Well after losing coolant for a while ,it finally showed in the oil filter today. The tsb I found on a search here, 06-06-01-019b does not list a NB 99 5.3 in it. Can my 5.3 have the Castech heads? These are the heads that can crack listed in the tsb. I have 187K on the motor, all original. Thanks for the help.

 

Before you condemn the heads, I would look at the intake manifold gaskets. Pressure test the system and see if coolant is leaking out the rear of the manifold or possibly the manifold itself is cracked. Much cheaper fix than heads.
If you must take the engine apart, try looking at the intake when dis-assembling. Check for signs of leaking at the manifold.

1999 Gmc Sierra 1500 Engine Intake Manifold - Delphi, Dorman - TheAutoPartsShop - TheAutoPartsShop

1999 Gmc Sierra 1500 Intake Manifold Gasket Set - Dorman, Fel-Pro - TheAutoPartsShop - TheAutoPartsShop

 

Thanks for the response. From what I've read and was told this intake does not have coolant at the rear but after looking thru the list of "common problems" some one mentioned the intake. The compression test of the cylinders were good. After some more research, I found out the castech heads were installed on the 2001 and up trucks. I'm tearing into it today to see what shows up. Anyone else have their intake leak coolant in the oil?

 

I just did intake gaskets on my dads 5.7L vortec, and it was leaking externally. Still had the OEM gaskets and RTV. It was leaking in the corner of the head and the intake where the RTV goes.

 

The 5.3 intake does not sit on the block like the older engines, they have a valley cover.

 

i had a similar issue but it turns up my waterpump was leaking out the weep hole causing me to loose my coolant,check into that before you go all out man just my 2cents -pat

 

I had those dreaded castech heads. Sure enough they were cracked and at 70k miles. If your getting coolant in your oil then it cant be a water pump issue. Cracked head, head gasket, intake gasket, thats it.