View Full Version : Intake manifold question

09-20-2008, 03:04 AM
I just bought my first mastercraft. A 79 with a 302 ford in place of the 351. The story is the previous owner cracked the block of the 351 by leaving water in it over winter. He picked up a 2 barrel 302 marine engine and installed it..........then wanted more hp, so he bought a 4 barrel intake from Summit, and now it leaks water into the oil. Is there a difference between a marine intake and the non-marine intake he bought, or did he just screw up th intake gasket?

09-20-2008, 03:46 AM
Can't see how changing the carb would cause water to get into the oil.

09-20-2008, 04:01 AM
No difference as far as I can tell. Most likely messed up the gasket.

09-20-2008, 05:57 AM
.. and I would bet the biggest reason for lack of grunt isn't the carb but the cam. If he just dropped a mustang engine in it I would check the starter and carbs to make sure they are both for marine use before she blows... and then the cam. The desired HP curve isn't the same on a car and boat and you will fight low end power until you correct it.

09-20-2008, 07:31 AM
I think he did put in a marine engine..........

09-20-2008, 09:14 AM
Yes it is a marine engine, and perhaps I wasn't clear enough with my question. When the previous owner changed the intake and carb is when he started having problems with water in the oil pan. My first thought was that there was a difference between a marine intake manifold and an automotive intake manifold where there might be different cooling passages that didn't line up properly. I guess I should get the answer when I take it apart today.

09-20-2008, 09:53 AM
"He picked up a 2 barrel 302 marine engine and installed it"

I think that pretty much said it.

Yes, there can be some differences between marine and auto gaskets but if the manifold is made for a Ford, the cooling passages should be right. Sometimes, there's a block-off or a reducer but that will affect the cooling and shouldn't make it leak into the oil.

If he only changed the intake and carb, look for evidence of gasket sealant at the edges, along the heads. The only place that gets that kind of sealant is at the front and back, where it's not a high pressure area. The gasket failed, IMO.

How much water is getting into the oil? Is it only slightly milky or is it like a milk shake? If it's the latter, it may need to be torn down, especially if it has been run this way for any length of time and/or run hard.

I don't know why he replaced the 351 with a 302. First off, it won't be as powerful and second, replacing the intake won't make up the difference. It might add a little low end but ultimately, it's not the right way to go about it.

I'd be talking to the previous owner about this.

09-20-2008, 10:57 AM
Sounds like a gasket issue. Confirm that you have EGR or non-EGR heads and make sure the intake matches up. I don't think you would get water in the oil from not matching them up, but it may cause issues.

I would also suggest that the 302 would provide enough torque/HP if setup right. after all, it's a 19' boat ...

09-20-2008, 12:18 PM
The only difference between a marine intake and an auto intake (in this specific case) is that marine intakes are normally coated to resist corrosion. There is a very good chance that the gaskets are leaking. It only takes an hour or two to change it out, plus you already have water in your oil, so that needs to be changed also. The only other thing may be if the block or intake is warped. Not knowing the whole story of the boat, no way to tell.

09-20-2008, 08:57 PM
Got the intake off and the gaskets look ok - no noticable sign of a leak, and everything appears to match up. I did find a Mercury tag on the block. Don't know if that makes any difference. I spoke with the previous owner again, and he confirmed that there wasn't any water in the oil issues before he changed intakes (incidently, it is a new intake friom Summit). The only thing that comes to mind is that I don't think he properly torqued the intake bolts, as some of them seemed just snug and not torqued to spec. Don't know if thats enough to create a leak. Time to check with a Mercury guy to see if there is any difference. If not I suppose I need to do a compression check and look for a crack. Any other ideas? I appreciate the input.

09-20-2008, 09:07 PM
Were the gaskets stuck to the intake manifold or the heads? If the gaskets had a fine line of what looks like sealant that had dried, it's supposed to bond when the motor gets to normal operating temperature.

If the bolts weren't torqued to spec, it can easily cause the leaking. Look for any evidence of cracking on the intake manifold and the heads, where the manifold mates with them.

IIRC, the bolts are torqued to 35 ft-lb, starting at the center pair and then criss-crossing until they're all tight. DO NOT use a beam type torque wrench. Beg or borrow a good clicker type that hasn't been dropped, used to break up concrete, etc. Ideally, it should have been calibrated fairly recently but if it's in good shape, that may not be a deal breaker.

09-20-2008, 11:56 PM
Gaskets were stuck to the heads, and they looked new except where I boogered them up when I used a screwdriver to pop the intake loose. I will have to do some more careful checking in the morning.

09-21-2008, 11:02 PM
also a possibility of blown head gasket. That is a big way to get water into the oil. Like another said, how much water is in the oil. Is it 5 qts overfull, or just a little condensation?

09-23-2008, 09:55 AM
I got the oil out and it only has about half a quart of water mixed in. The last owner only ran it four times for about two minutes each. He wasn't sure if he torqued the intake manifold, so I may get lucky and find that is the only problem. Time to go back together and test run it. I still don't hane a good answer if the Summit 4 barrel automotive intake will work on here or not. Any ideas?

09-23-2008, 10:04 AM
Call Summit. They may have photos of what you need to look for and can either e-mail or fax them to you.

When you buy new gaskets, specify that you need the ones for marine application. A good parts store will know that they can get them and if they don't know this, they'll ask what the difference is or look at you like a dog watching TV.

Also, after everything is in place, bolts are tight and the end seals have cured (don't crank it until the sealant on the end seals has cured), do a vacuum test.

10-10-2008, 01:33 AM
Finally got the time to get the job done. The intake gaskets were correct and apperantly the previous owner failed to properly torque the intake. Had it runnung for a while today with no problems. Thanks to all who offered assistance.