Lower intake leaking

chembrad · #1 02-01-2005, 03:55 PM

Well I replaced the lower intake gaskets on my '94 S15 Jimmy 4.3 V6 Vortec (W) and they were leaking at first. Now there is no external leaking, but my coolant gets black real fast. Exhaust fumes blowing into my coolant flow? Maybe.

Anyway, I need some specific advice on replacing the lower intake manifold gaskets correctly.

1. Do I need to use RTV on the gasket? I used it when I installed the gaskets the first time. I used Permatex High Temp Gray. A thin layer on both sides of the gasket, with a bead around all the coolant flow passages. I also ran a bead across the front and rear of the engine with a 1/2" up either side (then layered the gasket on the bead).
2. I used permatex white latex thread sealer on all the lower intake bolts (although only the front two and rear two go into the water jacket). My leak was through the front passenger side bolt, but it stopped about 24 hours later. Maybe when the thread sealer cured?
3. Speaking of curing, should you wait 24 hours after replacing the gasket before cranking the engine? I didn't, and it leaked a little for a day or so.
4. Any other tips/tricks that I missed to install the lower intake manifold correctly? I think I must have shifted the intake when I was installing it. That may have been my problem.

chembrad · #2 02-06-2005, 09:07 AM

Come on guys, help me out here. Certainly some of you fine folks have had experience with replacing lower intake and head gaskets??

BlazerLT · #3 02-08-2005, 02:55 AM

Did you torque them properly to spec?

chembrad · #4 02-08-2005, 01:46 PM

Yes I did with a rachet type torque wrench and then checked it with a standard lever type torque wrench. I didn't go back and retest them the next day though. I popped the rest of the engine back together and cranked it up. And it did leak around the front bolt at first, but then stopped as I said above.

Anyway, I am still going through and flushing the coolant each week. It is possible it was just all the crap that had accumulated in this engine that is the problem. I will know for certain as time goes by.

19 mpg btw. That is a definite improvement.

BlazerLT · #5 02-08-2005, 01:51 PM

You need to install a new gasket.

Having exhaust coming in the cooling system is a sign of a blown head gasket for sure.

chembrad · #6 02-09-2005, 03:13 PM

Well that is the way I am leaning. I'm just not in a hurry to do it all again...

BlazerLT · #7 02-09-2005, 03:27 PM

I thought you changed the intake gasket, but not the head gaskets?

Also, you need to find out which one is leaking.

94 Jimmy · #8 02-09-2005, 04:02 PM

Blazer, your right. Happened to me on my Olds minivan. I had the dealer replace the first one, stupid move. They were miffed when I wouldn't spring for a new engine and accidently left one of the head bolts finger tight. It lasted about 5K Mi until I was on vacation about 300 mi from home then started to leak.
I bought two tubes of AlumaSeal (I think they'er owned by Bars Leak now) and put it into the radiator. I warmed up the cooling system to pressurize it then shut it down to allow the aluminum flakes to form a plug in the head gasket, did this several times and it worked well enough to get me home where I could do a good job.
This has worked for me and others on several occasions to buy time for the weather to warm or to get home. On a couple occasions it was a permanent fix. The warm up cool down cycle is necessary because the pressures in the combustion chamber are a lot higher than the cooling system when running so any plug formed blows out immediately. However when the engine is stopped and the cooling system is pressurized to 15PSI the stop leak can do its thing. If after 5 or 6 heat/cool cycles it hasn't worked, then schedule a weekend and change the gasket. Also, depending on the milage think about having the valves ground and new guides installed while your there.
If you try the stop leak, let us know what happens, if it's not a head gasket, let us know also.
see ya 94

BlazerLT · #9 02-09-2005, 04:07 PM

I appreciate your fedback, but I don't recommend adding anything like that to a cooling system.

Will clog passageways that need the coolant more than the one place that it has to work.

chembrad · #10 02-14-2005, 07:21 AM

I added alumaseal or equivalent to my raddy once.

Then I had to change out the heater core as it was clogged tight by the crap. That is not an acceptable trade-off in my opinion.

Now I don't add anything to my coolant. And just fix the problems as they appear. I'm a much happier camper.

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