Rik O'Shay

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!

tombrammer

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)

John A. Marker

First check to be sure it is not the oil sensor (s) on the back of the block. If they go bad...you will lose a lot of oil very quickly.

Rik O'Shay

I will look at that,but, what I am I looking for/

A complete blow out from the block?

WW7

You can't retorque the intake bolts once the top end is assembled, you can't get to the bolts with a torque wrench once you get the runners and fuel rails on the motor.. This is a L98 , not an LT1 engine...Torque the bolts to spec and call it a day,or let the motor sit for a few hours and retorque the bolts again...One thing I will suggest, instead of using RTV sealant, use "The Right Stuff" on the china walls...This stuff is a rubberized sealant and sticks like glue to the china walls...Much more durable then RTV......WW

Rik O'Shay

The Right Stuff by Permatex, ok.

Rik O'Shay

Interesting advice that I found regarding the China Wall -

http://www.blowerworks.net/download/...china_wall.pdf

Cliff Harris

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.

John A. Marker

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.

Rik O'Shay

It was flowing out this morning when I checked, back of the block, driver's side.

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....

383vett

Just make sure it's not the valve cover gasket leaking before you go through to trouble of replacing the intake gasket.

WW7

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

Rik O'Shay

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.

John A. Marker

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.

leesvet

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

Rik O'Shay

I have a FSM and all of the addendums.

I'll go do what you said as the last thing I want to do is R&R the intake.

Rik O'Shay

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!

leesvet

Yw !

vl5150

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.