Vehicle loves to overheat?

MIKE 376

MEMBER
2003 PONTIAC MONTANA
3.4L
V6
2WD
AUTOMATIC
18,000 MILES

Usually within a mile after a cold start after a minute or so of warm up. This is an ongoing problem.
Work that was done: replaced T-stat, replaced water pump, had head gasket checked (it was okay). Replaced drive belt. All hoses okay. Cooling fans had issues but fixed to run full time. Heaters work normally and put out hot air.
Naturally the next step is replacing the radiator. But after reading a few of the Q&A here and other car sites, I am suspecting the coolant itself. Currently has DexCool in it which can cause blockage.

So, my Question is, 'Can a flush and fill and replacing the DexCool with Prestone Green coolant potentially fix the overheating issues?'

Note: the mechanic could get it to run within the normal temperature range, but it would start overheating as soon as I would take it home.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

The only time DexCool becomes a problem is if it is mixed with a different type of coolant. If it has always had DexCool, that isn't the issue.

If you want to flush it and replace it with a traditional green coolant, you can do that. However, you need to totally get all the DexCool out of the system first.

As far as the radiator, if that is a question, I would flush it to see if it helps. Even if it only helps a little, you will know there is where the issue is coming from. Here is a link you may find helpful:

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

When the engine overheats, do you hear the coolant boiling, or is there steam coming from the engine? With everything you have already done, I'm questioning if the temperature sensor is good.

Also, let me know what was done to check for a head gasket issue and when it didn't overheat for the mechanic, was it parked?

Let me know,

Joe

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Thursday, July 14th, 2022 AT 10:07 PM

MIKE 376

MEMBER
3 POSTS

Thank you for your reply. The mechanic used a combustion leak detector hooked up to the radiator fill neck. He found no issues there. The mechanic was able to drive it without it overheating. Stayed in the normal range. But a week or so later when I picked up the van, it overheated within two miles.
When it overheats, the coolant boils back into the reservoir. No steam is noticed. I did check the inlet (water pump side) and outlet (T-stat) hoses, the outlet hose was very hot, but the inlet hose was cold or cool to the touch.
I suspect the radiator has an obstruction that seems to move through the system causing periods of running normal temperatures then periods of overheating. I too suspected a faulty temperature sensor but with the hose heat/cool issue, I defaulted back to a radiator blockage.
Note: the previous owner had replaced the freeze plugs and wired the cooling fan to a switch in the cabin. Apparently, he had issues with it too. The switch fan worked for a few months then it was not able to keep the engine cool.
Thank you in advance for your advice.

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Friday, July 15th, 2022 AT 9:02 AM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

I feel it has to do with the radiator as well. Something could be moving around causing a restriction.

If you think about it, the prior owner may have added some form of stop leak in the system when the freeze plug was leaking. There are certain types that can cause restrictions or blockage.

Try flushing the radiator at home. Get a good product from the parts store for the procedure.

Let me know if that helps or if you have other questions.

Take care,
'
Joe

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Friday, July 15th, 2022 AT 9:36 PM

MIKE 376

MEMBER
3 POSTS

Joe, your advice will be the current plan. Since I am going back on the road for a few months, I am going to let the mechanic do a super flush on the whole system including flushing out rear cabin heater system and just go green instead of using DexCool. Will update you with the results.

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Sunday, July 17th, 2022 AT 6:39 PM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

I feel that would be the next step. Make sure to tell him that all DexCool needs to be removed before changing to a different type.

Going on the road for a few months sounds rough. Ugh! Regardless, take care of yourself and I look forward to hearing the results.

Be safe,

Joe