Plastic Engine Parts


The Mystery of Neil’s Truck


The image to the left is the under-hood of a Chevy pick-up.  The customer’s concern was for a slow loss of coolant and this coolant loss was a bit of a mystery.  Neil, the owner of the truck, reported that he would have to add a couple quarts of coolant every two or three weeks. His truck was always parked inside a garage and there was never any evidence of a coolant leak.

This problem is seen primarily on GM’s cars and light trucks.  Here’s how it starts.  The vehicle owner will notice that the coolant level slowly starts to drop.  Usually there will be no sign of coolant on the ground.    A pressure test of the cooling system could be inconclusive.  You may get a brief smell or there may be no smell.  The  “no smell”  can be the dangerously expensive one.  Diagnosis of this mystery coolant leak requires a couple of inspections.  The first inspection is of the engine oil level, dipstick and oil filler cap.

What are we looking for?

An overfull reading on the oil dipstick can indicate 2 possibilities;  The engine oil is just overfull or there is coolant in the engine’s crankcase.

Why would oil in the crankcase result in an overfull condition?   Coolant/water is heavier than oil.  The coolant will settle to the bottom of the oil pan causing the oil level to rise in the engine.   If this condition is found, another clue should be present.  The oil filler cap and possibly the oil dip stick will have foamy build-up that is best described as a milk shake looking goo.  This goo is the result of engine heat causing the coolant/water to evaporate and rise like steam escaping from a boiling pot of water.  The Moisture condenses and collects in the high points of the engine.

The Danger

In the event the engine’s oil pump should pick-up coolant, it will feed the coolant to the engine’s connecting rods and main bearings…, bang goes the engine!


The Good News, the Leak is External

The external leaks can be elusive.  We first look for signs of coolant or stains on the engine block.  Here’s what’s neat about this problem.  In the early stages of this type of failure, coolant will only leak while the engine is heating up.  Once up to operating temperature the the leak stops.  This also means the heat of the engine will evaporate the small amount of coolant before any signs are seen under the vehicle or on the ground.

This condition can often be caught by pressurizing the cooling system when the engine is cold.  Start the engine and as it warms up and watch for leaks.  At just the right temperature the leak will present itself with the additional pressure on the cooling system from the pressure tester.

Pressure testing on Neil’s cooling system found the cause for the mystery.  A failed intake manifold gasket was allowing coolant to slowly leak out of the engine.  If Neil had ignored this problem he could have been buying an engine. Even though the repairs are still going to cost money, it is good news.


Now the Fix

Replacement of the intake manifold gaskets requires the removal of the intake manifold. This is easily said but as you look at the picture to the left you can see that there is a good amount that has to be removed. Clearly, this is no small adventure.

The cause for this intake manifold gasket failure? Plastic! That’s right.. plastic, the intake manifold gasket from GM is/was made of plastic.  The intake manifold is not just about getting air into the engine. It also has coolant passages from the cylinder heads and the thermostat is located in the intake manifold.   With age and exposure to coolant, the plastic becomes brittle and cracks. This results in failure of the sealing surface.

So why would the intake manifold gasket only leak at certain engine temperatures in the beginning? You have to realize, that the engine is made up of dissimilar metals. You’ll have the iron of the engine block, aluminum intake manifold and cylinder heads that can come either way, aluminum or iron. We know that metal expands as it heats up. The problem  with dissimilar metals is they expand at different rates, in different amounts. Now throw a piece of plastic in between and you have a recipe for pending doom.

 Poor Quality Original Equipment


The aftermarket was quick with the fix, they came up with a replacement intake manifold gasket that was far superior to the plastic ones provided by GM. To the left is an image of the failed intake manifold gasket. Click on the image for a better view.. That squiggly kind of light blue looking ring is the seal that is suppose to keep the coolant inside the engine, not outside. The distorted areas are where the coolant was leaking. If you look at the bottom of the opening you can see that the ceiling surface is starting to fail. If this section had failed completely, coolant would’ve entered the crankcase of the engine. Coolant in the engine oil could have resulted in a catastrophic failure of the motor.


 Aftermarket to the Rescue

Here is a close up of the replacement gasket.  Click on the image for a better view..When we perform this service to our customer’s vehicle they will only receive the new and improved gaskets.  Not too long ago GM smartened up and changed their gasket design as well, guess what it looks like? If you guessed pretty much like the replacement aftermarket gaskets, you’re right.

When it was all said and done Neil’s truck was sealed up as tight as a drum… no more coolant leaks.

Today’s automotive world is changing at a blinding speed. It is not uncommon for manufacturers to change the design part way through the year. With so many changes there will be problems. One thing we’ve learned is that the aftermarket is quick to respond with fixes for design problems in today’s vehicles.



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At the Northwood Garage we proudly provide expert auto repair and tire service to Northwood, Strafford, Nottingham, Epsom, Barrington and Deerfield.

Northwood Garage… Keeping your Car Good to Go! Since 1955



  1. Hey Jim, did you notice this problem was with dexcool only? (pink stuff) I’m a retired GM mechanic and have only noticed this problem with 96 and newer engines. I never heard of a problem with 95 and older (green anti freeze).

  2. if you get your intake gasket fixed and there is no sign of head gasket failure do your have to get your head gasket
    fixed also. 2003 grand prix

  3. Jim, Can you tell me when (what year) GM finally addressed the plastic gasket issue? Thinking of purchasing a used 2003-2005 Buick Lasabre and wondering if the issue was addressed prior to this time. Also, I have been told the red coolant was part of the problem, so I have been using the green in my 1996 Park Ave. for the last 7 years and 100k miles after having my gaskets replaced in 2006. No problems since 2006 with the mileage now at 211K.


  4. David Signorelli says:

    Any idea what the average cost of intake gasket replacement for a 2002 Chevy S10 4.3 6cyl would be?

  5. Hey Jim,
    Just stumbled across the site after searching for reasons “why my truck keep blowing gaskets”. Currently my ’05 GMC sierra is in the shop for the third time in 2 yrs to have the intake gaskets replaced. Not a single mechanic at the dealership had an answer for me as to why I have to have this done again. Thanks to your site and the May 2012 article about Neil’s truck, I have my answer, cheap GM plastic. Hopefully, the new and improved GM gasket is being installed in my truck this go around and not another piece of plastic.

  6. Gloria Clements says:

    I’ve had the intake manifold need to be replaced twice and was wondering if gm had any recall issues . I own a Chevy Monte Carlo 3.8 engine

  7. Tim Farmer says:

    I have a 2008 chevy 1500 silverado, it has a 5.3L with AFM (what a pos). Well recently I’ve noticed as I’m driving the engine will increase and decrease rpms 2-300 rpms. I’ve changed the tps but to not avail, I have cleaned the throttle body with mass air cleaner carefully wiping out around the throttle vane and yes it was dirty but this didn’t help either. No loss in radiator fliud but I’m suspecting the intake gasket may have a vacuum leak. A penny for ur thoughts? Thanks

  8. Wayne (Race) Cartwright says:


    I can’t recall when I’ve seen a better written or more useful page. Thank you so much for sharing your knowledge with the rest of us gear heads.


  9. Richard Williams says:


    I have a 91 Camaro R/S 305 engine which I let sit for four months without driving and decided to drive it into the city. On the way I notice the engine get weak and pick up speed again, upon getting to a gas pump to fuel up, I notices steam coming from under the hood, I rasied the hood to find the steam coming from the throttle body. I tried cranking it but had to let it sit for about 20 min. and it started back up. Long story short I’m thinking the intake gasket is gone, the engine still has power, but the oil dip stick is showing the sign of being overfilled. There is no steam coming from the tail pipes.

    My question is in replacing the intake gasket would I need to replace the oil pump, throttle body or anything else. I haven’t drove the car for a year or more and it still starts. I had been debating on replacing the engine untill just the otherday it came to me that it could just be the intake gasket due to me noticing coolant under it on the front of the engine sometime ago.

    What you suggest???

  10. Remarkable! Its truly remarkable article, I have got
    much clear idea about from this paragraph.

  11. I have a 97 Chevy Blazer V6 4.3 L. I need my intake manifold gaskets changed,, I was wondering how much it might cost for parts & labor ?

  12. Our 2006 Toyota Carolla has had the engine check light come on twice now with a PO 171 code.
    Both time it was when the weather was at freezing or below.
    Both times I cleaned the MAS with the correct cleaner and cleared the codes and the light did not come back on again because the weather got warmer.

    I went to the Toyota dealership and asked about the intake manifold gasket , the service manager who had worked there many years said they had never replaced the intake manifold gasket on the PLASTIC intake manifold.

    Also no parts houses or dealers had the gasket in stock.

    Makes me wonder where the air leak is and if the cold weather caused the plastic parts to shrink enough
    to cause an air leak. I was tempted to put some sealant around the O ring where the MAS fits into. But I did not because I know those sensors can be ruined with some chemicals.

  13. Our 2006 Toyota Carolla has had the engine check light come on twice now with a PO 171 code.
    Both time it was when the weather was at freezing or below.
    Both times I cleaned the MAS with the correct cleaner and cleared the codes and the light did not come back on again because the weather got warmer.

    I went to the Toyota dealership and asked about the intake manifold gasket , the service manager who had worked there many years said they had never replaced the intake manifold gasket on the PLASTIC intake manifold.

    Also no parts houses or dealers had the gasket in stock.

    Makes me wonder where the air leak is and if the cold weather caused the plastic parts to shrink enough
    to cause an air leak. I was tempted to put some sealant around the O ring where the MAS fits into. But I did not because I know those sensors can be ruined with some chemicals.

  14. This water coolant leak problem is just what I’m experiencing. Thanks for the explanation. I haven’t fixed it yet, but feel better about tearing it down thinking this is my problem. Thanks For The Advise.

  15. chriscloud says:


    if my intake gaskets failed internally what would be the best way to flush out my engine it pulled up a engine missfire on a trouble code and i narrowed it down to the intake

  16. Can someone please tell me what fair price for this repair would be . I have a 2004 Chevy impala

    I would suggest checking with


  17. I would suggest checking with


  18. My 99 S 10 4.3 started leaking coolant badly right behind the air cond. compressor where the intake manifold bolts onto the head hope it’s just the gaskets and not a blown head gasket .

  19. Miranda says:

    Hi, I have a 2003 Grand Am GT. It’s my first car and she has no power. :( I’ve done plugs, wires, air filter, coil pack checks, O2 sensor, fuel filter and a vacuum gauge test. It’s 17 in-Hg at idol but fluctuates about .5. This is what I’m thinking in order.. Fuel pressure test, Injectors, Intake leak, cam shaft, bad transmission. What do you think?

  20. Chelsea says:

    I have a 98′ Chevy Silverado and I had it looked at recently and they told me that it was my vacuum leak at intake manifold causing a squeaky noise, what part should I be looking for to replace it and how easy or how hard its it to do it?

  21. I have a 1997 mazda 626lx and I have recently come to some troubles I have no power cannot go over 45 mph I can’t rev over 3500rpms and when I get close to it it sputters and shakes and won’t go no more I have changed plugs wires air filter maf sensor and the valve cover gasket I changed the valve cover gasket because I had what I think was oil in cylinders 1,4. I replaced that a couple days ago and I got all of it out and I pulled my spark plug for cylinder one and it had stuff in it again would this be caused by a head gasket or intake manifold gasket I also looked into having a clogged cat because it had some symptoms like it I looked more into it after I had changed the valve cover gasket thinking it was clogged from that but I’m not sure can you please help me?

  22. devin k says:

    i have a 350 chevy in my k10 and i have a bad miss at all rpms. i replaced everything fuel wise besides the injectors and wires to the pump. it has new intake gasket that doesnt leak. basically a whole tune up was done. any ideas? it is a tbi.

  23. Edgar ferrer says:

    I have a 01 impala and I was gone for like a year so when I get back I find that when my car was trying to be moved once started the manifold intake blew up. My question is is my engine totaled or should I just replace the manifold?

  24. Need answers: I have a 2006 Mitsubushi Montero and about two months ago the oil light came on. So I took it in and was told it was the Head gaskets. So I took it to a guy we had taken the car to before. 22 days later and $3600 dollars later we got the car back with Head gaskets replaced. Drive out of the shop and the Engine needs serviced light comes on so I call him and he said the code was for catalic converter and to just keep bringing it in so he can check the code. He thought the light would go off after some time. The car was making a horrible noise and running horribly and had absoluately no power. Light has never gone off and so we took it back and now he is telling us that it is the Manifold. Wouldn’t they have checked that before they replaced the EXPENSIVE head gaskets? So, now we are talking another couple thousand $$. Any comments and what we can tell the mechanic?

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  27. Hey Jim I have a 89 k1500 pickup and recently it started having problems firing up..I can always get it started after a go or two and have to give it gas..sometime it starts right up..temp has nothing to do with it’s not electrical and I have fuel pressure.there’s a slight oil leak on the back driver intake gasket.could that be the issue?

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  29. Marvin Von Renchler says:

    1997 Firebird. Water leaks into oil and it looks just ike you said. A milkshake sort of tan w foamy stuff. Did this problem stop by a certain year? Did GM finally get wise? This should be a class action suit

  30. I love what you guys tend to be up too. This kind of clever work and coverage!

    Keep up the awesome works guys I’ve you guys to my blogroll.

  31. I am currently having my intake gasket changed on my 2003 Chevy Blazer. I had it inspected because I was having to put antifreeze/coolant and water in it. It is at the shop now to get it fixed. When I was getting in to start it up to take it to the shop I noticed that it started dragging when tiring to start it up. I has never done this before until now, it usually fires right up without a problem. Granted it has been colder these past few days and I am assuming that it could be from the cold but with the gasket leaking I am wondering if this could be a factor in it, and would replacing the gasket also solve this problem? Any comments on this would be greatly appreciated for this is my only vehicle and can’t really afford to do much with it at the moment.

  32. Tim Nelson says:

    I just had a car fire in the garage, the fire inspector said the car caused the fire. A GM Pontiac G-8, 6 cylinder 2008,
    was caused because gm didn’t put a shield over the exhaust manifold and have faulty valve covers, so when the car is turned off pressure builds up in the valve covers and drips down onto the hot exhaust and ignites the car.

    Have you heard anything about this, also Pontiac Gran Pree and Buick LaSabre ?

  33. So today I took my car in to AAMCO to get an intake leak fixed. I had no antifreeze in my car. My car was in the shop from 11-4 and paid $787 to get it repaired. When I was driving it home I notice smoke and thought maybe they spilled coolant or something. I went to work later and started to smell something funny. When I got home I look and almost all my antifreeze was gone! What are the chances it would still be leaking. And to be honest my car never ran hot, smelled funny, or smoked even without antifreeze it ran rough but now it’s even worst and is on the borderline of running hot. What should I do? I called the shop but they are closed til Monday. I am very displease with this company that supposedly fixed my car!

  34. Also I have a pontiac 2004 Grand Prix.

  35. Is it necessary to replace the lower intake as the aluminun is pitted to a depth of like 1/8 inch?

  36. Thank you for the good writeup. It actually was once a amusement account it.
    Look advanced to more delivered agreeable from
    you! By the way, how can we keep in touch?

  37. Barry johnson says:

    I have a 2000 Chevy blazer , coolant level keeps droping , have to add daily, doesn’t t probably due to continually adding coolant. Can coolant get into the oil by way of the lower intake gasket? Noticing no leaks, lost please help

  38. Jim I have a ? I have a 96 blazer lt n I had the milkshake effect with the coolant mixing with the oil so we drained it replaced head gasket ,theromastat, air filter ,oil filter n the battery n had alternator tested n it still won’t start it turns over but won’t start do u have any advice or a answer of what else it could be?

  39. I have had my water pump replaced twice recently and still smell antifreeze in the cabin of my 1997 Buick Riviera. Today my mechanic said the upper intake plenum needs replaced. This has been the best car ever for me.. bought in 2002 with 50k now has 200k ..

  40. I have a 2003 Chevy blazer , my intake manifold gasket went . Is $625 a reasonable price for repair ?

  41. It seems to be in range, are they replacing any other parts besides the intake gaskets? Thermostat, ignition parts,etc? You’ll save labor time replacing such items while replacing the intake gaskets

    To get a better idea for your area go to

  42. Depending on the area of pitting, but in most cases yes. The pits can be filled with a product like Permatex Ultra Black Gasket maker. Clean and fill and smooth to surface. Allow to cure and assemble.

  43. It’s not the Dex-Cool in and of itself. Dex-Cool may not be the greatest coolant but GM deliberately selects components with planned failure in mind.

    I work with a former GM engineer & one day I was bitching about my work van’s legacy of engine issues. While talking about this he informed me that failures like this are a CHOICE that GM management makes. He said that the design teams (including those he was on) were required to present multiple options for assembly components and that the parts management selected for inclusion on the assembly line were chosen based on their ability to meet the BARE MINIMUM REQUIRED to pass the warranty period.

    In other words: if the motor had a 70k warranty on part “X” and the three options have a predicted lifespan of 75k, 100k and 300k then the 75k part would be selected EVEN IF THERE IS NO DIFFERENCE IN COST for the better, more durable parts. The rationale given to him was that GM management wanted to ensure business/revenue in the dealership service departments.

    As a victim of this particular intake gasket issue on both my work van and my son’s GMC (which spun a bearing this week) I will — NEVER — own or buy another GM product.


    Not new. Not used. Not whatever.

    I also insist that until this van is no longer operable (it’s a service van) that any repairs will NOT use “Genuine GM Garbage Parts”. Why? My van is on engine #3 and even that one had to be rebuilt on the bottom end. All three of the engines were killed by the intake gasket issue. The original engine failed with the intake gasket & spun a bearing w/ the coolant… the 1st salvage engine had the same problem and was returned and the 2nd salvage engine ‘appeared’ ok but blew the intake gasket a few months later.

    Does anyone remember when a 5.7L (350) Chevy was a great motor? I do – but I’ll never own another one. Or any other GM piece of manure.

    Now my son’s GMC Jimmy (4.3L) has spun a bearing after we replaced a bad intake gasket approximately 6 months ago. Does GM think we’re going to rush down to a dealership to pay for a $3100 engine replacement? Hell no and my next van will be a Sprinter or Nissan – I don’t even want American now.

  44. I have a 95 LT1 z28 camaro with a lt4 intake and it has been getting g really hot. Ok now the oil is milky, can this just be the intake where it is a bigger intake than supposed to be on my car. I have light blue smoke and the radiator smells alittle of gas fumes. I have be taking it apart after work. I have the intake off. It also started leaking g oil from the front of the intake. Please say it’s just the intake. Alot of work still to go to get the heads off.

  45. My 05 grand am overheated yesterday can not go more than 7 kms without red line. Oil and water coming out of lower side of driver side engine. And my water pump made a noise when revving a little. Should I replace both or trying water pump the lim

    I’m curious

  46. Let’s tell it like it is. Car makers have always been about profit. But in the past, people still had more moral principles. So one could say that domestic cars technically were more reliable than they are today. Today, most corporate businesses have been taken over by the greediest, most rotten people. They are incompetent. And it shows in how their parts are poorly designed. Its clear to me that car makers are designing vehicles to fail.

    How many damn vehicles does a car maker have to make to get it right and keep it right? Not many. Because they are not trying to get it right. Its all a big scam to roll in the dough. With servicing and parts.

    Chevy and Ford both make poop. But Chevy is by far the worst on the planet. I give the Koreans more points than I do GM. And we all should know by now that Toyota is STILL king over domestic cars. Even with their own share of issues.

    I used to like GM. But its not GM anymore. Its the new GMO of cars.

  47. Before you just replace the water pump, have the cause/source of the water and oil leak. Knowing just what is wrong ask for an estimate to be sure the cost of repairs. The coolant/water & oil leak together are concerning. Get the whole picture before spending money…

  48. Hi, I’m having a leaking problem in my 2005 chevy silverado 2500hd, my driver side floor is constantly wet fix the sunroof, the doors rubbers and still leaking, PLEASE IM OUT TIE WITH MONEY, IF YOU NKOW ABOUT THIS ISSUE PLEASE IM BEGGING U, HELP ME, IS VERY ANNOYING. THANK YOU

  49. Has the windshield been replaced in this vehicle? We seen poor replacements start leaking months out. Usually the water will come down the a-pillar and run along the metal behind the dash. May I suggest that you remove your carpeting and shake some baby power on the floor. The water will leave a trail, which should help you track the source of the leak.

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