2003 Tahoe coolant system leak or head gasket leak?

[tRidiot]

Sounds just like the Castech head failure I experienced. I drove mine slowly SLOWLY losing coolant for probably 4 or 5 years. Only way to know for sure until you blow out a head is to pull the valve cover and look for a clean area around that cylinder - I think it's #5?

Do you have the 706 heads?

Pull it out, rebuild it, get another 200-300k out of it. You'll be happy with the peace of mind - especially with the price of used or new vehicles these days!

 

[tomloans]

Sounds just like the Castech head failure I experienced. I drove mine slowly SLOWLY losing coolant for probably 4 or 5 years. Only way to know for sure until you blow out a head is to pull the valve cover and look for a clean area around that cylinder - I think it's #5?

Do you have the 706 heads?

Pull it out, rebuild it, get another 200-300k out of it. You'll be happy with the peace of mind - especially with the price of used or new vehicles these days!

I am definitely going to replace both sides. This job is new to me so I am not sure what cylinder heads I have. 2003 tahoe LT is what I have. I just want to replace it with the same heads. Will read up and watch a few videos to wrap my head around the job and parts list. But first I need to confirm the problem.

 

[tRidiot]

Actually, if it's the 706, you DON'T want the same heads. The 706 heads have a casting defect found in a large number that allows leaking of coolant slowly into one cylinder - I believe it's #5.

Here's how you can tell -

Actually, from my research, both the 706 heads AND the 862 heads were prone to this problem. Once you get the head open, you can see the casting mark inside, if it looks like a battery, like this:

then you know you are hosed - those are 706 heads made by Castech. If they look like the square swirl in the first picture or something else, then they weren't made by Castec. Of note, those Castech 243 heads in this pic would not be affected by the problem - it is supposedly only the Castech 706 or 862, NOT the 706 or 862 made by other manufacturers. Go figure.

The problem I ran into trying to find another set of 706/862 heads was that I could not get anyone selling any (online) to tell me if they had the Castech battery casting mark inside. Of course, I was not willing to spend money on a set of used heads and have them shipped in, just to learn they were the same thing I was replacing. It was a major PITA.

I believe a set of 243 heads like those above would work, but you'd need to do some research yourself on which heads will work as a swap-in with your motor, intake, all those things. I won't pretend I'm well versed in those things, and eventually I gave up and just ordered a rebuilt LQ9 6.0L to replace my L59 5.3L. It is a direct swap with almost everything bolting on directly - even my FlexFuel intake, fuel rails, everything. I did upgrade to the same water pump used in the 2500 Surburban, I'm not sure if it's the same as my 5.3L had.

I wish you luck, but if I were you I would NOT get a set of 706/862 heads without verifying first that they are not Castech-made.

 

[dougo]

A few years ago I had a civic that was losing coolant , I did the exhaust gas test no issue , Pressure test no issue , no smell at tail pipe ,compression test no issue , Pull the head no issue , new hoses , still losing coolant on a hot day my Kid was driving on the highway when she got home I meet her outside I could smell it and hear it if i got close to the radiator but only for a short time , I let the car cool pressure test again exceeded pressure no leak replace the Radiator and drove another 50k no issues I think their was a pin hole on top of the rad under the cross member that would only leak when the car was HOT.

 

[mattbta]

Even if you don't have milkshake under the valve covers, Get some UV dye and a light, cycle that into the cooling system. Pop the valve covers and look for highlighted liquid while under pressure - BTW, IIRC 15 PSI is max recommended pressure. I had slow coolant loss for several years, but also saw it coming from the water pump weep hole. I ended up losing more rapidly, so replaced the water pump. Was still losing rapidly and saw white smoke on startup out of the exhaust. Had to get refurb'd heads and put on. Unfortunately, one of the refurbs cracked in less than 500 miles. The vendor honored their warranty, but it wasn't an easy process so I can't wholeheartedly recommend them. (I ordered more 706's because I'd read they flow better than 862 stock for stock and ended up with one castech in the pair...the one that cracked was castech.) Dye was maybe $8 on Amazon? General Motors 89022219 ACDelco 10-5046 Dex-Cool Leak Detection Tracer Dye - 1 oz

Here's what I saw on one of the refurbished heads. They were pristine prior to install:

UV Dye

In the sun

Good luck.

 

[dougo]

Even if you don't have milkshake under the valve covers, Get some UV dye and a light, cycle that into the cooling system. Pop the valve covers and look for highlighted liquid while under pressure - BTW, IIRC 15 PSI is max recommended pressure. I had slow coolant loss for several years, but also saw it coming from the water pump weep hole. I ended up losing more rapidly, so replaced the water pump. Was still losing rapidly and saw white smoke on startup out of the exhaust. Had to get refurb'd heads and put on. Unfortunately, one of the refurbs cracked in less than 500 miles. The vendor honored their warranty, but it wasn't an easy process so I can't wholeheartedly recommend them. (I ordered more 706's because I'd read they flow better than 862 stock for stock and ended up with one castech in the pair...the one that cracked was castech.) Dye was maybe $8 on Amazon? General Motors 89022219 ACDelco 10-5046 Dex-Cool Leak Detection Tracer Dye - 1 oz

Here's what I saw on one of the refurbished heads. They were pristine prior to install:

UV Dye
View attachment 362598

In the sun
View attachment 362599

Good luck.

Wow great info Thanks for posting

 

[tomloans]

Actually, if it's the 706, you DON'T want the same heads. The 706 heads have a casting defect found in a large number that allows leaking of coolant slowly into one cylinder - I believe it's #5.

Here's how you can tell -


View attachment 362578

Actually, from my research, both the 706 heads AND the 862 heads were prone to this problem. Once you get the head open, you can see the casting mark inside, if it looks like a battery, like this:

View attachment 362579

then you know you are hosed - those are 706 heads made by Castech. If they look like the square swirl in the first picture or something else, then they weren't made by Castec. Of note, those Castech 243 heads in this pic would not be affected by the problem - it is supposedly only the Castech 706 or 862, NOT the 706 or 862 made by other manufacturers. Go figure.

The problem I ran into trying to find another set of 706/862 heads was that I could not get anyone selling any (online) to tell me if they had the Castech battery casting mark inside. Of course, I was not willing to spend money on a set of used heads and have them shipped in, just to learn they were the same thing I was replacing. It was a major PITA.

I believe a set of 243 heads like those above would work, but you'd need to do some research yourself on which heads will work as a swap-in with your motor, intake, all those things. I won't pretend I'm well versed in those things, and eventually I gave up and just ordered a rebuilt LQ9 6.0L to replace my L59 5.3L. It is a direct swap with almost everything bolting on directly - even my FlexFuel intake, fuel rails, everything. I did upgrade to the same water pump used in the 2500 Surburban, I'm not sure if it's the same as my 5.3L had.

I wish you luck, but if I were you I would NOT get a set of 706/862 heads without verifying first that they are not Castech-made.

Thank you for this write up! It rarely is easy is it? Thanks again this is a good starting point for me.

 

[tomloans]

Wow great info Thanks for posting

Thanks for the write up. This is enlightening to say the least. Now somehow, I have to find just the kind of Cylinder head.

 

[tomloans]

A few years ago I had a civic that was losing coolant , I did the exhaust gas test no issue , Pressure test no issue , no smell at tail pipe ,compression test no issue , Pull the head no issue , new hoses , still losing coolant on a hot day my Kid was driving on the highway when she got home I meet her outside I could smell it and hear it if i got close to the radiator but only for a short time , I let the car cool pressure test again exceeded pressure no leak replace the Radiator and drove another 50k no issues I think their was a pin hole on top of the rad under the cross member that would only leak when the car was HOT.

I just changed my entire system including the radiator. It didn't make a difference. I am going to pull the drivers side valve cover and see if number five has coolant around it and send my oil in for analysis.

 

[dougo]

I just changed my entire system including the radiator. It didn't make a difference. I am going to pull the drivers side valve cover and see if number five has coolant around it and send my oil in for analysis.

I have seen some were on this forum were GM has bulletin that suggests using some tablets in cases like this have you seen that bulletin

 

[tomloans]

I have seen some were on this forum were GM has bulletin that suggests using some tablets in cases like this have you seen that bulletin

Not sure I want to do this for a head crack. I want to get to the bottom of it first. Thank you though never heard of this bulletin until now. Looked it up and it is real for pin holes leaks I believe.

 

[tomloans]

Just did some cursory searches. This rebuild has the correct symbol ( not the battery symbol ). What do you guys think?

https://www.autozone.com/external-engine/engine-cylinder-head/p/nutech-engine-cylinder-head-2ct7/992894_0_0

 

[BarryvG]

I had a 2001 Z71, 5.3L that had the same problem, and the dealer couldn't figure it out, either, until we literally BOTH were on a message board at the same time. It WAS a cracked/defective head. Was slowly leaking coolant, and there was a weird sound, but I had it looked at by a local mechanic, as well. He thought it might be some "O-ring" in the oil pickup, which didn't make sense to me, so I finally took it to the GM dealer on the mainland.

GM new about it, but refused to acknowledge it as a recall, as it didn't fall under safety guidelines for operation. I didn't have the know-how to replace it myself, so had them replace both at a cost, if I can remember, of about $1800, total, possibly more. It was a while ago. Pretty $hitty of GM to not deal with it. Not sure how MANY 5.3s were effected, but I don't think it was widespread. A few on here have mentioned one brand, so they must know...

 

[tomloans]

Thank you and this board is so encouraging and helpful. Two things first. Drivers side valve cover is coming off for a visual inspection and oil sample will be sent out as well unless visual exam is obvious.

 

[tRidiot]

Just did some cursory searches. This rebuild has the correct symbol ( not the battery symbol ). What do you guys think?

https://www.autozone.com/external-engine/engine-cylinder-head/p/nutech-engine-cylinder-head-2ct7/992894_0_0

Yes this would work, if you have the know-how and ability to replace the heads. That is for a single, right? I would replace both at the same time, personally - and all the other things that go with it. It turns into a full top-half rebuild, essentially.

The problem with this is that then you have a new, tight top half, and the bottom is still the old, worn bottom half. I was advised by numerous people - if you're going to rebuild the top half, rebuild the whole thing, or in a few months, you'll be doing the bottom too.

I don't know how true that is - it does depend on how many miles you've got on it, how good the lower half is, etc. It's up to you and your budget - you could do a top half yourself for maybe ~$1000-1200? That's with those $600 pair of heads and a total guess on my part. You can spend as much as you want on components - cheap out, or upgrade little by little. I dunno.

Certainly if you're mechanically handy, I think you could do this. If I knew then what I know now, I might have done the top half rebuilt myself before the thing blew up on me. YouTube videos make it clear how NOT difficult it is to pull the heads on these motors, and the rest is simply picking out parts and dropping them in. I don't want to say it's foolproof, but it isn't rocket surgery, either. The problem I ran into was - well, if you're gonna do this, you oughtta do this, this, this and this while you're in there.

Mine ended up costing me about $8500 when it was all said and done, but I have a newly-rebuilt transmission and LQ9 6.0L that should last me a couple hundred thousand miles. Now I just need to replace everything else around those things. lol

 

[tomloans]

Yes this would work, if you have the know-how and ability to replace the heads. That is for a single, right? I would replace both at the same time, personally - and all the other things that go with it. It turns into a full top-half rebuild, essentially.

The problem with this is that then you have a new, tight top half, and the bottom is still the old, worn bottom half. I was advised by numerous people - if you're going to rebuild the top half, rebuild the whole thing, or in a few months, you'll be doing the bottom too.

I don't know how true that is - it does depend on how many miles you've got on it, how good the lower half is, etc. It's up to you and your budget - you could do a top half yourself for maybe ~$1000-1200? That's with those $600 pair of heads and a total guess on my part. You can spend as much as you want on components - cheap out, or upgrade little by little. I dunno.

Certainly if you're mechanically handy, I think you could do this. If I knew then what I know now, I might have done the top half rebuilt myself before the thing blew up on me. YouTube videos make it clear how NOT difficult it is to pull the heads on these motors, and the rest is simply picking out parts and dropping them in. I don't want to say it's foolproof, but it isn't rocket surgery, either. The problem I ran into was - well, if you're gonna do this, you oughtta do this, this, this and this while you're in there.

Mine ended up costing me about $8500 when it was all said and done, but I have a newly-rebuilt transmission and LQ9 6.0L that should last me a couple hundred thousand miles. Now I just need to replace everything else around those things. lol

Thanks. I have done some very extensive jobs on all my vehicles. So I am pretty well mechanically inclined. I think. The hardest part on this seems to me unbolting the exhaust from the manifold. really. LOL Sounds silly but that has always been tough for me on these vehicles. Going to spray it down way in advance. Other than that, the sequence of getting this done seems pretty straight forward. It will likely take me longer than others because I go methodically and slowly. Videoing along the way as well. Not have heard about the engine failing because there are stronger areas but that makes sense. This vehicle has been lightly driven and gear and tyranny oiled front to back about 6 times in 200k miles. Zerk fittings have been greased every 20k hence the front end is like new. I just changed out the sway bar Bushings, end links, and bump stops as well but really they were still in respectable condition. Transmission is solid so far.

I am going to do the valley pan gasket, the oil sensor in the back, and the knock sensors while I am in there and trust my maintenance over the years will pay off.

But first I still haven't confirmed if I have a problem yet.

Nevertheless I have started a parts list over at Rockauto and so far I have about $1200 in parts for a complete job including the extras I mentioned.

I want it done right and am afraid to give it to another mechanic.

Just recently I replaced the fuel pump in it and there was grunt work work done on this by the mechanic who put in the last fuel pump. Gouging the mating surface where the lock ring turns on. Had to cut and shave it down in order to slide the ring back on. Couldn't understand why anyone would have to gouge the surface to remove that ring. Anyways I don't have trust in these mechanics in my neighborhood so I have to do this myself. I know I am not going to force something or gouge something then hide it or ignore it. I think if I knew a really good mechanic I might have them do it. But I am the best mechanic I know at the moment. LOL

 

[SnowDrifter]

I want it done right and am afraid to give it to another mechanic.

Just recently I replaced the fuel pump in it and there was grunt work work done on this by the mechanic who put in the last fuel pump. Gouging the mating surface where the lock ring turns on. Had to cut and shave it down in order to slide the ring back on. Couldn't understand why anyone would have to gouge the surface to remove that ring. Anyways I don't have trust in these mechanics in my neighborhood so I have to do this myself. I know I am not going to force something or gouge something then hide it or ignore it. I think if I knew a really good mechanic I might have them do it. But I am the best mechanic I know at the moment. LOL

Hey you sound like you have my luck

Anyone touches it for any reason, and they ***** even the most basic of tasks

Only time I let someone else touch my rig was to do the fuel pump and they left it parked in a snowstorm with the windows down. Yay.


Just.... Be careful of the "while I'm in there" trap. It has merit, but you'll need to cut yourself off at some point.

Finish your diag, sort what you need. Hell.... It's also entirely possible there's nothing wrong with your engine and you have 2 separate issues at the same time being funny. Say.... For example... A leaky rear heater line that only does so when hot and under pressure, and a bad engine oil dipstick o-ring, causing rainwater to get in your oil and coolant loss. Can't say that's your issue. I'm just tossing out an example to say: step back and look at the whole problem, don't just search for what you want to find. The second you go 'tunnel vision,' you've lost the diag.

That said: If, *IF* you need heads and will be doing that work, what I would do:

- Compression and leakdown tests before you take the heads off. Get a base level motor health measurement. Check these wet and dry.
- Pop the oil pan off, remove the main bearing caps, and inspect. See how they look visually, then plasti-gauge them to check for tolerance. If they're good, don't mess with them. Leave the rest of the engine alone.
- Strictly speaking, you could hone and re-ring your cylinders if you determine that's needed. Just pop your pistons out, hone/descale bores, re-ring, set gaps, and you're good. But again... Only if needed.
- While you have the pan off, do the pickup tube o-ring.

Big difference in amount of work and parts if you're just replacing the heads vs. pulling the motor and doing a full rebuild. If all she needs is heads, don't go dumping an extra 2 dozen hours of labor and couple thousand into it.

 

[tomloans]

What's odd is that I only have about 3 months on an oil change and about 900 miles and it is very dirty. I drained enough today after sitting for about 36 hours into a clear glass to see maybe if water flowed out first. This wasn't the case so this is good. But the oil was very dark considering the amount of time and miles. Usually it is still very clear after only 900 miles. I am sending it into Blackstone today. I will keep you guys informed on what happens next.

 

[tomloans]

OK Major Update!

See Pics. I just replaced the valve cover 6 months ago and about 2300 miles ago and here is what it looks like. The gunk seems to have built up the cylinder head between the 5th and 3rd cylinder most ( dont have a picture of this )... Any conclusions?

 

[mattbta]

In my amateur opinion, that's definitely water/coolant mixed with oil. When my refurb head cracked, it looked like that as the oil was practically brand new. Get the dye and light and pressurize it and you might spot the leak. Otherwise, just prepare for swapping both heads, again, in my amateur opinion.

This is mine with unknown miles on the oil with the OEM heads.