slhawkins

I just finished swapping out the intake manifold and was a bit shocked to see coolant flying out of my exhaust when I started it up. I thought that maybe the coolant just leaked into the combustion chambers while removing the intake so I let it idle for a little while and before I knew it I had a trail of coolant under my car. I assume this means I've got a head gasket issue, but since I didn't have this problem before I wanted to verify how likely that was before I started tearing into it again. Thoughts?

antfarmer2

Sound like a plan. Better pull the plugs and get the coolant out before you hydrolock it or rust it up.

confab

Your oil good?

slhawkins

I'm not entirely certain. The oil is nearly its end of life and it feels a little thin, but there isn't any separation of liquids on the dip stick. It may be there I haven't run it enough for there to be a bunch of coolant in the oil or I simply haven't given it enough time to separate. I'll check again this evening or tomorrow morning.

slhawkins

Are there any other reasons this problem might occur after an intake manifold swap?

I plan on putting some dye into the coolant and running it for a little while. I'm certain I'll see the dye coming out of the exhaust - but I'll be interested to see what I find in the intake manifold. Once I yank the runners I plan on checking for the dye.

*I could also use this to check whether there is coolant in my oil.

confab

I'm not familiar with the other engines, but I know on the L98, if you saw that? There really wouldn't be a need to diagnose it further.

Just tear it apart and check the intake gasket. But that seems unlikely.

Leaving the head gasket or a cracked cylinder head.

confab

Is the coolant trail on the floor coming from the exhaust? Or possibly leaking from the rear passage, down the head, and onto the floor?

I mean, are you sure it is constantly blowing coolant out of the exhaust?

slhawkins

Coming out of the exhaust at two places - an exhaust leak on the passenger side where the manifold and down pipe meet (on the list for fixing) and at the exhaust tips. I pulled the car out of the garage and the driveway is at a slight slope. So much coolant came out in under 5 minutes of idling that the entire driveway under the Corvette is soaked. :-( Luckily I was draining the coolant out and have mostly water in it at this point.

confab

Others may disagree, but I think that's it.

It's time to just take it apart and see.

stanleyz

I installed new injectors a while back and it seems to me there is a coolant passage through the intake or maybe two. You didn't blow a HG or crack a block by removing and reinstalling the manifold. You missed a gasket somewhere or missed sealing at the corners. Tear it down slowly and you will find the leak. Most likely one of those passages.

slhawkins

I was hoping that was the case, and I think I figured it out.

I was going to put this off for two weeks since between college exams and full time work I have very little free time to spend with the wife - but since it was all fresh in my head I decided to grab some dye and yank it apart. Now that I've done that I feel like I wasted some of your guys time, so please know that I appreciate the help!




Intake manifold - cylinders 6 and 8.



Cylinders 6 and 8 are getting the coolant...





Gasket was soaked, when I originally took it off I mentioned to the wife that I was sure I put the new one on. I came back to it later and realized it was just soaked.




I'm not sure if you can make it out, but the lower bolt hole to the 6/8 runner pair is exposed to the rear coolant passage.

I checked the original intake manifold and the same 6/8 lower runner bolt hole is not exposed to the coolant passage. The manifold pictured above is an Accel 74197 intake manifold. I'm not sure why the bolt hole would be exposed to the coolant passage, nor am I sure if it was meant to be this way. Would you guys just throw some thread sealant on it and call it a day?

Thanks for the help!

confab

Yeah, I probably would. I've seen it done a lot in situations like this.

Be careful with silicone and other sealants in a blind hole. Believe it or not, you CAN compress that stuff tightly enough to cause a casting fracture. (I know this because I missed some in a ZF unit once and blew the back of the case out when I tightened it up. Whoops!!!)

Glad it is an easy fix for you and doesn't involve the heads or anything like that!

You'll be back vettin' in no time!

W@@T!

VikingTrad3r

i used permatex aviation form a gasket for my heads. works great, no oproblems.

ddahlgren

+1 great stuff works well on radiator and heater hoses too though you will hate yourself later taking them off but never leak either.

slhawkins

So it's still doing it. :-(

This time, I decided to go even slower at taking it apart. Looking back through my photos I remembered that I had seen the coolant dye in the 9th fuel injector hole and coolant on top of the intake valves of the head for cylinders 6 and 8. So I'm pretty sure it's the intake.

So I yanked the 9th injector cover (I remove the injector itself) and looked for coolant. Nothing, so I popped the radiator cap and started filling it up to the top. I immediately noticed a sound and put a hose up against the 9th injector hole while the wife filled it up more. The sound was definitely coming from that hole. So I kept filling it up and soon saw coolant puddling up into that hole. Next, I popped the rear coolant line that goes over towards the heater core and put a little air into it. The radiator overflowed a slight bit and the coolant in the 9th injector hole moved.

Any ideas? I assume no one has a CAD model of the intake manifold, so unless this sounds familiar I'm going to give Accel a call on Monday and have a nice chat with them. Hopefully they can pinpoint while coolant is in there.

stanleyz

OK, I was looking at your pictures and I think I remember something. In looking at the heads on the front of the engine there are two passages where coolant goes through the intake and across to the other head. If you look at the rear of the heads you will see that there is a passage on the drivers side but nothing on the passenger side. Check and make sure your manifold gasket on the passenger side blocks off that passage. if I recall this right, there are two different gaskets, one set has the block off for the rear passage and one is open there for motors that use the rear passage. Now, if that's completely wrong just ignore it but I seem to recall reading that when I installed my injectors.

confab

Agree.. It has to be a messed up gasket issue somewhere.

What else would cause that?

stanleyz

OK, I went out and re-read my FSM this morning. This applies to my 87 with L98 and I'm not sure what your car is so it may be different for your car. What is says is that the "blocked ends of the intake gaskets go to the rear". I think what I remember is that there are other small block manifold gaskets that DO NOT have the rear passages blocked. So, perhaps you have a gasket that don't block the rear passages or you installed them with the blocked ends to the front. Or maybe it's none of the above.

Also, these are aluminum heads, if it's not gaskets check carefully for a small nick near one of the passages. It wouldn't take much to allow coolant to go through. Hope you find this helpful.

JrRifleCoach

Yes. Coolant travels across the intake from heat to head.
Get a good Felpro gasket set and lightly coat the head to intake gaskets with BLUE silicon sealer. Then ensure the manifold is square and seated before you start dropping bolts. All the bolts should easily engage their threads. Then torque according to the FSM.

A job best suited to not rush.....

slhawkins

I have an 87 with an L98 as well, so this applies to mine. By "blocked", does it mean that it's entirely blocked off or just has a restricted opening? The gaskets I got have a small ~1/8" hole that allows coolant to pass through it and into the rear of the manifold. I expect this is correct since there is a small coolant hose off the back of the manifold that goes to the heater core.

I called Accel and they had nothing to say about it, no idea why it would do it but also no idea what to check.

I'm going to take it back off later this week and feed water into the 9th injector hole, see where it comes out.