New thermostat. Top radiator hose is boiling and bottom radiator hose is cold

[zaid3ssaf]

So Here's the deal, My 02 Bravada was running little hot (about 217F), and since the normal operating temp is 190-215 F, I decided to change the thermostat (just being over cautious and little stupid). Anyway, now she runs even hotter (220-223 F) with the new thermostat (Dorman 902-800). After driving for 20 minutes you could hear the coolant bubbling (or boiling), and the lower hose is not even warm. https://photos.app.goo.gl/MQ8bWLeGF5ahP18ZA

- I flushed the coolant and filled it with tap water. Ran it till it reached temp then drained coolant. I did that twice. Then on the final round, radiator was drained and radiator and reservoir were filled with dexcool.

1) Is my thermostat bad? or my temp sensor?
2) How long should the system be "burped" to get all air pockets out?
3) I topped the reservoir when the engine was cold. Is this okay?
4) I also heard ticking noise that comes and goes away. Not sure what that is. https://photos.app.goo.gl/7XuWyDWc8jC3Aptx6

@Mooseman

 

[Mooseman]

Hi and welcome! Glad you joined us from the dark side.

I have no idea about Dorman thermostats if they are any good. We tend to stick to ACDelco for proper operation. It might be OK but no way to know for sure.

The bubbling could have been trapped air but this system is usually easy to burp. Once is usually enough. The reason the lower hose is cool is because it's a reverse flow system. Cooled coolant enters the engine by that hose controlled by the thermostat. The upper hose would be the one that gets hot as it exits the engine.

We usually recommend replacing the temp sensor at the same time as the thermostat as a preventive measure since it is as difficult to reach as the thermostat. It may still be good. You could check its accuracy with an IR temp gun against what the PCM is reading.

217f isn't overly "hot" but a bit warmer than usual. Mine hangs around 198-203f but does get warmer while towing. As mentioned over there, check your fan clutch operation. At that temperature, it should be engaging a bit. It starts at 210f.
Fan speed command chart
How to test the electro-viscous fan clutch

Filling the reservoir cold is the proper way of doing it to the cold level. It may go down a little more as air escapes into it and coolant is drawn back into the rad as it cools.

The ticking could be the fan clutch. Or possibly the exhaust manifold. They have a tendency of cracking or just leaking at the head.

 

[zaid3ssaf]

Hi Mooseman,

I'm glad to be here after being from the waste land of trailvoy. I edited the post with new links. One shows the bubbling sound and the other shows the ticking sound.

I will probably replace the thermostat with an ACDelco. I didn't change the sensor cause I've seen people snap them and aluminum heads scare me.

I will check the fan clutch operation tonight. I remember that the fan speeds up noticeably when the engine gets warm. But I'll follow your method and let you know.

I've never heard the ticking before so I dont think its an exhaust leak. For the bubbling, I have purged air out of the system for 20 minutes so I dont think its trapped air. When I ran the engine with distilled water couple of times, I didn't drain the block because it meant I had to remove the thermostat (that I just installed). So I ran water till no old coolant was left and then filled it with dex-cool (prediluted). Do you think I could have diluted the 50/50 mixture so much by leaving distilled water in the block?

 

[Mooseman]

If you filled with 50/50, it might have been a bit diluted so it's possible it was boiling a bit, especially if you had the cap off and not under pressure.

And if you check lower in that thread, an additional method to check the fan clutch is to jump the "relay" to send full 12v to it. If it locks up and sounds like a jet engine, it's working. If it just keeps freewheeling, it's toast.

 

[mrrsm]

Welcome to GMT Nation...

Nice Job with Posting those Diagnostic Videos!

This link will take you to my "Flickr-Bucket" for some ACDelco vs. Stant Thermostat OEM Side By Side Comparison images with their Part Numbers and appearances to compare with your Dorman Thermostat:

GM_04_42L_NEW_ENGINE_PARTS

This Album contains images of Brand New Engine Parts and Components for the Complete Rebuild of the GM Atlas LL8 4.2L Engine for the years 2002-2004.

www.flickr.com

 

[Mooseman]

Had a look at the Dorman at RA and it's made by Motorad. Not good results from it and not made the same as original.

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I used a Mahle/Clevite as it looked the same as the ACDelco. It's been fine since Nov. Mine came without the crimp bent pipe but from what I can tell, ACDelco also went this way. It had the correct jiggle valve for air bleeding.

 

[Mooseman]

Just updated the fan clutch test thread with additional info to jump the relay for testing.

 

[zaid3ssaf]

@MRRSM @Mooseman. Thank you guys for the info.

I took both thermostats out and did the boiling water test. The dorman thermostat didn't do so well. took forever to open and forever to drain whats in it once the it was lifted out of the water. My ACDelco part gets here today and I'm excited to put it in. The old thermostat wasn't ACDelco so hopefully It'll drop below 215F with ACDelco. I'll let you know and mark the post as solved if it works.

Edit: it started snowing. Gosh darn it, Iowa!

 

[zaid3ssaf]

So I just put the ACDelco thermostat in, and son of a gun, it not overheating anymore. It stays at little below 210F on the gauge and on the scan tool it stays between 197F and 203F. Right on the money!!

For anyone reading this (TLDR) I had an overheating problem which I ruled out as a bad thermostat. So I replaced it with another Dorman thermostat (which also turned out to be defunct. What a coincidence) and that made the problem even worse. That made me think that other parts of the cooling system are going bad. But no, it was the thermostat. Always buy OEM for 10 bucks extra you get what you pay for.

Thank you @Mooseman and @MRRSM

 

[Mooseman]

Excellent. As a precautionary measure, check your fan operation before the warm weather arrives. They are failure prone and usually doesn't manifest itself until the warm weather arrives.