Mercruiser 3.7 Compression Question

[mannieg702]

Hi everyone hope someone can help out. I took my boat out this weekend and I notice that the coolant was vanishing, when I got to the dock I also noticed that the boat ran hot, till about 200 Degrees. When I go it home I checked it and there was basically no coolant in the tank. I did a lot of research and did a pressure test on the Cooling system, the Exhaust Gasket and the Riser gasket leaked under pressure. I already order those parts and will be replacing them. The HE seemed to be ok for now. I also followed the service bulletin that was posted by Don for the compression test. Here are the results Cyl 1. 180 psi, 2. 120psi, 3. 120psi and 4. 115psi. now here is the kicker when I was doing the test I notice that when I let the pressure out of the gauge there seemed to be Coolant spraying out of the hose. I have checked my oil pan oil and there is no oil coolant mixed there, there also appears to be no coolant on top of the Heads, could I still have a blown Head gasket? Thanks for any input.

 

[nola mike]

Re: Mercruiser 3.7 Compression Question

You're probably leaking coolant from the riser/exhaust gasket back into the exhaust manifold. Your #1 number seems suspect as well.

 

[cr2k]

Re: Mercruiser 3.7 Compression Question

It is possible to have a blown head gasket that does't involve an oil passage. So yes it is.

 

[Old Boat Luvr]

Re: Mercruiser 3.7 Compression Question

Your definately getting water in #1 somehow

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

Thanks guys, i will start engine disassembly this weekend to re place head gasket and have a valve job while i'm at it.

 

[nola mike]

Re: Mercruiser 3.7 Compression Question

Don't think you need to go that route quite yet. You know of at least 2 other sources for the leak which are consistent with your symptoms. It's possible that your overheat blew your HG, but I wouldn't assume that. If you ended up with a HG leak, you'd be out 2 gaskets and the time to replace them, which is maybe an hour (less if you don't have to drain the coolant!).

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

Don't think you need to go that route quite yet. You know of at least 2 other sources for the leak which are consistent with your symptoms. It's possible that your overheat blew your HG, but I wouldn't assume that. If you ended up with a HG leak, you'd be out 2 gaskets and the time to replace them, which is maybe an hour (less if you don't have to drain the coola

Would you suggest replacing the exhaust gasket and riser gasket first and re testing to see if waterr still shoots out the cyl.?

 

[nola mike]

Re: Mercruiser 3.7 Compression Question

That's what I'd do first. Make sure your mating surfaces are flat. I had troubles at the mani/riser gasket for a couple of seasons until I got the manifold surface machined over the winter.

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

That's what I'd do first. Make sure your mating surfaces are flat. I had troubles at the mani/riser gasket for a couple of seasons until I got the manifold surface machined over the winter.

Thanks I'll try that first.

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

I changed the exhaust and riser gaskets, and I'm I'm still loosing water some from some where. Re checked the compression and it all checked out however I still see to have coola coming out of cyl. # 1 and #4 my money is on the head gasket. Any thoughts?

 

[nola mike]

Re: Mercruiser 3.7 Compression Question

How old is the riser? Did you pressure test the system again?

 

[stonyloam]

Re: Mercruiser 3.7 Compression Question

Thanks guys, i will start engine disassembly this weekend to re place head gasket and have a valve job while i'm at it.

I believe you are at that point. Especially if you have coolant in #1. Some suggestions. Get a OEM Mercruiser headgasket, it is designed specifically for the 470. Keep track of the pushrods, they have to go back in the same holes they come out of. NAPA (Permatex) aviation sealant is a good substitute for Perfect seal. While you are having the head done have hardened exhaust valve seats put in. Make sure there is no fluid in headbolt holes when you put it back together. Good luck.

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

How old is the riser? Did you pressure test the system again?

did the system retest today and while it's not leaking at the riser and exhaust manifold any longer, the coolant started to come out the front of the motor between the head and the block. HG must of blown on when the engine ran hot, I'm not surprise as the boat sat for 3 years prior to last season when I bought it and got it back in the water, Thanks for your help.

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

I believe you are at that point. Especially if you have coolant in #1. Some suggestions. Get a OEM Mercruiser headgasket, it is designed specifically for the 470. Keep track of the pushrods, they have to go back in the same holes they come out of. NAPA (Permatex) aviation sealant is a good substitute for Perfect seal. While you are having the head done have hardened exhaust valve seats put in. Make sure there is no fluid in headbolt holes when you put it back together. Good luck.

Yes I believe so, Thanks for the advise, I will start on it on Sunday, found a shop in town that will mil,and do the valve job for 165.00 i will order the gasket this week. I have the Seloc Manual and been trying to find the one for my mercruiser #8 manual for my boat but haven't found it even for sale, I followed a link on the sticky but my wasn't able to view it on my pc either. Thanks

 

[stonyloam]

Re: Mercruiser 3.7 Compression Question

Here is the manual: I think you can print the pages you need: http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0 You will want to start on about page 67.

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

Here is the manual: I think you can print the pages you need: http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0 You will want to start on about page 67.

thanks the help is appreciated.

 

[nola mike]

Re: Mercruiser 3.7 Compression Question

did the system retest today and while it's not leaking at the riser and exhaust manifold any longer, the coolant started to come out the front of the motor between the head and the block. HG must of blown on when the engine ran hot, I'm not surprise as the boat sat for 3 years prior to last season when I bought it and got it back in the water, Thanks for your help.

Well, you got your answer now. Sorry that I cost you a few bucks in gaskets and probably an hour of your time :redface:

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

Well, you got your answer now. Sorry that I cost you a few bucks in gaskets and probably an hour of your time :redface:

no worries, with this things is a process of elimination. Just suck working on this thing when the weather is 100 degrees out here. I'd rather be at the lake. LOL, but i will fix it, They are fun so they are worth the pain. thanks for your input Boats are still a new venture for me. Car's are different story.

 

[mannieg702]

Re: Mercruiser 3.7 Compression Question

Happy to report that, The boat is back together and I took it for a test run on Sunday and she ran flawlessly. Thank you all for your input.

 

[stonyloam]

Re: Mercruiser 3.7 Compression Question

Great! Just one thing, (only asking because it is sometimes overlooked) did you retorque the headbolts after bringing it up to running temperature? According to the manual that is a very important step. Have fun.