Blown Intake Gasket?
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Blown Intake Gasket?
1991 C4
L98, no mods, 62,000 miles
So it looks like an intake gasket on the left side of the engine just blew, spewing oil out of the rear of the manifold,dripping on the exhaust & smoking out the area
So I know that I'll be replacing the gaskets but here are my new owner questions -
Any concerns?
Any inside tech advice for the job?
Specific manufacturer of gaskets recommended?
Thanks!
L98, no mods, 62,000 miles
So it looks like an intake gasket on the left side of the engine just blew, spewing oil out of the rear of the manifold,dripping on the exhaust & smoking out the area
So I know that I'll be replacing the gaskets but here are my new owner questions -
Any concerns?
Any inside tech advice for the job?
Specific manufacturer of gaskets recommended?
Thanks!
Last edited by Rik O'Shay; Sep 15, 2014 at 05:09 PM.
Pro
Joined: May 2008
Posts: 670
Likes: 55
A common problem on these motors, the seal around the oil sending unit is very thin and often blows out. Don't use the china wall gaskets (I don't think the intake gasket kit for these cars even includes them) instead use a good RTV silicone sealant. Don't forget to re-torque your intake bolts at least 4 times after your warm the motor up (re-torque drive a couple of days then re-torque 3-4 times or until they won't tighten any more)
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
A common problem on these motors, the seal around the oil sending unit is very thin and often blows out. Don't use the china wall gaskets (I don't think the intake gasket kit for these cars even includes them) instead use a good RTV silicone sealant. Don't forget to re-torque your intake bolts at least 4 times after your warm the motor up (re-torque drive a couple of days then re-torque 3-4 times or until they won't tighten any more)
....WW
Last edited by WW7; Sep 15, 2014 at 09:30 PM.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Interesting advice that I found regarding the China Wall -
http://www.blowerworks.net/download/...china_wall.pdf
http://www.blowerworks.net/download/...china_wall.pdf
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The key phrase in those instructions is, "Use a high quality silicone sealant and lay down a very thick bead at the front and rear block rib." The silicone should end up looking sorta like this: O-----O. It should bulge out at the front and back of the China wall. That prevents it from moving and leaking. This is what mine looked like when I took it apart recently:
The most common reason for using The Right Stuff is that it cures much faster than RTV. It's not necessarily better at sealing.
The most common reason for using The Right Stuff is that it cures much faster than RTV. It's not necessarily better at sealing.
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Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Start the car up and watch the rear of the block under the car. If the oil comes streaming down the side or rear of the block and forms a puddle on the floor it is NOT the china wall seal. The sending units will stream more than you would think possible.
The china wall leak will be slow.
The china wall leak will be slow.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Start the car up and watch the rear of the block under the car. If the oil comes streaming down the side or rear of the block and forms a puddle on the floor it is NOT the china wall seal. The sending units will stream more than you would think possible.
The china wall leak will be slow.
The china wall leak will be slow.
I couldn't tell exactly where the oil was coming from but it didn't look like it was coming from the one sensor that I could see.
Also, there is some oil on top of the intake manifold, driver's side, all the way to the rear.
And the previous owner had this gasket replaced by "Brakes Plus" of all people, so you know that it was done right...
So I'm planning on pulling the manifold, cleaning it up, porting it (and the runners & plenum) some and then installing new gaskets/china wall the right way with the Right Stuff-
I'll take a bunch of pics & post them up....
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
If you have oil on the top of the manifold it may not be the rear china wall leaking , since oil won't run up hill.. I'm thinking maybe it sprayed up there from either the sending unit, or like Willie said, maybe from the valve cover....
.I'd be pissed if I went to all the trouble of replacing the intake gasket only to find out it was something simple...
..Now, if you want to pull the intake to port match everything , that's another story entirely.....WW
Last edited by WW7; Sep 16, 2014 at 07:52 PM.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
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From: Denver Colorado
I just gave it a good look and don't have any oil at the rear of the left head/below the valve cover.
It seems to be leaking from the center of the engine maybe off to the drivers side a bit. It was flowing out with the engine rinnine, not spraying- but I didn't rev it up either.
It seems to be leaking from the center of the engine maybe off to the drivers side a bit. It was flowing out with the engine rinnine, not spraying- but I didn't rev it up either.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
The oil sending unit is toward the driver's side of the block rear. So if you have oil running down the rear of the block and up on the intake, chance is that it is the oil sending unit/sensor.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Do yourself a big favor and start the process of getting TO the OIL pressure sender and oil pressure switch.
Your leak is there OR the "tree" that the 2 sensors are mounted on. You are able to see the oil pressure sensor IIRC...the switch is below that.
remove the wiper motor. Pull wire harness GENTLY aside and wash area down with spray on degreaser and water hose...or wipe it down with rags IF you can get to it.
start engine and observe the leak.
WHY?
intake gaskets don't "let go" and spew oil like that.
Valve cover gaskets don't have any pressure behind them so they ooze oil...not spray or puddle.
Oil pressure sender./switch at the rear of driver side head is known to "spray" oil since it IS under pressure...duh...oil Pressure sender.
Be careful with the "T" or "tree" as it strips very easily. use Teflon tape on the threads or liquid Teflon to seal it.
A FSM would be helpful. They sell currently on E-Bay used for $50 for both books. Information does not come any cheaper than that !
have fun
Your leak is there OR the "tree" that the 2 sensors are mounted on. You are able to see the oil pressure sensor IIRC...the switch is below that.
remove the wiper motor. Pull wire harness GENTLY aside and wash area down with spray on degreaser and water hose...or wipe it down with rags IF you can get to it.
start engine and observe the leak.
WHY?
intake gaskets don't "let go" and spew oil like that.
Valve cover gaskets don't have any pressure behind them so they ooze oil...not spray or puddle.
Oil pressure sender./switch at the rear of driver side head is known to "spray" oil since it IS under pressure...duh...oil Pressure sender.
Be careful with the "T" or "tree" as it strips very easily. use Teflon tape on the threads or liquid Teflon to seal it.
A FSM would be helpful. They sell currently on E-Bay used for $50 for both books. Information does not come any cheaper than that !
have fun
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
Do yourself a big favor and start the process of getting TO the OIL pressure sender and oil pressure switch.
Your leak is there OR the "tree" that the 2 sensors are mounted on. You are able to see the oil pressure sensor IIRC...the switch is below that.
remove the wiper motor. Pull wire harness GENTLY aside and wash area down with spray on degreaser and water hose...or wipe it down with rags IF you can get to it.
start engine and observe the leak.
WHY?
intake gaskets don't "let go" and spew oil like that.
Valve cover gaskets don't have any pressure behind them so they ooze oil...not spray or puddle.
Oil pressure sender./switch at the rear of driver side head is known to "spray" oil since it IS under pressure...duh...oil Pressure sender.
Be careful with the "T" or "tree" as it strips very easily. use Teflon tape on the threads or liquid Teflon to seal it.
A FSM would be helpful. They sell currently on E-Bay used for $50 for both books. Information does not come any cheaper than that !
have fun
Your leak is there OR the "tree" that the 2 sensors are mounted on. You are able to see the oil pressure sensor IIRC...the switch is below that.
remove the wiper motor. Pull wire harness GENTLY aside and wash area down with spray on degreaser and water hose...or wipe it down with rags IF you can get to it.
start engine and observe the leak.
WHY?
intake gaskets don't "let go" and spew oil like that.
Valve cover gaskets don't have any pressure behind them so they ooze oil...not spray or puddle.
Oil pressure sender./switch at the rear of driver side head is known to "spray" oil since it IS under pressure...duh...oil Pressure sender.
Be careful with the "T" or "tree" as it strips very easily. use Teflon tape on the threads or liquid Teflon to seal it.
A FSM would be helpful. They sell currently on E-Bay used for $50 for both books. Information does not come any cheaper than that !
have fun
I'll go do what you said as the last thing I want to do is R&R the intake.
Thread Starter
Instructor
Joined: Aug 2014
Posts: 173
Likes: 9
From: Denver Colorado
It was just the oil pressure switch, oil coming right out of the connector-
So tomorrow I'll return all of the stuff I bought in preparation of an intake manifold gasget change & raise a beer to you guys for helping me out!
Racer
Joined: Jun 2013
Posts: 341
Likes: 2
You lucked out so my advise is to buy a lottery ticket. I just had to re-do my intake as I had a RTV blow out on the china wall near the oil pressure sender. Not a hard job, but not exactly a fun thing to do once let alone twice.