Thread: LIM Gasket Replacement

LIM and VC bolts are 3/8" BTW. If you torque them with a 10mm you can round off the heads. Battery is an 8mm or 5/16". In many cases you'll find that the metric/standard sets are pretty interchangeable.

However.. on the LIM/VC's. I've found that I prefer a 3/8". As for the coolant elbow info.. I put these things together all the time and have no issues. Bulletproof, maybe not, but pretty darn good. Heck I changed one on Saturday.

As a tip, put some grease or something around the orings on the coolant elbows. It will help them from getting trashed when installing them so they don't leak.

I'm slowly working through these pictures to label and caption them. I will continually edit this post as I find pictures from my car, or pictures from the internet that may constitute a more complete "guide". Weather did not permit us to take our time so I could not make the complete walk-through that I would have liked. Whether you're a member of the forum, or you just ended up here somehow, hopefully this thread will inspire you to maintain your engine.

Alright, lets begin.
By time we started taking pictures we had already unplugged the Mass Air Flow sensor, Idle Air Control (Valve), and Throttle Position sensors on the throttle body. Remember that the Throttle Position Sensor is spring loaded so when you put it back in you will have to "wind" it as much as a quarter inch. Also, we unplugged the Intake Air Temperature (IAT) sensor (in the large diameter black ribbed tubing connecting the air box/filter to the throttle body), and the Manifold Absolute Pressure sensor (MAP). The MAP sensor is on the passenger side of the plastic Upper Intake Plenum and sits directly above the metal PCV (positive crankcase ventilation) valve. I check the metal PCV valve with every oil change. Once you pull off the MAP sensor the metal PCV valve is directly underneath, snugly secured inside the plenum by its own o-ring. I pop it out by hand, hold it next to my ear, and shake it to hear the "click/clack". If you shake the PCV valve and it DOES NOT "click/clack", the PCV valve is not working correctly and needs to be replaced. The MAP sensor (when removed from it's plastic housing) has a small ribbed rubber grommet attached. I replaced that with this job.

1.
Here's the engine after taking off the front mounts, alternator, air intake with the air filter, and several vacuum hoses that go from the back of the engine to such things as the evap canister, a few solenoids, the fuel pressure regulator, the throttle body, and one to the transmission. We also removed the fuel injectors. At this point it would have been wise to plug the fuel injector bores with towels of some sort because of the incredible amount of dirt and debris stacked up on top of the LIM. Remember that those small holes lead straight into the heads and the last thing you want to do is cram dirt into there.


2.
After removing the alternator and the alternator bracket from the passenger side of the engine, we took this picture to show one of the leaking plastic coolant elbows as well as the bottom of the LIM where it meets the block/side of the heads. There's an abundance of moisture here from both the leaking UIM and the leaking LIM gaskets as well.



3.
This is the same area as picture #2, closer. Notice that its not just dirt in there, there are bugs, bits of gravel, and gobs of old RTV silicone waiting to fall into your engine once you crack it open. More importantly though, look at the failing end-seal caked with oil and debris. The leaks from the UIM seeped down to mix with the leaks from the LIM and coolant elbow, so in this case there's a big mess of oily coolant and everything wants to stick to that crap. Get it off of there if you can.


4.
We popped off the UIM, you are looking at the EGR stovepipe passage flanked by two coolant passages. This may look benign at first glance, but the EGR passage having gotten so hot for the entire life of this part makes it easy for the o-rings around the "death-cool" passages to wear out and leak. (notice the dirt working it's way inward on the failing coolant passage o-ring on the left.


5.
Again, same area: the EGR stove-pipe passage next to the two coolant passages on the UIM. Here you can see how dirt was nearly entering the coolant passages. I'm no engineer so I don't know at what point it would have given out, but I can guarantee you that replacing my UIM was NOT a waste of money.


6.
Here is the top of the LIM after we popped it off. At first glance, not too bad... right...?


7.
That green looking liquid in the center of the LIM defies my imagination. I bought this car with orange dex-cool in it. Then I paid to have the old stuff replaced with new dex-cool. It wasn't "flushed" by me, merely replaced. But, whether it be a mix of old green coolant, new dexcool, or oil, that crap is green... There's better evidence in a later picture of one of the water jackets.


8.
If you are reading this thread, you need no introduction to the engineering-disaster that is the LIM gasket set on my Series II 3800. Just pay attention to the water passages, all 4 of them are destroyed. Also, a few of the passages between the intake runners and the LIM were starting to fail. Excellent...


9.
FAIL


10
FAIL


11.
FAIL


12.
FAIL


13.
Etc, etc, etc...


14.
Here's what these suckers looked like before we took them out of the engine. Remember to keep all that crap on the LIM from falling into the engine. Put some shop rags in the lifter valley.


15.
Now, in another stroke of pure-genius, GM only built the LIM with one complete coolant passage between 2 of the 4 water passages designed into the LIM gaskets themselves. The result: the 2 other ports or "water jackets" in the heads (which are accounted for by the LIM gaskets but do not get connected via the LIM) do absolutely nothing to aid in circulating coolant. The spots where the coolant backed up against the LIM is moderately pitted/eroded.


16.
Here's one of the cleaner water passage.


17.
It's not peanut butter...


18.
Again, evidence of green/yellow coolant. Really no idea what else that could be...


19.
Milkshake. Bad, bad milkshake.


20.
One of the valve covers open, before we wiped both of their contents out.


21.
The cleaning process for the LIM consisted of 12 hours of soaking in brake cleaner/engine bright/ hot water inside a clean plastic trash can along with the throttle body, then 2 hours of scrubbing in my sink with a toothbrush, a wire brush, and more brake cleaner. Here it is after we re-installed it onto the engine and installed the fuel injectors with both new upper and new lower o-rings.


22.
The newly cleaned LIM installed back on the engine and plugged with paper towels. (right before injectors)


23.
Looks way better huh?


24.
To install the new smaller diameter EGR stovepipe I used a close fitting socket (can't remember what size) and tapped the socket very gently with a small hammer. What you should really pay attention to in this picture is the slight pitting around the EGR stove-pipe passage and the two coolant passages caused by intense heat and leaking coolant. What I would like to post later on if possible is a picture of one of the points on the LIM where the hot, pressurized coolant gathers in the water passage and backs up against the LIM. At that spot on the LIM, the coolant (filled with particulates, pieces of gasket, RTV, sand, and whatever else leaked into the coolant) ate through the LIM for about 1/16". We're talking deep pits eaten into the metal.


25.
Until I load the rest of the more random pics, here's one of the bore for the Idle Air Control valve on the throttle body. This was the only point of the TB that was this filthy. Months ago I had to take out the IAC valve and scrape most of the hardened carbon/dust out of the valve bore because it got stuck shut. This led to a terribly low idle and may have burned out the "worm drive" or "stepping motor" that controls the opening and closing of the pintle. Until I put a new IAC in I won't know for sure whether the one I have is burned out or not.

from the look, those LIM gaskets are plastic, i'm not sure..

fel-pro is what you wanna buy.

Originally Posted by KZOO3800

I'd recommend all the parts in post #14 that I listed in the first page of this thread to solve the EGR heat issue AND the LIM failure issue. Then all you'll need is an EGR valve gasket and the rectangular gasket for the small cover on the side of the LIM.

It'll cost more but replacing the original plenum is a good idea, especially if your car has high mileage.

AGAIN HE SAY, replace your plenum!

Unless you want your LIM and coolant cylinders to look like THIS, then replace your plenum so that it doesn't fail and hydrolock your car, only to spin a bearing 1000 miles later.

The bigger problem isn't the DexCool, as it is the gasket material choices. Anyone that has looked at the plastic gaskets in detail will notice they always are bowed/cracked in the center of the edge of the coolant ports. Usually worse on the back than the front head.

My theories on this are simple. Nylastic is not the best material and I read an article on that exact item being the largest issue. I proved out that they bow on fresh non-Dex coolant in less than 40K miles in my own engine. The heat seems to be the larger issue for the gasket degrading and bowing. Then the seal has nothing to hold it in place. Coolant can leak, get to air, turn acidic.. poof. Also there are relief cuts in the plastic gaskets, they appear to be for expansion. That's where they crack.

I didn't have it done at the time of this original post, but I'd recommend looking over the How to mod an LIM thread. I like to think it addresses some rear head flow/heat issues and plugging the coolant ports, so that there's never a chance for the EGR stove pipe to crack the UIM and allow cooalnt into the intake.

This is next on the to do list.
Sub'd