Head gasket question/advice (05 Tahoe 4.8)

Hey all,
I need advice for the specific situation I’m in. This might be a bit long so I apologize for that.

I have a 2005 Tahoe with a 4.8 and 162k. I’ve had the truck for about 3 years but it was my mom’s before that since about 08. Anyway, before I owned it (around 2017 and about 120k) there was a problem with coolant in the oil and combustion chamber that my dad (a Honda mechanic) attributed to the Castech head issue. He was planning to sell the truck at that time so he used some sort of stop leak, which has held to this day.

I’m planning on pulling the motor to replace a RMS (don’t have access to a lift) and do a few other odds and ends and wanted to put a permanent fix on this issue. After looking I see my heads are 862s, and I pulled a valve cover and couldn’t find the Castech logo anywhere on the head. Upper valve train was pretty clean too. Based on the fact that I can’t see the Castech logo, I’m thinking these are non Castech heads. I’ve read about a lot of Castech head issues and have also never heard of that leading to coolant in the combustion chamber, just the oil. Both of these lead me to think it was likely a head gasket failure instead of a head, but I’m not sure.

While the engine is out I’d like to replace the head gaskets & intake gasket, as well as the RMS. My dad suggests though that at this point if I’m putting on head gaskets I should get the motor rebuilt. The truck runs great and doesn’t use much oil at all. I’m unsure.

Appreciate if you read all that. Any advice is appreciated. Does this sound like the Castech issue? What would you all do in this situation?

Thanks,

Cody

I would do a leak-down test to try to find where the coolant is going. If you need to remove the heads, may be a good idea to go ahead and replace the valve stem seals.

RMS = rear main seal?

If engine is out, I would probably just do a complete reseal: rear, front, oil pan and valley cover.

I don't think the Castech heads leaked into the chamber. If I remember correctly, the leaked at a head bolt hole into the oil. So if you were getting a chamber leak it is either a cracked head or gasket. So if you dive into this, you may find you need to do heads anyway if it is like a crack around a valve.

strutaeng said:

I would do a leak-down test to try to find where the coolant is going. If you need to remove the heads, may be a good idea to go ahead and replace the valve stem seals.

RMS = rear main seal?

If engine is out, I would probably just do a complete reseal: rear, front, oil pan and valley cover.

Click to expand...

Yes RMS is rear main seal. Oil pan has already been done, will probably do these as well. There’s no leaks right now, haven’t had to add coolant since I had it, so not sure if the leak down would work.

Mudsport96 said:

I don't think the Castech heads leaked into the chamber. If I remember correctly, the leaked at a head bolt hole into the oil. So if you were getting a chamber leak it is either a cracked head or gasket. So if you dive into this, you may find you need to do heads anyway if it is like a crack around a valve.

Click to expand...

If I found I did need heads would you recommend a rebuild at that point?

cjmcglaughlin said:

If I found I did need heads would you recommend a rebuild at that point?

Click to expand...

Me personally, would go to the junkyard and pull a set of 706/862 heads and put them on my tahoe and go. But, I don't know your mechanical aptitude and don't know if that is something in your wheel house.
But also, if you have not had to add coolant in your time of ownership, I wouldn't mess with it. Find some heads for a possible future replacement, and set them aside. And just drive the thing.

The engine has 162k on it. It aint even broken in yet, to LS standards. That engine will get 300k easily, all you gotta do is change the oil and not rap it out like its a race car all the time. If it aint broke, dont fix it. Id just drop the tranny if all you gotta do down on the bottom is the RMS.

I second the idea of leaving the top side of the motor alone for now if you’re not having issues.

I also second the suggestion of dropping the transmission instead of pulling the motor. Get yourself a set of good jack stands and access to a transmission jack and it can be done without a lift. My son and I swapped the transmission on his F-350 in our driveway with no issues.

Thanks for the advice everyone. I might look into dropping the trans instead but thought this would be difficult because of the transfer case. Forgot to mention this is a 4WD.

Probably a wash if it's a 4x4 to pull engine vs transmission for rear main seal.

Is this a daily driver? Can vehicle be down for some time?

I recently took some grimey 317 to my local machine shop I'd bought for $75 for an engine I'm building. They cleaned, inspected, milled them, did a valve job and replaced the stem seals for $350. They are basically like new now. It took like a week to do the work.

I think they will go on my 06 Suburban LQ4 engine though. I've got what I suspect is an intermittent sticking lifter. I did the rear main seal and oil pan last year (dropped the transmission: 4L80e 2wd FWIW). I'm thinking replacing lifters, cam, front main cover and installing these heads. Engine has 260k and oil pressure seems good and runs strong, so I see no reason to pull it and mess with more than I need to.