Finding coolant leak

I've got a coolant leak on my 98 GMC Sub. Oddly enough, a CEL code made me check the water level, and that led me to find the problem. (My wife and son normally drive this, so I don't keep too close an eye on it.)

The leak is coming down below the block, so my first thought was water pump. But the shaft doesn't wobble, there's only a little discoloration around the weep hole (and I didn't see anything come out), and there's just a little water near the end of one of the splines. I just discovered this forum (which may be the silver lining in this cloud), and shortly after discovered the intake manifold problem. I have a sinking feeling that's it...

I think I can borrow a coolant pressure tester from Autozone. If not, I'll probably buy one. If it is the intake manifold, where should I be looking? Near the bottom of the valley, either front or back? I peered around pretty well last night, and couldn't see anything, but I didn't know about the manifold problem so I may not have been looking in the right place. I certainly wasn't looking towards the rear, but the leak is coming down towards the front.

Any helpful advice on how to pinpoint this?

And does anyone know a good "Let It Be the Water Pump Not the Manifold Gasket" dance???

Doing a pressure test is the easiest way to pinpoint if it's the intake gaskets or water pump. My son and I did the intake gaskets about 4 yrs. ago on my 97 GMC Suburban 5.7L that had 115K showing on the odometer. I had been watching it for a couple months and just keep it full. Mine was leaking at the back of the manifold and running down the back of the block on the right side. It's looks hard, but if you take your time it's not that bad. We used replacement gaskets from Fel-Pro that we got at O'Reilley's and it was still dry when I sold the vehicle last fall. I changed the pink Dexi-Cool and went back to the green anti-freeze upon reading all of the horror stories on the web about it. There is an excellent thread on this site that the man documented everything as he did his and has some terrific photos. Do a search and hopefully it's still on here. Good luck...Dave

My 1995 Suburban leaked from the back of the manifold as well. My mechanic friend said it's a common problem with the 5.7L engines.

I've got a coolant leak on my 98 GMC Sub. Oddly enough, a CEL code made me check the water level, and that led me to find the problem. (My wife and son normally drive this, so I don't keep too close an eye on it.)

The leak is coming down below the block, so my first thought was water pump. But the shaft doesn't wobble, there's only a little discoloration around the weep hole (and I didn't see anything come out), and there's just a little water near the end of one of the splines. I just discovered this forum (which may be the silver lining in this cloud), and shortly after discovered the intake manifold problem. I have a sinking feeling that's it...

I think I can borrow a coolant pressure tester from Autozone. If not, I'll probably buy one. If it is the intake manifold, where should I be looking? Near the bottom of the valley, either front or back? I peered around pretty well last night, and couldn't see anything, but I didn't know about the manifold problem so I may not have been looking in the right place. I certainly wasn't looking towards the rear, but the leak is coming down towards the front.

Any helpful advice on how to pinpoint this?

And does anyone know a good "Let It Be the Water Pump Not the Manifold Gasket" dance???


check for leaks after the vehicle sits overnight....use of an adjustible mirror works great....with a powerful light ...

your problem could be a gasket, and it could also be corroded metal...If the gasket is replaced make sure you repair any corroded metal before installing the gasket ...

use of non dexcool coolant with dirty drinking water will cause these problems as well as insuffecient ratio of coolant /water mix...

drain the coolant system completely 4.5 gal....then use distilled water with the coolant...

Yeah, I saw the write-up on this site, which really looked excellent. I did the same job years ago on an old Jeep Cherokee, and it's a real time sink. (Taking off the hood made it a little less of a PITA.) There's a local shop here, well recommended, who quoted me "about $500" to do it. If it is the manifold, I just might break down and pay him, even though it goes against my religion...

I gather this is a real problem for the 5.7. But wow--distilled water. That's fairly extreme. On the other hand, if it means not replacing the gasket again, I guess it would be worth it. For the record, I don't think I've ever put coolant in this. (I had a gallon of Dexcool, unopened, so I was aware of the need.) We bought this from my parents a while back, and my dad would have used the right stuff if he added any. But it's only got about 65K on it.

J Cat, where would the corrosion be? The edge of the manifold? Wouldn't that mean a new manifold as well as the gasket?

J Cat, where would the corrosion be? The edge of the manifold? Wouldn't that mean a new manifold as well as the gasket?[/quote]

the corrosion can be in the gasket engine mating surface...your coolant must be non conductive and have suffecient coolant additives to reduce this....water with metals in it iron ,mang, nitrates...this all causes the coolant to start eating at the metal as the PH gets acidic...

normally this problem is greatest in warm climates where owners don't install the correct amounts of coolant...

it is very important to carefully inspect the metal mating surfaces and if pitted repaired with an epoxy metal filler and sanded ....this will stop repeated gasket failures...with the correct coolant and distilled water....

I used distilled water in an engine on my 83 chevy and no gaskets ever needed replacing....this engine was known to have intake leaks but 380,ooomi and it never leaked...never overheated and the radiator was with no tube build up as many have suffered ....

I did this as a result of my employment as I had to maintain laser equiptment that used a non corrosive coolant system. the water had to be pure, or the laser would get damaged...

Just a follow up. Turns out it was the water pump after all. I replaced it Sunday, and haven't seen any leaking since. I'm VERY pleased it wasn't the manifold gasket. But I've got my fingers crossed for the future...

Thanks to all who responded.

were was the leak on the pump ?back left or at the water jacketts?

Just a follow up. Turns out it was the water pump after all. I replaced it Sunday, and haven't seen any leaking since.


I replaced my 94 Sub water pump last year, the day before a trip out of state, saw a small amount of leakage under the center of the (original) water pump while underneath and looking up at it, got a lifetime warranty replacement one at Carquest. So mine was leaking at the center, didn't even know I had a leak at the time, was small, was checking power steering line tightness and noticed it, but these things don't heal themselves.