:  chevygeorge replied 1 year ago.

It sounds like a logical starting point. Thank you, George