BY: Ken, SLP Comp T/A #139
Recommended Practice For Repairing the Dreaded LT1 Intake Oil Leak
Some of us have had it, some of us have heard about it. I've had it, I had it 2 times on my 94 TA GT, 2 times on my wife's 95 Z28, and 3 times on my 97 Comp TA, in less than 1,000 miles!! So, being an Automotive Engineer by trade, having been involved with this "amusing" industry since 1973 in a professional capacity, I found myself in "the warranty thing ain't gettin' it" position and set out to find out what heck was going on. The dealer where I bought my Comp TA is a good friend of mine, so on the 3rd trip to the shop with the Comp because of the leak, I told him I was camping out with the car and this time "WE" were gonna fix it!
Well, WE found the problem. The EGR pipe...yep, that's right...there are two types, the solid and the flex. The flex is the more common...of course, I have the solid. The pipe does a 180 degree bend right down the back left side of the intake manifold heading for its final hook up. On long trips, the temp inside that pipe can reach upwards to 700 degrees Farenheit! Now folks, that's darn hot! The intake is torqued down with 35 ft. pounds a bolt...that's not much. The sealant is weak, we knew that. The liquid sealant is used in the front and rear instead of cork because of the "wavy-dippy" surface on the manifold. Bottom line: pipe gets hot, left rear corner of mainfold lifts ever so slightly, pressure under manifold is looking for a way out...finds its weakest link and carves a passageway...drip drip drip, right down the left rear of the block. The hotter the motor, the bigger the drip...the longer you wait for repair, the bigger the drip.
But...if it's not done right, it's coming back. For sure.
I would like to note before we start, at the Pontiac Nationals in 1997, I approached a GM Engineer for special programs about this. We ended up eating a hot dog together and having an upfront conversation. His words were "your right ..... off the record off course"...I won't relate the rest of the conversation in all due respect to him. So, for what it's worth...read on:
NOTE: This is a proven method of repair, literally hundreds of LT1's have been repaired using this method and the dreaded leak has not returned to haunt them.
1. First, if you have the flex type EGR pipe, push it as far away from the left rear corner of the intake as possible, but don't push it up against another component unless you want it fried!! If it's the solid pipe, there's nothing you can do but wrap it. I recommend wrapping them all anyway...an ounce of prevention....etc. Wrapping it: get some 1000 degree heat tape from your local speed shop. It has adhesive on one side and a reflective surface on the other. Wrap the pipe at the bend and a ways up and down where it is near the intake. Use a sufficient amount overlapping to insure a good insulation.
2. Next, after removal of the intake, check the rear of the manifold for ay discoloration on the left rear corner that would indicate excessive heat exposure. If you find it, it does no harm to have it there, it just "confirms" the culprit. Next.
3. Thoroughly inspect the mounting surface of the intake all the way around. Many of the intakes received bad casting and must be replaced. They will never give a good "seat" to prevent the leak.
4. Now, insure that the mating surfaces of the intake and engine are completely clean and dry. Use rubbing alchol...it even helps to slightly score the surface if you can...use a 100 grit wet sand paper...clean it up real good. Add the cork gasket to the sides and then apply the sealant on the front and back...a nice uniform rope type bead. We used almost a whole tube! No matter what that little tube says about "assemble right away", that stuff is just too runny to do that...let it sit for up to 20 minutes or so and "gel" slightly.
5. Put the intake back on, straight down! If you lay it on and slide it at all, you're going to end up pushing some sealant off.
6. Torque the bolts down from the inside out (most of us know that, well....we should anyway). And do it in 10 to 15 foot pound increments. Not the full 35 all at once!
7. After all is well and good, don't let anyone run the engine. That dern sealant tube says "to accelerate cure time, let engine idle for 15 minutes....NO NO NO!!! Let her sit for at least 24 hours to get a good cure before the engine is even started.
8. After a 1k miles, its a good idea to go back, following the tightening sequence, and re-torque the intake bolts.
9. As a final precaution, vent the crankcase to relieve some of that pressure. You can buy an inexpensive breather from L&G Motorsports, RK Sports, or any of those places. They come with a neck that screws into the valve cover where your oil fill cap is and then the neat little breather pops right on top of it.
Well, that's it....you're ready to rock 'n roll....no more gunky under carriage!