Where to start on coolant loss on a 03 LS MOTOR

[Bonestock3ott]

I have an 03. 5.3 liter in a GMC SIERRA that is using/losing coolant. No external leak, not mixing in oil. We have only had truck for about 8 months , unsure of mileage on motor. Where do I start to access if this motor is worth putting money into repairing or if a replacement engine is needed? Thanks

[406flyfish]

I think that was the years they had bad head castings. You wouldn’t notice it in the oil but that’s where it was going. Under the valve cover was a battery looking casting identifying the bad casting . Google it, there’s a bunch of info about it.

[88Ironduke]

Pull the spark plugs and look for one that's super clean. That's a good cylinder to start with.

[Killer Bee]

here's a couple of my older posts on the subject..

please not the gm tsb embedded in one of them..

both heads on my 02 were cracked, good luck!

http://67-72chevytrucks.com/vboard/s...98&postcount=4

http://67-72chevytrucks.com/vboard/s...4&postcount=13

[orngsikL]

weep hole on the water pump? look on the bottom side of water pump for snail trail of coolant.

bad heads were the castech heads. battery logo by the springs.

[homemade87]

If you have the 706 casting head there is a good chance this is your problem if you cant see coolant anywhere else . I had one fail . Easy to check . Remove both valve covers and inspect . It will be very noticeable which side it is when it comes off .

[Bonestock3ott]

Thanks for all the responses, does anyone have an opinion on best way to evaluate motor to see if it is worth putting the parts and time into repairing? if it is a cracked head (great possibility) it looks like the parts needed:
heads
gasket set
head bolts
intake bolts?
oil pump? I've heard as LS motors wear, oil pressure becomes an issue
fluids
The Chassis is a really clean truck, unfortunately I do not know any specifics on how many miles are on the drivetrain. Might be better off finding a donor vehicle with less/known mileage that the chemicals our DPW dumps on our roadways here in Western NY tend to make not road worthy before the drivetrain is shot.

[homemade87]

Originally Posted by Bonestock3ott

Thanks for all the responses, does anyone have an opinion on best way to evaluate motor to see if it is worth putting the parts and time into repairing? if it is a cracked head (great possibility) it looks like the parts needed:
heads
gasket set
head bolts
intake bolts?
oil pump? I've heard as LS motors wear, oil pressure becomes an issue
fluids
The Chassis is a really clean truck, unfortunately I do not know any specifics on how many miles are on the drivetrain. Might be better off finding a donor vehicle with less/known mileage that the chemicals our DPW dumps on our roadways here in Western NY tend to make not road worthy before the drivetrain is shot.

If it were mine , if this was the case I would just piece it together . Just see what side is the problem and replace that head . I would not worry about the oil pump . I have never seen myself a oil pump on a ls fail , even on high mileage . Its usually the pick up oring that's a problem . If you are not having a problem I would leave it alone . If needed just run a little heavier oil .

There is another head that is identical to the 706 . It is a 862 i believe . Just different foundry . These heads will be pretty cheep . Just have it checked at a machine shop . Also intake bolts are reused .

On the other hand there is another forum member here that had your same problem . He put in a product that GM has in the coolant and has been quite successful for a couple years now . It was high millage as well and sealed the leak . For an engine you are going the pull out and discard this may be worth a try .