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New intake manifold and gasket looks wet and sweating?

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SirSpeedsAlot67

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1967 RS/SS Custom 350 SBC M21
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84 Posts
Discussion starter · #1 · (Edited)
Hey gents,

Been chasing a coolant leak issue at the front water ports on my built 350 sbc for a while now. I had went and tried a thicker SCE gasket #111139 that is .125'' thick (recommended by a local shop due to my heads being flat decked/milled from 64 to 60cc which i believe equats to about .0266' shaved off). So far, i have not seen any real signs of coolant leaks at the front or rear water passages. I tried pressure testing the system but found a bad o ring in the tstat housing that was slowing leaking so will have to replace that and test it agian to see if its finally holding pressure. Anyways, I now notice this gasket is absorbing coolant as it sits, you can visibly see it getting wetter. When i was pressure testing it, I also noticed a very small bead of water pop out (seen in pics). I have never noticed this with the fel pro 1205 gaskets I have used. I am wondering if I didnt rtv it correctly or if this is just normal? When it runs, it will obviously heat it up and dry the gasket out. I do not want coolant slowly seeping into the oil valleys as the car sits for extended periods. Should I re-do the gasket and put rtv around the edges of the gasket to prevent this? Or is there another better gasket I can use for this application? I applied a thin layer of rtv (right stuff) on the head and intake side, as well as both sides of the gasket and torqued it in sequence to 25ft lbs so i don't think i did anything wrong there. I also had the ports matched/ported and gasket cut for a good fit so the coolant port i know is lined up, i checked it with a scope to verify. I'm thinking maybe i need to also ensure i rtv the inner edges of the gasket that surround the water port? Or is this gasket junk? I emailed their tech support and they said it is a possible issue with the rtv.

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#3 ·
+ 1 on dry fitting the intake. If there is any rocking or gaps....it won't seal

The RTV shown in pics is a heavier bead than I use. Too much and the RTV squishes into valley....and into motor.

I have always used FelPro "printo" seal intake gaskets and Permatex Black Ultra on the front & rear. I have never applied any around head ports.

Thread sealer was used on intake bolts, right??
 
#5 ·
X2 on Socals post. I use the same and like him never any on the water ports on the heads, just the ends of the block. You can usually mill heads .006" before needing to mill the intake on standard SBC from what I have always read. I have had a lot of heards milled .005" and never any issues.
 
#6 ·
Need to also make sure gap is same at bottom of port and the top.
I had milled bbc heads once and when I measured the top was .015 wider gap then bottom. I had to angle cut the intake. I hope I am explaining this right. It’s possible to be tight but only on half the port.
 
Discussion starter · #7 ·
Hogdaddy said:
Too much RTV around water ports imho.
Click to expand...
SY1 said:
X2 on Socals post. I use the same and like him never any on the water ports on the heads, just the ends of the block. You can usually mill heads .006" before needing to mill the intake on standard SBC from what I have always read. I have had a lot of heards milled .005" and never any issues.
Click to expand...
I do think I may need to get the intake angle cut because I am on the third gasket and still having issues. I will have to try the next gasket with no port side rtv because i truly hate cleaning that crap off. I have dry fitted it before and it wasn't asymmetrical on both sides, but it seemed marginal to me. I had hoped a larger gasket and some rtv could potentially make it work. I do admit i put too much on the coolant ports, it squished way more than I expected. I had to use a heavy bead for the china walls because the gap was a bit over 1/8th of an inch. Sounds like i need to take this thing to the shop and see if they can machine the IM and straighten this thing out. Thanks!
 
#8 ·
SirSpeedsAlot67 said:
I do think I may need to get the intake angle cut because I am on the third gasket and still having issues. I will have to try the next gasket with no port side rtv because i truly hate cleaning that crap off. I have dry fitted it before and it wasn't asymmetrical on both sides, but it seemed marginal to me. I had hoped a larger gasket and some rtv could potentially make it work. I do admit i put too much on the coolant ports, it squished way more than I expected. I had to use a heavy bead for the china walls because the gap was a bit over 1/8th of an inch. Sounds like i need to take this thing to the shop and see if they can machine the IM and straighten this thing out. Thanks!
Click to expand...
Tighten manifold down slightly on one side. Then use feeler gauges, check it in front at bottom of port then the top. U don’t have get under it just from front at bottom then around top area both from front. The gap should be same if it’s bigger at bottom then the leak is the lower side or vise versa
 
Discussion starter · #13 ·
I am going to remove the IM one more time and check the mating surfaces without a gasket. If it looks ok, I am going to put on a fel-pro 1266 (assuming it fits right) and retry with a better RTV job. I tried pressure testing the coolant system again after fixing the water neck o ring, and while there were no leaks, the gasket got wetter and wetter and started to sweat. I believe the gasket is getting wet because there is not rtv around the edges of the gasket in the coolant ports. I am also thinking the SCE gasket is not a good quality as it is acting like a sponge, ive never had that problem with the printoseal gaskets.

I am going to use the 90 min right stuff this time because i felt the one minute stuff was drying too fast. Per the instructions, it states: "Assemble parts immediately while silicone is still wet. Finger tighten until material begins to squeeze out around flange. Let dry for one hour then tighten to torque specifications. ". Is this what the pros do for an IM gasket? Is there a better way of doing this? I have always just been torqing it down in sequence in multiple stages right away with the one minute gasket maker, but since the 90 min stuff drys slower, I want to make sure I am doing it right.
 
#14 ·
my $.02 was in post 3....but I didn't see your answer if you used "thread sealer" on IM bolts.

Again, I have always had good luck with permatex Black Ultra RTV on intake and pan gaskets. More because it is primarily designed for heat and oil. I do let it slightly cure for about 15 min on china walls, then install IM and TQ in sequence...THEN let it sit overnight before starting

Your coolant weep. to me, would be more coming through IM bolts if they also go into water passage. But an ill-fitting IM will never seal so if any machining needs to happen after you dry fit. do it.
 
Discussion starter · #15 ·
SoCal805 said:
my $.02 was in post 3....but I didn't see your answer if you used "thread sealer" on IM bolts.

Again, I have always had good luck with permatex Black Ultra RTV on intake and pan gaskets. More because it is primarily designed for heat and oil. I do let it slightly cure for about 15 min on china walls, then install IM and TQ in sequence...THEN let it sit overnight before starting

Your coolant weep. to me, would be more coming through IM bolts if they also go into water passage. But an ill-fitting IM will never seal so if any machining needs to happen after you dry fit. do it.
Click to expand...
Yes I put a PTFE sealant on all the bolts that go into the lifter valley. There are no bolts that go into the coolant area on these Profiler heads. May give the black ultra rtv a try, thanks!
 
#16 ·
SirSpeedsAlot67 said:
Yes I put a PTFE sealant on all the bolts that go into the lifter valley. There are no bolts that go into the coolant area on these Profiler heads. May give the black ultra rtv a try, thanks!
Click to expand...
You only need to run a 3/8 bead across front and back ( toss the rubber ones) into the tip of each intake gasket. The gaskets will take care of the rest. If you get the performance felpro gaskets you shouldn’t have a problem.
 
Discussion starter · #17 ·
Well I went ahead and replaced the gasket. Used a felpro 1266 that is .125” thick this time and it was a perfect fit, and seems like better quality than the SCE gasket. Did a better job on RTV an used the 90 minute right stuff and it cured nicely. So far no leaks on the pressure test so I’m hoping I’m going to be ok. When I dry fitted it, I could definitely see it was not sitting flush on the cylinder heads. I measured a .012” gap on the bottom edge of the intake manifold to cylinder head mating surface. The bolt holes also weren’t aligned but i figure that’s just because it’s not siting on a gasket. I might be lucky enough that the IM crushed the gasket in enough to compensate for the uneven mating surface. Time will tell. Thanks for all the help.

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SirSpeedsAlot67
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