Mariner 175 overheating problems......

[dclange]

Mariner 175 V-6 1987

This motor alarms shortly after opening it up and getting on plane. At idle it is fine. This is what I've done so far. New water pump (whole thing), new stats, new temp sensor, new poppet valve parts. Did a compression test with warm motor. #1-104, #2-106, #3-115, #4-116, #5-123, #6-100. As you can see #6 is a little low. Are these compression numbers out of line for this old of a motor? I also run some test in the drive way on the muffs. Start the motor and let idle. After right at 3 minutes stats open and good stream of water. Water temp right at 143 when stats open. Something else I tried. Took the poppet valve parts and cover completly off motor. Started the motor and let idle. To my surprise, blue smoke/exhaust came out of the poppet hole in the block for the first few seconds (maybe 5 seconds) and then the water started pouring out. Shut it down. Tried it again a few minutes later, same thing with the exhaust, then the water. My main question, is should their be exhaust in the water jacket like that? And if not, what does that mean? Thanks for everyones help.....Dave

 

[dclange]

Re: Mariner 175 overheating problems......

Anyone have any ideas or thoughts on this problem?

 

[j_martin]

Re: Mariner 175 overheating problems......

Head gaskets, cracked exhaust divider plate among other things.

What do you mean by poppet hole? The poppet is a valve, and shouldn't vent anything to the outside.

hope it helps
John

 

[CharlieB]

Re: Mariner 175 overheating problems......

There are two things that you haven't checked, The exhaust plate and the lower exhaust adaptor plate. I'd bet on the lower exhaust adaptor plate gasket split and as RPM/loads rise, the exhaust pressure leaks into the cooling water passage causing engine heating at upper RPM.

You are goiong to have to lift the powerhead off the mid, clean the surfaces and replace the gasket.

I am a little concerned that the cyl compression is getting low and inconsistent. You may consider re-ringing all pistons over the next winter.

 

[dclange]

Re: Mariner 175 overheating problems......

j_martin, What I mean by poppet hole is the hole where the poppet valve normally sits in. I had the poppet valve, spring, cover, everything, off of the motor. With it all off, I started the motor on the muffs in the driveway. I'll try to explain better. Picture this, the motor is off, garden hose running water, the hole where the poppet valve seats in the block is empty, I can see inside of the block or water jacket. So, no water is inside of the main block of the motor at this time, it is empty. I just thought I would try this test to see what would happen. I wanted to see how long it would take the water pump to start filling the block with water, to see if the pump was working good. So I started the motor with the poppet valve off the motor.
To my surprise, blue smoke comes out of the poppet hole like a exhaust pipe, until the water finally starts to run out the poppet hole. Hope this explaination helps.

CharlieB, I'm right down the road in Marthasville, .
You said you would bet on a split adapter plate gasket leaking exhaust as the rpm/load rises. When I do this test, I'm just starting the motor and letting it idle in neutral, no load, no high rpm's, and the exhaust is comeing out as soon as I start it up. Would or can this gasket be leaking exhaust just at idle? My point being that as soon as you start the motor, it is pumping exhaust out that poppet hole like a small exhaust pipe, until the water starts coming out. Would this adapter gasket leak that much exhaust that fast, say more so then a head gasket?

I'm going to have to do some more homework on what your talking about, parts etc. I'm not to sharp on 2-cycle motors, or out boards. Cars yes, use to drag race, rebuild motors, etc. Get back with you guy's later.......Thanks for all of the info..........Dave

 

[CharlieB]

Re: Mariner 175 overheating problems......

Have your serial; # and go here

http://www.mercruiserparts.com/SelectModelType3.asp?class_id=2

Once you find your serial range, look at

Exhaust manifold and plate, item (?) 26, the adapter plate under the motor. The water passage and exhaust passage are right next to each other, when this part of the gasket fails then exhaust immediately leaks into the cooling system.

Yes, you will get exhaust gases and smoke out the poppet until the water fills the void and obscures the exhaust. But as exhaust pressure raises with RPM then the exhaust pushes more/leaks more into the cooling system and the motor begins to overheat from the lack of FULL water in the water jacket, and the lessened water flow caused by exhaust pressure within the cooling system.

Lift the powerhead off the midleg and replace the gaskets on BOTH sides of the adaptor plate. Do NOT use any sealer, clean the aluminum surfaces with acetone or another high quality solvent, install bare, dry gaskets, preferably OEM. If you insist on using any sealer, only as THIN as possible and let dry 30 minutes before installation. You do NOT want anything that cause this gasket to slip or blow out of position under pressure of WOT. NO silicone here.

I have been known to take a small punch and make little 'dots' raising the surface to provide a bit of 'traction', grip, bite, tooth, whatever you want to call it, to assist the alum to 'hold the gasket in position while under WOT loads, just along that line between the exhaust and water passages. Don't get carried away, tiny love taps on the center punch with the smallest ball-peen hammer is enough.

 

[j_martin]

Re: Mariner 175 overheating problems......

I think the poppet hole exhaust would be normal, because it dumps right into the mid, where other cooling water and exhaust goes. Before the pump fills things up, exhaust would come back into the poppet via the triangular shaped hole that normally carries water from the poppet to the mid.

Sounds like yer motor is worn out, though. If ya go through it at this time and freshen it up, you'll probably fix the cooling problem in the way by with new gaskets.

hope it helps
John

 

[dclange]

Re: Mariner 175 overheating problems......

CharlieB,
First thanks for all your replies and help. I've done some more reseach and found something interesting on the motor. This is looking at the motor from the rear. At the bottom of the block, in the back, their are four studs that come out of the bottom of the block, through I guess is what your calling the exhaust manifold, are exhaust adaptor plate? Is it about 1 1/2" thick and is bolted to the bottom of the block? Well, one of the nuts and lock washer on one of the studs is loose. So loose, I can see the threads of the stud between the bottom of the block and the lock washer. It's the rear stud under the port side head. The other three studs on the rear of the block are tight. Where the one nut is loose, their is a oil film all over everything, oil pooling on top of the manifold/adaptor plate, in that area. When you look at the area under the starboard head studs, that same area is dry as a bone. Where the nut is loose, right on top, where the block meets the manifold or plate, it looks right it has been blowing out carbon/exhaust. I think this is where one of the gaskets, the top gasket is that your talking about replacing. Would this be where exhaust could be exiting, or air being sucked in to the water jacket? I doubt this, but do you thing tightening up the bolt would make a difference in the problem? Are is this proof of what you are saying about the gaskets? I looked up the gaskets. (I think I have the right ones, about $11.00 each) When you say lift the powerhead, do you mean the whole motor, block , heads, etc.? This don't look are sound like a easy job, even though the gaskets are cheap enough! Could I do this in my basement with a comealong hooked to the beam?
I also have a thread going on this at www.bbc.com, under the Mercury forum, if you would like to check it out. Just trying to get all the opinions possible on this. As you'll see, a couple of them guy's are thinking the same thing you are. I'll wait to hear back from you......Thanks again.......Dave

 

[CharlieB]

Re: Mariner 175 overheating problems......

Exactly the gaskets that I mentioned.

If that side of the exhaust passage gasket failed and is leaking outside, I'd bet money it is also leaking INTO the cooling water passage which is on the other side of that exhaust passage.

Check your PM's

 

[dclange]

Re: Mariner 175 overheating problems......

Post moved up!