2000 4.8 Coolant Leak Down Back Of Engine

akinz · March 8, 2010

I have read a few posts about head failure and head gasket failure but haven't came across any of the same symptoms I have. I have the intake taken down and realize that there is no coolant running through the intake manifold. The leak is coming from the back passenger side of the engine. I can notice the trail of coolant coming down between the tranny and the back of the engine. I can't pinpoint exactly where the leak is.

There is no sign of coolant in the oil, or oil changes either.

Any help or points in any direction would be greatly appreciated.

Thanks

Draenor · March 8, 2010

Just a bad casting in the heads.

desrtrat · March 8, 2010

i can't remember if the 5.3 has any freeze out plugs in the back, if so one may be leaking. there is also a previsions for a block heater also..

good luck

akinz · March 9, 2010

i can't remember if the 5.3 has any freeze out plugs in the back, if so one may be leaking. there is also a previsions for a block heater also..

good luck

It's the 4.8 actually. I've tried looking for the plugs but it's kind of hard to see. Would they be in the block or the head? I've proceeded to tear down to the heads and have the valve covers off. Just waiting to get some torches so I can remove the manifold to pull the heads.

After reading a few of these different posts, I can't think of anywhere else it could be coming from. I figured that I'm this far I might as well keep going.

I'll post back with pictures and updates as often as I can.

Thanks again for the replies

kgrigsby · March 9, 2010

I have read a few posts about head failure and head gasket failure but haven't came across any of the same symptoms I have. I have the intake taken down and realize that there is no coolant running through the intake manifold. The leak is coming from the back passenger side of the engine. I can notice the trail of coolant coming down between the tranny and the back of the engine. I can't pinpoint exactly where the leak is.

There is no sign of coolant in the oil, or oil changes either.

Any help or points in any direction would be greatly appreciated.

Thanks

This may give you a place to look before you tear down further

Last year my 1999 gmc 4.8l 250,000 km had all the issues with the valve noisy lifters, loss of coolant with no visible sign of leaks on outside of engine.

I checked to see if i had the castec heads and did not.

Another thing I found in regards determining if you have antifreeze in you oil is your oil will not always be ' milky' on the oil dipstick to confirm that antifreeze has mixed with the oil, antifreeze does not like to mix with oil. You have to drop your oil and if it comes out kind of chunky or blobs, you have antifreeze in the oil, it will end up on the bottom of your drain pan.

I found the problem when I pulled the intake manifold off, THE TOP ROW OF BOLTS ABOVE PUSHROD GALLERIES, (11mm, not the main head bolts) ON THE LEFT HEAD HAD LOST TORQUE and subseqently antifreeze was able enter the oil pan via the valve pushrod galleries, there was evidence of corrosion, etc on the pushrods, aft lifter area.

At this point I was 90% sure I found the leak but decided to change the head gaskets, when they were pulled I found no evidence of leakage around the head gaskets gaskets.

So what I suggest, pull your intake manifold off, (only way to get at the smaller 11mm? bolts) check torque, if loose retorque, put intake back on (new gasket), if not and no sign of corrosion etc in pushrod galleries continue on with changing out head gaskets. If you do this it should take, 2-3 hrs versus 4-8 hr for a head gasket change depending on your experience.

If you are looking for a complicated explanation for this problem there is not one, that was all it is. Let us know what you find, Good luck and pm me if you

akinz · March 9, 2010

I have read a few posts about head failure and head gasket failure but haven't came across any of the same symptoms I have. I have the intake taken down and realize that there is no coolant running through the intake manifold. The leak is coming from the back passenger side of the engine. I can notice the trail of coolant coming down between the tranny and the back of the engine. I can't pinpoint exactly where the leak is.

There is no sign of coolant in the oil, or oil changes either.

Any help or points in any direction would be greatly appreciated.

Thanks

This may give you a place to look before you tear down further

Last year my 1999 gmc 4.8l 250,000 km had all the issues with the valve noisy lifters, loss of coolant with no visible sign of leaks on outside of engine.

I checked to see if i had the castec heads and did not.

Another thing I found in regards determining if you have antifreeze in you oil is your oil will not always be ' milky' on the oil dipstick to confirm that antifreeze has mixed with the oil, antifreeze does not like to mix with oil. You have to drop your oil and if it comes out kind of chunky or blobs, you have antifreeze in the oil, it will end up on the bottom of your drain pan.

I found the problem when I pulled the intake manifold off, THE TOP ROW OF BOLTS ABOVE PUSHROD GALLERIES, (11mm, not the main head bolts) ON THE LEFT HEAD HAD LOST TORQUE and subseqently antifreeze was able enter the oil pan via the valve pushrod galleries, there was evidence of corrosion, etc on the pushrods, aft lifter area.

At this point I was 90% sure I found the leak but decided to change the head gaskets, when they were pulled I found no evidence of leakage around the head gaskets gaskets.

So what I suggest, pull your intake manifold off, (only way to get at the smaller 11mm? bolts) check torque, if loose retorque, put intake back on (new gasket), if not and no sign of corrosion etc in pushrod galleries continue on with changing out head gaskets. If you do this it should take, 2-3 hrs versus 4-8 hr for a head gasket change depending on your experience.

If you are looking for a complicated explanation for this problem there is not one, that was all it is. Let us know what you find, Good luck and pm me if you

Thanks for the reply. I know I have an external leak. I change the oil every 5000kms with syntec (probably don't need to) and have never noticed any milkyness or swirls in the oil. Under the oil cap there is no sludge. It has an orange colour but that's it. It's nothing that you can wipe off with your finger. All in the top of the head and on the under cover of the valve cover looks good as well. Can't see any pool of coolant anywhere, but I suspect my leak is at the back passenger side of the head where the cooling journal is. I was tempted to take the valley off that reveal the pushrods just to see if there was any inside of there.

I'll have to take pictures tonight. Pictures are easier for people to see and nicer to look at then a bunch of words.

I don't believe I have bad castings, not ruling it out. They are 862 castings, and from what I have read, are not affected.

Keep the posts comin! Thanks again.

akinz · March 12, 2010

So I'm pretty sure I've found the leak but won't be 100% until I put everything back together and clean it. You can see where I was getting the coolant leaking down between the block and the transmission.

I'm sure the cause was the gasket on the vapour vent tube. I didn't realize that coolant flowed through this tube. (Should be called a coolant passage tube) or something like that. Anyways I'm just waiting on the gaskets to get here and in the meantime I'll be busy enough cleaning everything before I put it all back together.

I'm not going to bother with the heads since I don't want to disturb them if that's not my problem. It isn't a big deal to me to remove the intake manifold, just all those stupid injector clips that slowed me down.

mechwarrior1977 · May 1, 2010

I HAVE A 98 GMC WITH 5.7 VORTEC,I HAD SAME PROBLEM,WAS INTAKE MANIFOLD GASKET,COOLANT LEAKING EXTERNALLY,THAT WAS IN 2004.THEN IN 2008,HAD IT LEAKING INTERNALLY.SAME THING,INTAKE MANIFOLD GASKET.FEL-PRO HAS A FIX ALL GASKET KIT WHERE THE GASKET HAS A METAL FRAME.IT WAS $60 VS THE REGULAR GASKET KIT OF $20. SO FAR SO GOOD.

gmtech4 · May 2, 2010

I HAVE A 98 GMC WITH 5.7 VORTEC,I HAD SAME PROBLEM,WAS INTAKE MANIFOLD GASKET,COOLANT LEAKING EXTERNALLY,THAT WAS IN 2004.THEN IN 2008,HAD IT LEAKING INTERNALLY.SAME THING,INTAKE MANIFOLD GASKET.FEL-PRO HAS A FIX ALL GASKET KIT WHERE THE GASKET HAS A METAL FRAME.IT WAS $60 VS THE REGULAR GASKET KIT OF $20. SO FAR SO GOOD.

Aaron,the guy has a completly different engine than you

akinz · September 14, 2010

So what I thought was the problem, wasn't. I thought the coolant transfer tubes that lay on top of the pushrod valley plate and channel coolant to the heads ( 2 on each head, front and back). I'm back to thinking that it may be the head gasket. An external leak on a head gasket, I've never heard of. After I put everything back together last time, I had everything a lot cleaner then when I took it apart.

This enables me to be able to see things a little better. With a mechanics mirror and the engine running, looks like its wet, and continues to be wet between the block and the head.

I've read some other posts about the freeze plugs but I can't see anything, and don't really know where to look on the block.

I'll put some pics up when I get er torn down again.

akinz · September 18, 2010

GOTTER FIXED FELLAS!!!! I had this exact same problem with the last 2000 sierra I had. It had the 5.3, but the coolant trail was identical. Trouble was the head gasket. It was leaking externally. All the internals were perfectly fine, head was still nice and straight, popped the new head gasket on and bolted everything back up and no more leak.

I will post pictures once I get them loaded to the computer.

Hopefully this helps other people out, because I have never read about the same coolant leak anywhere on the net.

If anybody needs any help or advice let me know.

I also did find the block drain plugs as I needed to drain the block of the coolant

The drivers side will either be where your block heater is screwed in, which is easy to find, just trace the cord

The passenger side, you will need to remove the starter and will be able to see the plug. It's brass bolt with an allen head, size 10 I believe.

Later!

cottoncheeze · July 31, 2014

GOTTER FIXED FELLAS!!!! I had this exact same problem with the last 2000 sierra I had. It had the 5.3, but the coolant trail was identical. Trouble was the head gasket. It was leaking externally. All the internals were perfectly fine, head was still nice and straight, popped the new head gasket on and bolted everything back up and no more leak.

I will post pictures once I get them loaded to the computer.

Hopefully this helps other people out, because I have never read about the same coolant leak anywhere on the net.

If anybody needs any help or advice let me know.

I also did find the block drain plugs as I needed to drain the block of the coolant

The drivers side will either be where your block heater is screwed in, which is easy to find, just trace the cord

The passenger side, you will need to remove the starter and will be able to see the plug. It's brass bolt with an allen head, size 10 I believe.

Later!

I've got the same problem and will be trying my hand on that project at some point. Do you have any pics of the project when you did it? I'll need all the help I can get I'm no expert, thanks!