Hey guys, first post here. Just completed a LS gen3 5.3 swap in my 92 sonoma.

I'll try and keep it simple and get straight to it.

Here is a quick rundown. 01 GEN3 5.3 from a Silverado. Unknown KMS. Bought from a yard that deals with LS motors exclusively. Was told it had great compression. Told it had 220,xxx kilometers.

I did some maintenance on it while it was on the stand and cleaned it up. On top of non related to issue maintenance, New waterpump, stock T-STAT, upper and lower hose, superior v8 rad that was pressure tested prior to install, steam tube ran straight to rad. New rad cap, lower fed overflow tank.

Runs good, no smoke/ coolant out of exhaust. Does not overheat, fans kick on and off. Oil is good and clean,good pressure too, coolant is good and clean. filled and burped properly.

The issue I'm having is I'm getting pretty consistant Trace of bubbles out of my overflow. Thought it needed a new rad cap, replaced and it's still doing it. left rad cap off while running, and I can see the bubbles in the rad too. It's not foaming, and it's not boiling bubbles. Just air bubbles. If I top up my rad to the top of fill neck, keeping my overflow on the min line, when it runs and warms up, it will start releasing the air bubbles, and dumps about a quart of coolant into overflow, it will continue to bubble, but not dump anymore coolants after that, unless I top it back up. Then it will dump the same amount out into overflow again, the bubbling does not go away. It is always there. But it's not dumping all my coolant, and temps seem to stay fine. I've seen head gaskets go, but usually with overheating, coolant/oil mix or coolant loss. I dont have any issues like that, and I'm not really losing the coolant, it just evacuates a quart into my overflow, obviously to make room for the air, the air in the top of the rad, isn't allowing the coolant to return as it should. The rad builds pressure, and holds pressure. Top hose is firm and hot. Once cooled and I crack the rad, there is no more pressure in the system, but my rad is low, and I dont think there is any coolant in my upper hose.

Is there anything I should do prior to taking the heads off? Which I regret not doing while it was out and half apart? Am i missing something? You're help is greatly appreciated.

I'm not a mechanic, but have no problems doing the work. This is my first LS swap.

heads are 862 heads BTW.

 

Sounds like a headgasket. I believe there's a test to examine exhaust in your coolant. I'm not sure of the cost of the test but a new set of GM head gaskets for your 5.3 is $50 bucks from summit so I'm not sure it's even worth it. I'd swap them and be done with it.

 

thanks swapstang! I'm leaning towards it being a early sign of head gasket failure. Just odd that I dont exhibit any other symptoms, especially overheating if its exhaust gases entering the cooling system, or coolant entering the combustion chamber. I have just borrowed the block tester to sniff the coolant (liquid tester that changes color) and see if it is in fact exhaust gas creating the issue.

 

I had a "low mileage" 5.3 do the exact same thing to me. None of the classic signs. I just swapped the headgaskets and it was fine after that. I had a Powerstroke 6.0 which are known for exhaust in the coolant so that was my first thought to just do the headgaskets. They're cheap enough. Good luck.

 

Yea, I'm going to go home and test the resovior and see if it is, and pull the heads and replace if I have to. Seems like a real solid runner otherwise. Hoping I dont have to send heads out since it is not overheating. If I dont see anything stand out with the gaskets, i may send the heads out to be checked. Really kicking myself that i didn't do the HG's when I had the motor out. Guess I went off their word and did the "if it ain't broke, dont fix it" scenario.

Being new to LS motors, is there a preferable brand gasket to use? I've seen vague comments about felpro being a no no on these. Is there some specific brand to buy? Mahle? AC Delco?

Thanks for your info on my issue. Really appreciate it.

 

Go on summit and find the LS1/LS6 head gaskets. I believe it's part # 12498544. I've used them a few times and never had a problem with them. $50 for the pair you really can't go wrong.

 

Before pulling the heads, I would certainly want to do some more troubleshooting. Head gaskets are not a small job, and I would make sure that you actually needed one!

Do a compression test and also do a leak down test. Both are straightforward and will give you more clues as to whether it is a head gasket issue or something else.

Andrew

 

Thanks, Andrew.

I'm going to go home, and try this combustion leak tester and see if it shows any signs of exhaust in the coolant. I'm sure that would be a tell tale sign that there is a leak in one of the cylinder heads to one of water jackets.

The motor runs very good, and puts down some decent power. no issues other than the air bubbles. I will try and see if I can get my hands on a compression tester and check as well. Thanks!

 

Thanks for the part number!

 

I had a 04 5.3 with 90,000 miles puke a head gasket. Warming the truck up I glanced at the oil pressure gauge and it had like 5 lbs. drained the oil and there was at least a gallon of water in it. Not a good day.

 

That sucks!


I did just test the coolant resovior with the dye tester, and it definatley changed to a yellowish color. So I'm leaning towards a small leak between cylinder and water jacket. Think I'm going to pull the heads off from here and see. It doesnt look too terrible to get in there, and already had everything off once.

Going to try and get them off in the next day or two.

Thanks guys.

 

update

 

Well....that seems pretty obvious! At least you are on the right track to getting it fixed up.

Andrew