1987 Mariner 175

[jakejake]

I have a 87' Mariner 175 that has started to overheat. I recently replaced the lower unit and water pump. Here is what I have done and seen so far. It appears the water pressure in the engine is really, really high. It pegged out and ruined my in-dash pressure gauge which I have not been able to replace yet.(about 30 to 35 psi) The pee indicator is almost non-existent. I have replaced both thermostats and rebuilt the poppet valve and gone back in and completely replaced the water pump components all the way down to the lower housing. Judging from all the different information I am able to find online i'm thinking I might have somehow gotten a blockage in the internal part of the engine. I remove the water line from the top of the block that feeds the water pressure gauge when the motor is running on the hose and it sprays a stream about 10' high and yet the pee indicator is either not spraying at all or only spraying a very weak 1' to 2'. Any ideas on how I can determine if there is a blockage and how to correct it if it turns out to be blocked?

 

[racerone]

Re: 1987 Mariner 175

You might want to do a " no cost " compression test.--------Blown head gaskets can be an overheat problem.

 

[jakejake]

Re: 1987 Mariner 175

You might want to do a " no cost " compression test.--------Blown head gaskets can be an overheat problem.

I did this already. All 6 cylinders tested at right at 90lbs. I know this might be low but thought that since all 6 were the same it probably wasn't a blown head gasket. Is this right?

 

[racerone]

Re: 1987 Mariner 175

Sorry , I only mentioned that because it was not indicated in work done in your first post !

 

[jakejake]

Re: 1987 Mariner 175

Sorry , I only mentioned that because it was not indicated in work done in your first post !

No problem! I probably have failed to mention several things. I have been dealing with this for a week now. I hesitate putting this motor in any of the local shops because my experience with them is that I might get the boat back in 6 weeks if I'm lucky. Can you tell me if removal of the heads gains me access to the interior water jacket or water circulation areas so I could check them for a blockage? The fact that this problem seemed to just happen all at one time also tells me that maybe I did have something stop up. Strong water flow in one area and weak flow in another is confusing to me.

 

[carholme]

Re: 1987 Mariner 175

Have you checked the pee tube for blockage? Mud daubers are notorious for getting up in there and creating their nest which will completely block the flow. As well, you may have a blocked or inoperative water pressure relief valve, preventing flow through the pee tube.

Do you have the s/n of your engine?

Gerry

 

[out 2 launch]

Re: 1987 Mariner 175

A bad head gasket may cause this problem. I have seen gaskets that will leak compression into the cooling system but not allow water into the combustion chamber. One would think that a compression test would show leakage but remember that "compression" pressure and "combustion" pressure are vastly different.

 

[Chris1956]

Re: 1987 Mariner 175

That motor would normally never have water pressure over 10PSI or so. Not sure what your issue is, but it is not with the waterpump or poppit.

 

[Dukedog]

Re: 1987 Mariner 175

At less than 90 lbs its time ta take it apart anyway. If your gauge is accurate. That's a chrome bore motor and any neglect can cause some serious damage. That motor should be at tha very least 115 lbs.
Usually two things cause tha higher pressure. Like ya say, blockage, poppet. Air will show high also but usually fluctuates. At times tha blockage will be in tha adapter plate. Can be blown out adapter plate gaskets. Has tha discharge at tha prop changed?

2 stroke makes compression on every stroke............

 

[jakejake]

Re: 1987 Mariner 175

Have you checked the pee tube for blockage? Mud daubers are notorious for getting up in there and creating their nest which will completely block the flow. As well, you may have a blocked or inoperative water pressure relief valve, preventing flow through the pee tube.

Do you have the s/n of your engine?

Gerry

I replaced all the water hoses from the outlet on the side of the block up to both thermostats and down to the pee port. I'm not sure if it matters but when this happened I took the thermostat housings off and there were no thermostats on the motor. I purchased two new ones and installed them. I bought the boat/motor 5 years ago and have fished it pretty heavy over that time with only a couple of times having to replace impeller.
I do have the S/N and will post it when I get home.

 

[jakejake]

Re: 1987 Mariner 175

At less than 90 lbs its time ta take it apart anyway. If your gauge is accurate. That's a chrome bore motor and any neglect can cause some serious damage. That motor should be at tha very least 115 lbs.
Usually two things cause tha higher pressure. Like ya say, blockage, poppet. Air will show high also but usually fluctuates. At times tha blockage will be in tha adapter plate. Can be blown out adapter plate gaskets. Has tha discharge at tha prop changed?

2 stroke makes compression on every stroke............

I rebuilt the poppet valve with new spring and diaphram. There is a bleed hole in the outer cover of the poppet valve that now bleeds water at all times. Is this normal? (I assume this is a pressure relief hole)

 

[racerone]

Re: 1987 Mariner 175

That is a vent hole that allows the diaphragm to move.----If water leaks out then you may need to inspect gaskets / sealing surfaces.

 

[jakejake]

Re: 1987 Mariner 175

The S/N for this motor according to the title is OB184204. When I got home from work I removed both thermostats, put it on the hose and started the motor. It had a pee stream immediately but it wasn't like it use to be and it gradually reduced down to about 12".

 

[jakejake]

Re: 1987 Mariner 175

Another interesting point. I was told by the Mercury supply store in Plano Texas that my motor model number was 7175726. But when I search this model number it comes up as a 1986 262HP. I also don't find any parts lists that show that Mariner even made a 175hp in 1987 like the title states. I don't find a 175 until 1988. Not important or have I been living a lie???

 

[wired247]

Re: 1987 Mariner 175

You actually have a 1986 175 HP 2.4 liter . The serial number is 0B184204 and the model number is 7175726. 175 HP Mercs go back to the 70's. Things get confusing when you are dealing with states that have outboard motor titles separate from the boat title. Sometimes the sale year is listed as the model year. Outboards can stay on the shelves for years.

I would try a different compression gauge and possibly a different water pressure gauge.



https://webapps.brunswick.com/literature/literatureSearch.do

 

[jakejake]

Re: 1987 Mariner 175

You actually have a 1986 175 HP 2.4 liter . The serial number is 0B184204 and the model number is 7175726. 175 HP Mercs go back to the 70's. Things get confusing when you are dealing with states that have outboard motor titles separate from the boat title. Sometimes the sale year is listed as the model year. Outboards can stay on the shelves for years.

I would try a different compression gauge and possibly a different water pressure gauge.



https://webapps.brunswick.com/literature/literatureSearch.do

I will purchase a new water pressure gauge tomorrow and install after work. Here is how I tested the compression! I pulled my kill switch on the controller. I would then remove 1 spark plug, attach compression gauge and turn the motor over two or three times. Each cylinder would pressure up the gauge to just about 90lbs. Did I do something wrong? Also another tidbit of information that probably isn't important. When the mechanic at the Mercury shop found out I didn't have any thermostats he told me I probably had a lot of carbon build up in the cylinders and he told me to remove plugs and spray a good amount of Mercury Power Tune in each cylinder and let it sit for several hours. Then blow it out and reinstall plugs, attach hose and start engine. He said I should see a lot of carbon flush out the exhaust but when I cranked the engine I only saw clean water. No carbon.

 

[jakejake]

Re: 1987 Mariner 175

After my last post I realized that I had not tested compression since I actually sprayed the cylinders with the Power Tune. So I went out and removed all plugs and tested each cylinder. All but 1 tested right at 100lbs. The middle cylinder on the right had side tested at 96lbs. I sprayed down the cylinders again and will let them soak all night....

 

[wired247]

Re: 1987 Mariner 175

Run it to warm it up, pull ALL the plugs, open the throttle up and jump the starter relay to crank it over until it doesnt build any more pressure . Throttles need to be open so you cant use the key switch unless you disconnect the throttle linkage and open them by hand. That will give you the actual compression.

If you didnt have any thermostats and it ran for a years like that I wouldnt be surprised if your bores were worn out.

 

[Dukedog]

Re: 1987 Mariner 175

I rebuilt the poppet valve with new spring and diaphram. There is a bleed hole in the outer cover of the poppet valve that now bleeds water at all times. Is this normal? (I assume this is a pressure relief hole)

Are you talkin' about a small "weep" hole or a regular hose bib? If its tha small weep hole (maybe 1/8") tha poppet is screwed up! Comp. checked right and 100 or less its still time ta do something with it............

 

[jakejake]

Re: 1987 Mariner 175

Are you talkin' about a small "weep" hole or a regular hose bib? If its tha small weep hole (maybe 1/8") tha poppet is screwed up! Comp. checked right and 100 or less its still time ta do something with it............

I'm referring to the small weep hole in the cover of the poppet valve. It just spits/weeps water the whole time the motor is running. I have already replaced the internals of the poppet valve. (spring, diaphram and gaskets). BTW: it didn't do this prior to me taking it apart. Or at least I never noticed it and I'm pretty sure I would have.