Chevy Vortec Mystery Coolant Leak

January 4, 2009 by  

If you own a Chevrolet or GMC Truck with a Vortec Engine, you will eventually encounter the "Mystery Coolant Leak".

At first, it's just an occasional low coolant light coming on. The coolant level is low, but there aren't any leaks visible on the ground. Where is the coolant going?

Eventually, months maybe, there are telltale drops of coolant on the drive way after the truck sits overnight. On the frame underneath may be a drop of coolant about to drop right in the center of the truck. It's starting to look like it needs a water pump maybe, but when we climb underneath the pump itself is dry. What's going on.

This is probably one of the most recurrent problems I see with Vortec engines, no matter the size. Careful inspect on the top front corners of the engine will show moisture where the intake manifold meets the cylinder heads. The area is usually hidden by the air conditioner compressor and alternator and is difficult to see. As the leak gets worse it will become very evident. Be assured, until it is repaired in will get worse over time.

Leaky Vortect Gasket

Leaky Vortec Lower Intake Manifold Gasket

The problem here is GM's use of plastic intake manifold gaskets. There were Tech Bulletins circulating in the mid 90's about more info

the bolt torque settings being way too tight from the factory, resulting in the plastic cracking prematurely. The torque has been reduced, but it has only delayed the failure until the vehicle is out of warranty.

Early on in the failure, the coolant just seeps out. Eventually it runs out rapidly; sometimes even squirting over the grill. On rare occasions it leaks internally into the engine oil pan.

The fix is to remove the intake manifold and install a new gasket set. It is not a hard job, but the Vortec is a maze of plastic parts and connections. Some are fairly fragile and need to be handled with care. Take careful evaluation of your abilities before jumping in.

Here's one tip, if you do decide to tackle it. On most Vortec Engines the upper and lower halves of the manifold do not need to be separated for the lower gasket replacement. However, if the engine has high mileage, say above 120,000, it is smart to replace both the upper and lower gaskets.

Fel Pro makes a problem solver gasket that has a steel base instead of the OE plastic gaskets. They are a bit pricey at around $90.00 but they will never leak again if installed properly.

The Vortec is a great engine, but it does have some pattern failures that seem pretty common to them all.

Good luck and happy wrenching.



28 Responses to “Chevy Vortec Mystery Coolant Leak”

  1. Geoff on January 4th, 2009 5:24 pm

    I’m beginning to see a lot of my friends with GM trucks with Vortec engines having to have the intake gaskets replaced. You would think GM would have redesigned those things by now for more dependability.

    Good read. Thanks.


  2. Chevy Truck Bill on February 6th, 2009 9:28 pm

    I’ve driven Chevy’s all of my life and am surprised at all t he plastic stuff showing up on the engine. Things I never thought would be made out of plastic. I still think they make a great product. I hope they get all their troubles ironed out. I’d hate to see them go under.


  3. Jason Mertens on February 7th, 2009 12:32 am

    I own a 2002 Denali with the 6.0 Vortec. I am starting to get a small leak under the car. Doesn’t look like the water pump so could it be the gaskets on the intake manifold? The rig only has 64000 miles on it. I knew I should have bought a Ford. This is the worst $50000 I have ever spent.

  4. Intake Manifold Leaks | The Frugal Car Owner on March 13th, 2009 1:46 pm

    […] recently posted of a Vortec Engine intake mainfold water leak.  This repair is very typical of all the GMs with plastic gaskets.  The plastic cracks around the […]

  5. Chad Spriggs on August 14th, 2009 3:25 pm

    I have a 2005 GMC 2500HD with the 6.0L engine. I have recently noticed a very small puddle of coolant under the truck . Thought it was the water pump had went bad . But after close inspection the water pump isnt bad but it looks as if the water pump gaskets where the pump meets the engine block are leaking. Other than that it is an excelent truck ! But I guess that is just somethin to look for .

  6. Chevy 5.3 v8 issue on March 7th, 2011 4:03 pm

    […] Silverado and it needs fluid added a lot less often. The link is to just an article about this. Chevy Vortec Mystery Coolant Leak | The Frugal Car Owner The article below is of a service bulletin that might be of interest as well. Engine – Coolant […]

  7. Norm on March 7th, 2012 7:10 pm

    this looks like the same problem I think I have. It’s doing the same thing and in the same location, behind the AC compressor. I have a 98 Chev Cheyenne with a 305 cu in (5.0 Liter) V-8 Vortec, with 150,000 miles. For the last year, it would be low on coolant by a quart or so. Filling it at night and finding out it was low the next morning told me it wasn’t from overheating, but rather a leak. I couldn’t find out where, but now that it is streaming out in the location describe, I think I now know what it is, and hopefully that’s all it is (& not a head gasket!). I am scheduling up the repair. Thanks for the tip on this vortec problem.

  8. allan on November 25th, 2012 11:19 pm

    I have a 2500 with a 6.0 I have been loosing coolant somewhere for quite a while and it is getting worse. Would this leak also cause a reduced engine power code ? I have read elsewhere that it is sometimes caused by TPS and or throttle body wiring.

  9. Craig on April 3rd, 2013 7:48 pm

    I have a 98 Chevy C1500 with 224000 miles . Water was miss from time to time . One day water in the oil . I pulled it all out had a shop redo another motor [5.7] vortec .// New every thing even the spider injector [ up dated ones ] hope to have it running this week end . I have been looking at a lot of info on different fourms . I thinks most of it is good info .

    good luck …

  10. Mike ellis on April 9th, 2013 4:15 pm

    The same thing happen to me on the way to my dentist in haltom city texas.

  11. Jim Denis on September 24th, 2013 8:53 pm

    Just had a new engine installed in my Chevy 2000 1/2 ton. Last year I put $8300 in it replacing what seemed like everything that could go wrong and then low & behold the coolant began to disappear with no tell tail signs of a leak. After adding coolant for several months I discovered what seemed like a “clay like gunk” in the oil pan only to discover that the coolant was leaking into the oil thru the head or intake gasket I was told which was going to cost about $1400 to fix. Nothing last forever. Hopefully the new engine will do better, no plastic gaskets on this, I learn from my mistakes. Praise the Lord!!!

  12. Francis Parker on October 11th, 2013 10:15 am

    I have an 06 silver ado with a 5.3 liter engine that continues to overheat at various times without any obvious leaks. The truck will not run hot for months then all of a sudden the needle shoots up to hot hot! It boils and shoots out of the overflow. All coolant lost.

    Had the radiator cap replaced and one of the heater hoses. Has a new water pump 1 year old. Had a new engine installed before this happened. Had radiator flushed twice and now a new thermostat. Shops were putting the green antifreeze in and the last person who looked at it put dex cool in. Any ideas on whether that will make a difference????

  13. Jim on October 23rd, 2013 7:34 pm

    you could of bought the Ford and then have the spark plug pop out 98-03 and strip out the threads ..or the 2004 and have the spark plug break off in the head …PS I can fix the Ford plug hole and I charge 300 per hole …permanent fix…Ford should of done the STEEL inserts in the first place …so to each his own …they are all built like crap anymore honestly ….
    Thanks Jim
    2000 K2500 4×4 ( replaced gaskets myself after Autotire did em 2 yrs earlier)
    1988 s-10 383 350th
    1981 ElCamino ( ratt rod work ride LOL )

  14. Robert Nobel on December 26th, 2013 7:49 pm

    97 chevy 1500 pickup.coolant dumping down left side of block. towerd back of eng.on to oil filter.poss. intake gasket.??

  15. Eric on January 9th, 2014 11:09 pm

    Yes, most likely is the intake gasket. These things are really a poor design.

  16. Larry on February 3rd, 2014 5:19 pm

    I just pick up a 2001 Chevrolet pick up truck with the 4.3 v6 did a tune up on the truck it ran ok for about 3 days and now I see coolant dripping on the ground now its going to cost me 1,500 to replace the intake gasket damn gm junk iam going back to dodge a far better truck

  17. Eric on February 4th, 2014 10:30 pm

    Larry, sorry to hear your bum luck. It’s a pattern failure. In other words they are all just about doomed to have it happen. I would think $1500 is a bit steep for a gasket repair. I looked the flat rate up on, which is mitchell-on-demand’s new site.

    The manifold should bill 4.9 hours with AC. Around here that’s about $350.

    The gasket set retails at NAPA for $67.00. Then a gallon of coolant, maybe.

    At the worst dealership around I would expect it to be less than $500. Your shop may be quoting the entire replacement manifold, which is not usually needed, unless it has cracked from overheating.

    Good Luck with it, whatever you decide to do.

  18. Tim on April 10th, 2014 11:39 am

    Anyone with a GM composite intake (Buick, Chevy…) seeing this disappearing coolant symptom: get it checked NOW! Use the best Fel-Pro replacement gasket.(5.7= FP MS98000T). If not, you’re probably driving around with coolant in your oil, which can end up costing a lot more than the repair you’re delaying paying for. I used the GM gasket 90,000 miles ago, gotta do it again. The 40 bucks saved not buying the Fel-Pro sure doesn’t look worth it now!

  19. Eric on April 10th, 2014 11:08 pm

    This is absolutely excellent advise. Not every manifold gasket leak will leak internally as well, but the chance is still significant that it will and the financial damage is very significant. (to your pocket). Thanks for sharing.

  20. kevin on December 18th, 2014 4:11 pm

    I have a 98 chevy c1500 has the 305 I just bought it a couple weeks ago and off and on I can smell a coolant leak off and on I only have to but a small amount of water in once a week but iv looked everywhere and do not see any leaks at all

  21. Brent Croom on January 1st, 2015 1:31 pm

    I have a 1996 GMC Z-71 with a 5.7 vortec. Have noticed my coolant was disappearing a little here and there over the last few years. I know very little about this stuff!!! Can anyone tell me if my engine has that GM composite intake. Over the past week or so I saw a small puddle of what I think was coolant under the truck. Took it to the shop and my mechanic said after a pressure test that is was my intake leaking coolant!! I am supposed to get it fixed next week. I like my old truck but seems over the past few years it is costing about 1500 a year to keep it going!!!

  22. Eric on January 1st, 2015 6:31 pm

    Hi, Kevin, I’m sorry it has taken a while for me to see this. It got hung up in the spam filter for some reason. The Vortec leaks can be tough to locate. With all the plastic intakes the leaks may only be there when the truck is going down the road and fully warmed up. The wind uder the hood blows it all away before it can drip on the ground.

    Look really good around the areas where the lower intake manifold meets the cylinder heads. Small leaks will cause some buildup of minerals and chemicals in the coolant that stick around after the water evaporates. If it is coming from the weep hole on the water pump you may only get the mineral buildup initially as well. A small hand coolant pressure tester is usually needed for the little leaks. It will allow you to put about 15 psi of pressure on the whole cooling system and force the coolant to leak while you are looking at it.

    Good Luck.

  23. Eric on January 1st, 2015 6:38 pm

    Hi Brent, thanks for stopping by here. The Chevies in that vintage are nice trucks. When we keep them up they seem to last forever. The trucks have some design problems, though. The plastic intake manifolds and gaskets are a big one. The pretty much will all leak and needs some attention eventually.

    The fuel injection system inside the intake manifold is also problem-prone and expensive. At least the fuel pumps in that era were relatively cheap, compared to the units starting in around 99-2000.

    As to your question, you should have the engine with the plastic top end. Just pop the hood. It should be obvious that the upper part of the engine is black plastic. Have your mechanic install the better “Problem Fixer” gaskets. They are metal core gaskets instead of all plastic. The should last a lifetime. They run about $80 instead of $20, though.

    Good Luck, Eric

  24. Cameron on January 8th, 2015 8:38 pm

    I clearly have an intake leak on my 98 5.0L vortec. Do I have a head/head gasket problem? I’m fouling plugs very rapidly. Should I just pull the heads to be safe if I’m going to do intake gaskets?

  25. RICHARD HARRISON on January 14th, 2015 11:19 am

    I have a 2007 Silverado Classic 2500 Ext.Cab 8.1 L. It has 8400 miles, on 12/26 engine stopped, had it hauled to Chevy dealership. They said it dropped #6,said blew the top off.I have talked to 5 chevy mechanics all say it should not have done that with 84K.3 said it had to be a flaw in cylinder.Have you heard of this problem? Or have idea of what could have caused this?

  26. Alan on January 28th, 2015 9:53 pm

    My Dad called me to help him with a coolant leak he could not find. When I poured the coolant into the radiator, I seen the coolant pouring out of what appears to be a weep hole in the intake manifold under the upper radiator hose. He has a 1997 Chevy K2500. I’m certain the intake manifold gasket is leaking. The engine is a 4 year old crate motor with about 30,000 on it.

  27. Ray on February 6th, 2015 9:54 pm

    I have a 2000 GMC with 268000 miles on it. Bought it with 240000 on it. When I bought it, it was needing some attention. It is the Z71 4X4 with the 5.3 these engines are famous for piston slap in the early models. When I start this truck every morning it sounds like it is tapping loudly. I let this motor warm-up before I rev this motor and it still seems to do me fine. It still has plenty of power for my pulling I do. I pull a older 5th wheel that’s a 25ft with no problem. My fuel mileage drops from 17 to 11 miles per gallon though. I love this truck because I have no remorse over using it. I don’t get stupid and punish it in the mud, but I’m sure not afraid to bushwack it a little, or put the pedal to the rug to get something done. This summer I usually do a weekly visual inspection, and fluid check. A small two inch puddle of antifreeze lie directly under the crank pulley. So I got out my little spot light and cralled under the truck to see what I thought was a water pump seap hole leak, got the pump off to find out it was the gasket between the pump and the engine block. Even though the pump didn’t appear to be a problem I put a brand new one on it. At this point i also put a new thermostat ,fan clutch , belt, upper,and lower hoses,and antifreeze. That was the best $500 I spent on the truck since I bought it. I really believe this truck will see 300000 miles before I have to put her to rest. I haven’t noticed the intake leak problem yet, but I’m sure to use the tips you have given me on the locations for discrete leaking locations. I’m sure that I will get the pleasure of doing this repair before I retire this truck. My wife will be getting a new car before I get a new truck LOL.

  28. Tim on February 21st, 2015 6:04 pm

    I have a 2000 Chevy Silverado and I have a leak on the bottom it’s coolent but the gaskets are all good would this be a freeze plug and how hard to replace its on passenger side by the starter

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