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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4413
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Over heating and fans aren't coming on.

This answer was rated:

over heating and fans aren't coming on.

Hello, my name is***** it overheat when going down the highway or only at low speeds/stops? Thanks.

Customer: replied 1 year ago.

its doing it right now just sitting still. and it got to 221-229 and the fans still never came on

Do fans come on if you unplug the coolant temp sensor?

Customer: replied 1 year ago.

I haven't tried that yet

Check and let me know. Also let me know if vehicle overheats while driving down highway. Thanks.

Customer: replied 1 year ago.

dang it. its hard to get to

A long screwdriver may make it easier to disconnect but then reconnecting will be just as hard. Let me know when you get around to it, thanks.

Customer: replied 1 year ago.

they do come on with it unplugged

That would mean wiring is ok. How did bleeding coolant go? Did you ever get air out of system or did it seem to be a never ending amount?

Customer: replied 1 year ago.

yes I got it all out and I used the yellow burp funnel

Do you have scan tool to command low speed fans?

Customer: replied 1 year ago.

yes

Do they work when commanding them on low speed?

Customer: replied 1 year ago.

yes and relay 2 and 3

It sounds like your PCM has failed. If temperature reading is correct then coolant temp sensor is working and if both hi/low speed works when commanding it with scan tool that leaves PCM as only other option. Let me know how it goes or if you have more questions, thanks.

Customer: replied 1 year ago.

could the coolant temp sensor be malfuntioning

I think it would be worth replacing before moving onto PCM but usually if temp sensor fails you would get inaccurate reading of engine temp. Let me know how it goes or if you have more questions, thanks.

Customer: replied 1 year ago.

ok. I replaced the temp sensor and still gets to 221 and starts boiling over. also I just remembered that the customer said they replaced the radiator because there was a bunch of junk in the neck. she brought it to me and it looks like someone poured dirt in the old radiator . so I took every hose and line off and flushed both ways until clear. still ne cooling fans come on on their own. also I just compared the ect with the iat sensor before I started it today and the ect reads 86deg and the iat reads 77 deg. shouldn't they be the same is it sat over night and before its started.

Did you get this worked out yet?

Customer: replied 1 year ago.

nope. I had to get some others done

OK. If it's boiling over at 221F, I'd have a block check tool on the radiator, seeing if there are exhaust gases in the cooling system. I suspect that you have a leaking head gasket that is causing the cooling system to overpressurize. I would, at the very least, be looking to eliminate this as a cause before doing anything else, particularly since you had a good amount of "gunk" in the cooling system.

If you don't have a block check tool, they're about $40 at the parts store, and a very useful tool.

Customer: replied 1 year ago.

ya I was going to do that but it don't make any sense why the fans wont come on

I have been trying to find the temperature chart in the GM service manual about what temp the fans engage, but cannot come up with it for this vehicle. I typically don't see them come on until about 225-230F on these engines, though. 220F is considered a normal operating temp.

If you let the engine heat up to 230 or 235F, does the fan come on then? What if you turn the AC on, does the fan engage then?

Customer: replied 1 year ago.

really? I figured about 220ish. I cant get it much over 117 without it pushing water back out. let me check the ac thing. I just tried the scan tool to do it and unplugged the ect sensor

Customer: replied 1 year ago.

ok they do come on with the ac

At 220F, it shouldn't be pushing coolant out, so you either have an over pressurized cooling system due to a head gasket issue, or you have a failed radiator cap that doesn't hold pressure at all. Block check is what I'd be doing right now.

If the fans come on with AC, then the fan circuits work. You're looking at the ECT reading on a scan tool, yes?

Customer: replied 1 year ago.

yes I am looking at the temp on my scanner. I have the cap off making sure the air is bled with my yellow burp funnel

OK. Do the block check and let me know what you come up with. We definitely see a lot of head gasket issues on these 60-degree V6 engines.

Customer: replied 1 year ago.

ok. I might do it tomorrow though.

That's fine, just update me here when you get to it, and we'll continue from there.

:)

Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4413
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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