'88 Mariner 175 HP Overheating...help!

[apaseman]

Hello,

It has been a good 6 months since I have had my boat out, and yesterday when i pulled out my boat and connected the hose to make sure it would start I noticed that it would start to pee really fast (which is not normal). I touched the water and it seemed noticeably hotter than usual, but steady.

So today, I took it out, idled out and when I got to the area where I could open it up, about 2 seconds into my trip my overheat alarm sounded. I turned off the motor, restarted, and tried again, and the overheat alarm screamed again. So, i idled back to the dock and by the time i got back the alarm screamed at idle too.

I need help...I can't afford to take it to a shop right now. What can I do to go about attempting to find the problem? At least at the surface the water pump seems to be working, I get water coming out of the motor..but its' very hot.

Thanks for your help

Adam

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

I forgot to add that if your facing the prop of the motor, the right side of the engine seemed noticeably hotter than the left.

 

[j_martin]

Re: '88 Mariner 175 HP Overheating...help!

Poppet's stuck, or plugged.

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

Any idea how I'd go about figuring out how to unclog or unstick that?

 

[ufm82]

Re: '88 Mariner 175 HP Overheating...help!

Poppet valve is on the starboard side of the engine down at the bottom. You'll need to split the lower cowling to access it. It's under a figure 8 kind of looking piece. It's easy to change out and not expensive. However the poppet doesn't open until you get over 1,500 RPm or water pressure opens the valve when when you are running.

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

Ya I think i'm having other issues that are causing my overheating. I found the poppet valve, thanks, replaced some gaskets but other than that it seems fine, there wasn't anything blocking it.

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

Well, I have done what I can to figure this out, and I can not get the overheat alarm to sound running my motor with hose atached even after rev'ing the motor. Unfortunatly It's gonna cost me another launch fee just to see if my tinkering has done anything, which I can't imagine it has because all I did was take out the poppet vavlve, replace two gaskets, put it back in, removed the Tstats, replaced the gaskets on them.

 

[yamatech43]

Re: '88 Mariner 175 HP Overheating...help!

Why not test the t'stats? And crank up the engine with a t'stat pulled, should have water gushing out of head....i would worry about the one on head that is getting hotter....if you can tell difference with your hand then that is your problem area....you in salt water, that would be nice to know....if so you may want to put some neutra salt(at Volvo marine dealer for a few dollars) down thru engine and let sit a while(10 mins) then do it again....will remove salt,scale, residue, amazing stuff. You may end up having to remove exhaust cover on that head to clean out crap....but try the neutra salt and test t'stat first. You know, get a thermometer and heat some water on stove....observe what temp tstat opens

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

This really is a great forum, I've always had so much help from the members!

I ran the motor with no T-Stats in, water came up both engine blocks, but the port side (is lower) water came out great but the starboard water came out, but not as good. I concluded that this was because the port side block was lower, so I put the T-Stat in the port side and water then came out the starboard side great (I assume indicating that there was not a blockage).

Last night, while I couldn't sleep, I think I may have realized what the problem could have been. When I took out the Poppet Valve, I remember not having to unscrew the screw that holds the washer to the plastic valve too much, and If i'm correct in my thinking, if that screw was unscrewed (from vibrations i guess) it would actually push the valve closed and would not allow it to open fully, therefore limiting the amount of water that cools the engine at higher RPM's. I just remember having a brief moment in my head where I was surprised at how long the screw was and didn't remember having to unscrew that much while taking apart. So, I'm hoping that was indeed the problem, which I'll find out today when I launch the boat again.

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

Well, I took it out on the water, and once again the ovrerheat alarm screamed at me, though it took a bit more than last time. I'm at a loss. It does not overheat at idle and low RPM's but over 2000 (it seems) the overheat alarm sounds. I have:

Checked for a block or problem with the Poppet Valve, nothing i could see.
Ran the motor with the T-Stats out to see the flow, which seemed fine
Took the lower unit off to check the water pump and impeller..(considering I changed this less than a year ago with not too much use of the motor I didn't figure this was the problem) and the impeller seemed fine.

So, i am at a loss as to what to do. I'm considering bringing it into the shop but these day's I don't have a lot of money to dump into my boat so part of me is thinking I'll just have a useless boat in my garage unless I can fix this myself.

 

[j_martin]

Re: '88 Mariner 175 HP Overheating...help!

The poppet plugs up at the triangular shaped port downward to the mid. Did you check that out when you had the valve out?

There's small passages in the head and exhaust cover area. Critters, seaweed, and even rotten log splinters can clog them up. (I have experience with the log.)

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

The poppet plugs up at the triangular shaped port downward to the mid. Did you check that out when you had the valve out?

There's small passages in the head and exhaust cover area. Critters, seaweed, and even rotten log splinters can clog them up. (I have experience with the log.)

Unfortunatly, I am not good with terms, I'm not sure where the triangular shaped port is, and a bit confused donward to the mid, so I do not believe that I checked that. I pulled the poppet valve out, could not see much passed the hole that it went into, and the valve itself seemed fine.

As for the small passages in the head and exhaust cover area, how would one go about checking these?

I really wish I knew more about these things. I bought a manual but honestly, it's a bit like reading a foreign language. I'm getting better (with the people on this forums help), but still have a lot to learn. I'd like to eventually be the type of boat owner that is self sufficient but it will just take time.

 

[j_martin]

Re: '88 Mariner 175 HP Overheating...help!

A poppet valve lets pressure off against a spring. If you look into the hole after you pull the valve off, you will see a round rubber seat for said valve. Where does that water go that the valve lets through the seat?

On your side of the rubber seat is a hole in the aluminum going downward (toward your feet), triangular in shape, and the other end of that passage goes into the midsection and allows the water to escape, mix with the exhaust, and go out the prop or relief ports. (holes above the water line in the back of the mid)

A good start on becoming the boat owner you want to be (self sufficient) would be to get the factory service manual for your engine and study it.

Your engine is approximately 1/6 as complicated as an automotive engine.

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

I have purchased the Seloc Repair Manual. I am studying it. Can't find where the poppet valve is in the manual so far lol.

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

I took the poppet valve out once again. I see the little triangle shaped hole. At the angle that it is in, I can not see if anything is clogged. Is there a specific way to tell? Should I run a coat hanger down it? It looks as though I could take off the piece between the lower unit and Power Head, but not ever having done this (and again, looking throgh the Seloc book i bought can't find any info on this) I do not want to just do it as It may create problems.

If i am correct in my thinking, water flows out this Poppet Valve from inside the engine? And then flows out through the bottom and exhaust area? The water flows from the pump up to the T-Stats fine, so the problem doesn't seem to be in that area.

Since the overheat revolves around high RPM's and not low, I can only assume that I do have a clog, or something wrong with my water pump, having low water pressure or something. I do not have a water pressure gauge. I feel like I keep asking the same questions, but I also feel like I have exhausted all the suggestions.

 

[j_martin]

Re: '88 Mariner 175 HP Overheating...help!

I have purchased the Seloc Repair Manual. I am studying it. Can't find where the poppet valve is in the manual so far lol.

I said,
Get a factory service manual for your engine and study it.

The Seloc manual is good for bung fodder. (outhouse supply)

 

[j_martin]

Re: '88 Mariner 175 HP Overheating...help!

I took the poppet valve out once again. I see the little triangle shaped hole. At the angle that it is in, I can not see if anything is clogged. Is there a specific way to tell? Should I run a coat hanger down it? It looks as though I could take off the piece between the lower unit and Power Head, but not ever having done this (and again, looking throgh the Seloc book i bought can't find any info on this) I do not want to just do it as It may create problems.

If i am correct in my thinking, water flows out this Poppet Valve from inside the engine? And then flows out through the bottom and exhaust area? The water flows from the pump up to the T-Stats fine, so the problem doesn't seem to be in that area.

Since the overheat revolves around high RPM's and not low, I can only assume that I do have a clog, or something wrong with my water pump, having low water pressure or something. I do not have a water pressure gauge. I feel like I keep asking the same questions, but I also feel like I have exhausted all the suggestions.

If you have done any reading on this site at all, you would figure out that it's almost impossible to definitively troubleshoot the cooling system without a water pressure gauge. You would also find out that water pressure is a better indication of cooling system performance than a temperature gauge is, on this engine.

As you might be figuring out by now, without more information, it's impossible to proceed.

 

[apaseman]

Re: '88 Mariner 175 HP Overheating...help!

I have attempted to find posts concerning this, with not much success other than things that have been stated here already...i.e. check the impeller, check the T-Stats, Check the Poppet Valve. So, I did read. I do not have a pressure gauge, but sounds like it would be a good thing to install. That being said, I never expect a definitive answer. I'm at the end of my rope on this, and am throwing in the towel. Boat 1, me 0. Time to decide if I call it a total loss or dump more money into it with taking it to a shop. Motor is 22+ years old and I fear I'm just putting good money after bad. Thanks for your time with the suggestions.