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This one's got me stumped. Runs too cool. Solved

Massey

Full Member
Joined
Jan 11, 2009
Messages
161
Location
Tacoma, WA
Hey guys! OK this one has me stumped pretty good. Here is what's up. 2004 Avalanche with 377K on the clock. Yesterday the radiator blew up on me while on the freeway. The temp got a bit over 210 when I finally found a safe place to pull over and get a tow. It didn't run bad or anything, I just got antifreeze sprayed all over my windshield and all down the left side of the truck. Blew right at the tank seam... pretty typical.

Got new rads... Got 2 gallons of DexCool concentrate, and went to work. Lower heater hose with the Y in it broke as I was taking things apart... Great more $$$ out of my pocket. I had green AF in the truck so I flushed it all out till water came out clear, no more green. Everything went together perfectly, no issues. I started the truck after the overflow was full and topped it off after it sucked some down. The engine only got to about 150° idling. OK so off to a test drive and I then got to a whopping 158°. Temps were verified by an Autel scanner and the gauge also was showing really low. So I figured that my T-stat was bad and my slight overheat may have killed it open. Today new T-stat (187°), more new coolant (can capture it, cant recover it... GRRR more $$$). Now it gets to about 174° again verified by the scan tool. I also replaced the sensor on the left head, same business with the temps. Gauge in the dash used to show just below 210°, just like every LS engine I have ever owned. I drove 60+ miles home tonight and the temps stayed steady. I get heat, but not cook you out of the truck heat that I had just yesterday before it blew. Water pump is newer and nothing is leaking anywhere. No coolant smell in the exhaust, no steam from the exhaust after the truck gets luke warm. I do not have a IR temp scanner at the moment, I need to get new batteries so I couldn't say what the block or radiator temp are. Nothing feels insanely hot, and I can hold onto the hoses without being uncomfortable.

Old T-stay was OEM or at least an AC Delco unit, and it was not stuck open this morning. I could move it open easily as well. The seal did look horrible, and left black on my hands when I touched it, so good call on the replacement anyway. Yes I do see flow in my overflow, I get the small upper hose squirting coolant back into the overflow and when looking in the filler you can see the coolant circulating. Oh and the radiator was OEM as well. It lived a good long life!

Any clue as to my issue? My truck is a engine powered fan type, and my fan clutch seems to be working well. Engine runs well, no loss or gain of power, just normal running.
 
There was a member a while back that chased an overheating issue, not a low temp issue.

He described changing all the normal suspects and went to great lengths to make sure his coolant fill was proper several times.

What reminded me of his situation was your description of seeing coolant "flowing" in the surge tank.

While on both of my trucks, with the surge tank cap off, I can see some slight movement of coolant, but not what I would call a flow.

I can get a squirt of coolant into the tank if I mash the upper radiator hose.

What ultimately was found to be the problem for the other member was on his new radiator, at the port where the smaller rubber hose goes to the surge tank, the size of the inner hole inside the port on the new radiator was too large.

When comparing the size of the internal opening to his original radiator, he found the port on the original radiator was a much smaller opening.

It can be assumed that the smaller opening was metering the flow of coolant toward the surge tank as it came out of the radiator toward the tank.

If I recall correctly, he was observing a "flow" of coolant in the tank.

I had never heard of such a thing before.

In his situation, the full sized hole in the port was allowing coolant to rush through the surge tank much faster than designed and for some reason, it was allowing the coolant to get too hot in his case, even though everything else was proper.

This may not be the same with yours, but a quick test would be to pull the hose off of the radiator and shine a flashlight up into the port to see what going on there.

Can't hurt.

And as a reference, on both my 2003 Avalanche and 2004 EXT, when comparing the cluster temp gauge with my scanner's live data, from a cold start, the larger hash mark between the 160 and 210 is the point of my 187 degree thermostat opening up.

The temperature will continue to rise until the needle is just to the left of the 210 hash mark.

The normal operating temp of both of my trucks rides between 195 and 205 according to the live data with the needle never going above the 210 hash mark.

I have a severe duty fan clutch installed on both of my trucks and it is extremely rare to see my engine temperature ever cross the 210 mark.
 
I agree that the half way mark is about 187 ish as that’s where the needle gets to when it reaches what is now it’s max temp. The flow I witnessed I have noticed in all LS trucks I have ever owned, and on any I have replaced a water pump or radiator on. This one simply has me bugged.
 
Hey Massey
Good to see you back
Got me stumped too. Heater core flushed well?
I managed to load the core with CLR and sit for a while before flushing.
Did you put in concentrate or 50/50 Dexcool? Should be 50/50
 
I Say get another water temp gage cand put a tee in the heater hoses and then insert this new temp gage to compare.

Who knows what you have is accurate?
 
So the flush went really well, the water flowed easily through the heater core. I made the water enter the engine through the core, then out the water pump.

my antifreeze is a little on the strong side right now, but when it was first filled it was pretty close to 50/50 maybe a bit on the weak side as I know there was still some fresh water in the block before filling 2 gallons of AF and 2 gallons of water. After I replaced the T-stat I filled 2 gallons of AF and one gallon of water. Then I added about bit more than a quart after the temp sensor got replaced. I know 50/50 is the perfect ratio, but I doubt this is the issue as I get higher temps now than I did when it was closer to 50/50… not much higher, but higher.
 
So for those curious to the resolution of this issue, I finally have one!

Defective brand new radiator.

So there is a small 7/16th inch hose at the top right of the radiator. Well there is supposed to be a hole that is only 1/16” or so in diameter in this location feeding this 7/16” hose. When I checked my friends 5.3L he didn’t have any coolant flow in this area, I clearly did. So I tried kinking that hose and removing the flow. And wouldn’t ya know, I got temps back to the 210 point… right where they are supposed to be. So I investigated the situation a bit more. Went to the parts house I bought the new rad from and looked at one they had… the hole was the same size all the way into the tank. I still had access to my old one so I busted the tank open and found that fitting was fed by a 1/16th“ hole. So while I do need another new radiator, I’m not too interested in replacing this one quite yet, it’s below freezing here the last few weeks and if all I need to do is create a restriction I can do that.

My fix,
I bought a set of brake bleeder screws that had a hole of about the same diameter as the factory tank, took them home and ground off the tip so the hole is exposed, then I ground the hex part down to a round shoulder so it wouldn’t go too deep into the tank fitting. After all that I screwed it into the tank fitting and returned the hose. The truck heats up perfectly now with no issues.
 
SO where is the other end of this hose connected into coolant system?
Over Flow Tank?
 
SO where is the other end of this hose connected into coolant system?
Over Flow Tank?

Yes.

This is the port on the upper right tank of the radiator that connects directly to the coolant surge tank.

With this happening as I described further up in the thread and also to Massey, it looks like this may be a more widespread issue than we thought and others that may be experiencing similar issues may need to be made aware of the possibility.

I know for me, I will check on the size of that inner hole in that port before I install any replacement radiators in my trucks.

Good on Massey finding his issue and developing a workable plan.

:) (y)
 
So for those curious to the resolution of this issue, I finally have one!

Defective brand new radiator.

So there is a small 7/16th inch hose at the top right of the radiator. Well there is supposed to be a hole that is only 1/16” or so in diameter in this location feeding this 7/16” hose. When I checked my friends 5.3L he didn’t have any coolant flow in this area, I clearly did. So I tried kinking that hose and removing the flow. And wouldn’t ya know, I got temps back to the 210 point… right where they are supposed to be. So I investigated the situation a bit more. Went to the parts house I bought the new rad from and looked at one they had… the hole was the same size all the way into the tank. I still had access to my old one so I busted the tank open and found that fitting was fed by a 1/16th“ hole. So while I do need another new radiator, I’m not too interested in replacing this one quite yet, it’s below freezing here the last few weeks and if all I need to do is create a restriction I can do that.

My fix,
I bought a set of brake bleeder screws that had a hole of about the same diameter as the factory tank, took them home and ground off the tip so the hole is exposed, then I ground the hex part down to a round shoulder so it wouldn’t go too deep into the tank fitting. After all that I screwed it into the tank fitting and returned the hose. The truck heats up perfectly now with no ishey having same problem so you happen to know the size of the brake bleeder screw
 
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