You are on to something there, with the radiators. Struggled with the hot, AC off bs for a while. I made a number of cooling system improvements at the same time, so it took a while to figure it out. But I think I have it solved on my machine. Source of the problem: Aftermarket radiator, with no flow restriction orifice in the small radiator hose connection, that goes to the surge tank. Coolant was flowing at a good rate from that top fitting into the surge tank, and if you look at the cooling flow circuit, this flow bypasses the thermostat. So it is essentially the same as having your thermostat half open all the time. I put a restriction in the hose, and have not seen the issue since then. Now why the "too smart for it's own good" ECM software is also programmed to interpret this slower than expected engine warm up rate as an overheat condition, is anyone's guess.
07 Tahoe engine hot ac turned off
- Thread starter Dukenukemx
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adventurenali92
Full Access Member
This is correct. I just went through this scenario in replacing the radiator on my 2006 as well. I had read several threads where guys had replaced the radiator and the truck would not get up to operating temperatures. The “engine hot” but is new information. But they couldn’t figure out why the truck was not getting up to operating temp. And as you stated on the OEM radiator there is a small restriction piece in the top line that routes coolant to the surge tank. I was seriously concerned about how to resolve this if my new radiator didn’t have the correct piece installed. I lucked out and the aftermarket radiator I got from 1800radiator.com had the correct restrictor in place.
Edit: hard to see in the photo but that little restriction almost looks like a little washer installed inside the piping that connects to the surge tank line:
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Tozan
Overlander
Great I will check that out. That certainly sounds plausible If needed I could add an insert into the hose..
You can also just use a small hose clamp and squeeze the hose down a bit to restrict flow as well and see what happens.
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Dukenukemx
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I think the problem has been solved as I changed the temp sensor again, with a new thermostat again, and flushed the coolant... again. So far nothing wrong.
Tozan
Overlander
I used a C-clamp on the hose to restrict it, so far it seems to be working. So my next step is to determine how large of a hole in the restriction will be needed. Can anyone measure the ID of the stock fitting?
What is the main reason for this hose does it just need to vent air out of the radiator?
Tozan
Overlander
So far the clamp idea is working great it has not happened since restricting the water flow in the top tank hose.
kbuskill
***CAUTION*** I do my own stunts!
Just had this happen to me this evening... driving home from church and the "Engine Hot, A/C Turned Off" message came on and the temperature gauge was sitting at the bottom (160°) but the OBD2 data was showing 142°. The truck was clearly not overheating and the coolant level was fine.
I just swapped to the Cold Case radiator last Saturday. Looks like I will be figuring out a restrictor for the upper surge tank hose.
kbuskill
***CAUTION*** I do my own stunts!
I think I am going to have a closer look at the old radiator and see what size hole it has up inside the radiator and then figure out which route I want to take.
I thought about having a buddy of mine tig weld an aluminum "washer" over the nipple.
It wouldn't need to be welded all the way around, just tacked in place, because the hose would slip over it and be clamped.
I will probably figure out something easier though.
A ball valve in line would be adjustable.
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