Head gasket question/advice (05 Tahoe 4.8)

[cjmcglaughlin]

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

 

[strutaeng]

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.

 

[Mudsport96]

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.

 

[cjmcglaughlin]

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.

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.

 

[cjmcglaughlin]

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.

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

 

[Mudsport96]

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

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.

 

[rockola1971]

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.

 

[wjburken]

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.

 

[cjmcglaughlin]

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.

 

[strutaeng]

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.

 

[iamdub]

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

The Castech logo can't be seen unless you remove the rocker pedestal rail. Regardless, if the oil didn't have the telltale yellow/cream/milkshake stuff or black and sludgy (from the moisture being steamed out of it but other coolant chemicals remaining), then your coolant and oil aren't mixing. You have to be sure of what you're looking at, though. Ask your dad to clarify if coolant was, in fact, in the oil.

Castech or not, it could be a head or block with a defect and crack. Or a failed head gasket. Maybe the owner prior to your mom somehow ran it hot and warped the head slightly or the head gasket failed and it was such a small enough breach that the stop leak was able to patch it. GM has their own "stop leak" tablets for the cooling system that they've designated as a viable repair. As far as rebuilding at only 162K, I don't see why it'd need that if the oil didn't have water in it and if the oil pressure is good/stable. I've replaced Castech heads on a 182K-mile 5.3 that was so sludged up from coolant mixing that it clogged the pickup tube and lost oil pressure. It was brother's truck and it came to me with collapsed and clacking lifters. Surely had bearing wear, but no scoring. Thoroughly cleaned it out, slapped some used 799s on it as I received them from a FB Marketplace find, replaced the usuals with the only upgrade being a high volume oil pump (with stock pressure relief spring) and sent it. Almost 5 years and 50K miles later, it's still towing a trailer with 4-door RZR, dirt bikes and 4-wheelers to his camp three hours away and back.

If yours is or was just slowly burning off the coolant through a combustion chamber, then the engine's bearings and rings should be in great shape with another 160K+ miles left in it if it hasn't been beat on. I'd have the heads checked for cracks and cleaned (including a cleaning pass to resurface them) with new valve seals and lap in the valves. While they're off, closely inspect the block for cracks. Pay extra close attention to the head gasket when you disassemble it for evidence of failure and patching from the stop leak.

Or, as @rockola1971 and @wjburken suggested, if it ain't broke, don't fix it. The RMS job doesn't really have any connection with a head job. You can R/R the heads with the engine in the truck if you need to dive into that down the road. It's kind of a "do everything or just do what it needs" thing that you'd have to determine based on your resources and other goals (all new gaskets, if you're dead-set on cracking it open for the coolant thing along with the RMS job, etc.).

 

[Fless]

I agree with leaving it alone re the non-current coolant loss. There are various tests you can do, like dry and wet compression tests.

Also various mfrs. make a test kit that will test for combustion gasses in the coolant, like this from Lisle, if you want some peace of mind:

https://www.oreillyauto.com/detail/c/lisle/chemicals---fluids/leak-detectors---sealers/27fbee18b299/lisle-combustion-leak-detector/lis0/75500

 

[cjmcglaughlin]

It is a daily but I can borrow another vehicle if I needed to. Thinking for now I’m going to look into pulling the transmission instead. The cooling system seems happy for now and I really don’t want to mess with it, until a possible rebuild hopefully farther in the future.

 

[Eldiablo]

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

To low of miles. Pull the heads takem in and pressure check them clean it all up put back together , run it until 500 thousand!