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Bad intake gasket?

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Old 09-22-2008, 07:17 PM   #1
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Bad intake gasket?

Today on my way to work, my truck started to smoke a lot out of the tail pipe. I let it sit all day and started it up at 3 pm. Ran fine with no smoke. When I started it at 5 pm, it smoked a lot again and quit after I started driving down the road. When I got home and pulled into the garage, I couldn't see where I was because of all the smoke that was coming out of the tail pipe. I also noticed that there was a lot of fresh oil on the floor that wasn't there when I left this morning. The motor seems to run fine as far as I can tell. The intake gasket was replaced at 100,000 and now it has 160,000 on it. Also, it won't shift into 4 hi, only 4 lo, and the heat and air don't blow out when accelerating, only when coasting. Can a bad intake gasket cause a possible vaccum leak? Any help is appreciated.
Old 09-22-2008, 07:58 PM   #2
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Re: Bad intake gasket?

well, it sounds like you have 2 different problems.... you obviously know that its vacuum leak causing your climate control problems..... the vacuum line comes from around the drivers fender, and goes to the intake manifold.... im sure there is a hole, or break in it.....
2nd, is it black smoke, blue, or white? if its black, id blame the injector assy. every time..... if its blue, it may be the intake gasket..... if its white, well....... good luck
Old 09-22-2008, 08:12 PM   #3
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Re: Bad intake gasket?

It's a bluish white color. There is a lot of oil on the ground under the back of the motor from what I can tell is the back of the intake. I also think that there is oil in the antifreeze. There is a milky substance in the overflow tank. All of my problems seemed to start at the same time. A couple of weeks ago I had a plugged cat converter and I wonder if the motor built up too much pressure and caused the intake gasket to give out.
Old 09-22-2008, 08:43 PM   #4
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Re: Bad intake gasket?

Quote: Originally Posted by ace16a
It's a bluish white color. There is a lot of oil on the ground under the back of the motor from what I can tell is the back of the intake. I also think that there is oil in the antifreeze. There is a milky substance in the overflow tank. All of my problems seemed to start at the same time. A couple of weeks ago I had a plugged cat converter and I wonder if the motor built up too much pressure and caused the intake gasket to give out.
yea, thats a decent bet..... but, if the intake gaskets are pulling in oil (enough to smoke) then an external leak isnt really a clue to anything, cuz tho they may be the same problem, they are two symptoms that dont prove anything..... like an external leak doesnt mean ur pulling in oil, and pulling in oil doesnt mean you have an external leak
Old 09-22-2008, 09:15 PM   #5
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Re: Bad intake gasket?

I guess I'm just asking if I should replace the intake gasket or pull the motor and rebuild it. I usually ride my motorcycle but with the weather starting to get colder and wetter, I don't have a lot of time to be without my truck. The other option available is to pull the 4.3 and swap in a 5.0 TPI that's in my Z28 right now. I just recently finished rebuilding a TBI 4.3 for my brothers 1989 work van that was a pain in the a$$ so I'm not looking rebuild my motor if I don't have to.
Old 09-22-2008, 09:19 PM   #6
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Re: Bad intake gasket?

Just a thought. Couldn't oil be sucked into the intake on the piston's down stroke and pushed out on the up stroke? And the same with the coolant? I've had to fill the radiator every couple of weeks of use and I always smell antifreeze.
Old 09-23-2008, 04:13 PM   #7
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Re: Bad intake gasket?

Quote: Originally Posted by ace16a
Just a thought. Couldn't oil be sucked into the intake on the piston's down stroke and pushed out on the up stroke? And the same with the coolant? I've had to fill the radiator every couple of weeks of use and I always smell antifreeze.
Not likely because you don't have any oil passages near the piston. The intake manifold is almost always under a vacuum, so it sucks oil from the lifter valley.

You have coolant passages in the intake manifold too, so you could be sucking coolant and that would make a white smoke (steam).

And why wouldn't you smell antifreeze when checking the coolant level?
Old 09-23-2008, 11:35 PM   #8
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Re: Bad intake gasket

I meant when driving I smell antifreeze. Inside the upper intake manifold there is a wet brownish black layer of something. Don't know if ifs oil or dirt and fuel mixed. The last time I drove it, I didn't notice any power loss or slow acceleration. So do you guys think that replacing the intake gasket will take care of the problem or should I be looking somewhere else?

Last edited by ace16a; 09-23-2008 at 11:40 PM.
Old 09-24-2008, 07:14 PM   #9
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Re: Bad intake gasket

Quote: Originally Posted by ace16a
I meant when driving I smell antifreeze. Inside the upper intake manifold there is a wet brownish black layer of something. Don't know if ifs oil or dirt and fuel mixed. The last time I drove it, I didn't notice any power loss or slow acceleration. So do you guys think that replacing the intake gasket will take care of the problem or should I be looking somewhere else?
Sounds like you are definitely getting coolant into the cylinders. It could be the intake manifold or it could also be a blown head gasket. I'd run a compression test to check the head gaskets before replacing the intake manifold gasket.
Old 09-24-2008, 09:00 PM   #10
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Re: Bad intake gasket?

Ok, so I started tearing into the motor a little further tonight and came across trany fluid in all the vaccum lines. Any ideas where the fluid would come from?It's definately trany fluid. And there is fresh oil all the way around the intake.
Old 09-24-2008, 10:26 PM   #11
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Re: Bad intake gasket?

Quote: Originally Posted by ace16a
Ok, so I started tearing into the motor a little further tonight and came across trany fluid in all the vaccum lines. Any ideas where the fluid would come from?It's definately trany fluid. And there is fresh oil all the way around the intake.

quick google:

http://www.chevytalk.org/fusionbb/sh...hp?tid/183007/

Quote: Originally Posted by txturbo
Check all vacuum operated controls on the transfer case and transmission.A bad rubber diapram in any of them will cause it to suck atf. I don't know what transmission you have, but on earlier models(70s and 80s) it was common for the rubber diapram in the vacuum modulator on the transmission to fail and it would suck transmission fluid into the intake.
Old 09-24-2008, 10:56 PM   #12
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Re: Bad intake gasket?

I can't get the link to work but in the quote, it says "70-80s" trucks. Is this still happening on vehicles after 20 to 30 years? You'd think gm would fix the problem. I guess I don't even know where to start looking. Am I going to have to get into the trany? Thanks for all the help and info so far.
Old 09-25-2008, 10:21 AM   #13
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Re: Bad intake gasket?

Quote: Originally Posted by ace16a
I can't get the link to work but in the quote, it says "70-80s" trucks. Is this still happening on vehicles after 20 to 30 years? You'd think gm would fix the problem. I guess I don't even know where to start looking. Am I going to have to get into the trany? Thanks for all the help and info so far.
GM hasn't used the vacuum modulator in its vehicles for a long time.

There are plenty of vacuum lines to the 4wd though. Here's a quote from Hamagc's post, above:

"It's probably because you are loosing fluid from the tranny to the t-case via a worn input seal or gasket (or both). This is a common problem. The seal and gasket will run you about $35. You'll need a light duty tranny jack or a helper to get teh transfer case off and on. Besides that it's pretty straightforward.

"To check, put the vehicle on level ground and check the t-case fluid level from the upper plug. If you pull the plug and a ton of fluid gushes out, that's the problem.

"There is an inlet in the top of the t-case that begins to suck the excess tranny fluid into the vacuum lines when there's too much in there. You'll need to flush ALL of the lines thoroughly and you might need to do the vacuum vent selector switch as well. It sucks, trust me. Let me know if that works out. "
Old 09-25-2008, 10:22 AM   #14
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Re: Bad intake gasket?

After removing the hood, I climbed ontop of the motor and saw puddles of oil on top of the intake. Can't tell where it came from. I also crawled underneith and traced the vacuum lines to the top of the transfer case. Am I going to have to drop it and take it apart to get at the switch?
Old 09-28-2008, 03:50 PM   #15
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Re: Bad intake gasket?

Anybody have a picture or an exploded view of the seal that is supposed to be replaced? Is it in the tranny or the transfer case. Got the trans pan removed and starting on the transfer case, just want to know what I'm looking for before starting. Once I get the seal replaced, what's a good way to clean the fluid out of the vacuum lines? Thanks

Last edited by ace16a; 09-28-2008 at 03:52 PM.
Old 09-29-2008, 04:26 PM   #16
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Re: Bad intake gasket?

Quote: Originally Posted by ace16a
Anybody have a picture or an exploded view of the seal that is supposed to be replaced? Is it in the tranny or the transfer case. Got the trans pan removed and starting on the transfer case, just want to know what I'm looking for before starting. Once I get the seal replaced, what's a good way to clean the fluid out of the vacuum lines? Thanks
According to the info posted above the leak is in the "worn input seal or gasket (or both)". The "input" seal would indicate that it is in the t-case.

I would blast the lines with compressed air to get most of the fluid out. Then I would flush the lines with a squirt of brake parts cleaner, and a final blast of compressed air to get it all out.
Old 09-29-2008, 04:59 PM   #17
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Re: Bad intake gasket?

Quote: Originally Posted by Yogi
According to the info posted above the leak is in the "worn input seal or gasket (or both)". The "input" seal would indicate that it is in the t-case.
Yup, it's in the t-case. You really don't even need to pull the tranny pan, just separate the transfer case from the tranny after you unplug all the vacuum lines and electrical connections from the t-case, and two driveshafts. Leave the transmission in the truck and just yank the t-case, and if yours was leaking as bad as mine was you won't even have that much transmission fluid come out of the back of the tranny once you pull it.

When you get the t-case out you will find that the seal is pressed onto the input shaft. I remember having a hard time getting that seal out, at the time I was working at a Ford dealer so I took the transfer case to work with me and one of the mechanic's popped it out for me. He also showed me a trick, and if I remember correctly what he did was he took a few bolts out and unbolted the front cover with the seal from the transfer case, and by doing that he was able to easily access the seal from the other side allowing him to easily tap the seal out rather than trying to pick and pry at it from outside the case.
Old 10-01-2008, 08:21 PM   #18
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Re: Bad intake gasket?

Thanks, been putting long hours in lately so I'll get to it tonight and tomorrow night.
Old 10-07-2008, 08:15 PM   #19
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Re: Bad intake gasket?

Ok, finally got the transfer case out and the front plate with the seal off. Definately the problem. Seal was hard like plastic and had crack going through it. I got a new seal, gasket, and vacuum modulator. There seems to be some kind of black silicone gasket under the plate, what should I use to reassemble and how much do I use? Thanks
Old 10-08-2008, 06:11 PM   #20
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Re: Bad intake gasket?

Never got to do that part of my repair myself, but if I was to guess I would say it is probably just black RTV silicone.
Old 10-12-2008, 08:58 PM   #21
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Re: Bad intake gasket?

Got everything back together and all seems to work like it should. Thanks for all the help everyone.
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