Outboard overheating, but not all the time.

[Dignity]

Dave, hope you resolve your problem, mine was simply the thermostats. Don't know about not replacing them though. No special tools to take the leg off or putting it back on, just don't overtighten the bolt on the anode tab as you will strip the thread. Mines a 150 hp and I managed it without any worries.

sam

[newchum]

hi dave, if i were you i would start putting my pots in deeper water and save the heartache. hope the little blighters were tasty

[T-REX]

Just a quick thought: while your checking around have a look at the temperature sensors on each head. These things don't last forever and it could be the source of the problem. Some of the guys on this site can probably tell you how to test them or just get new ones. Replaced one on an omc and I think it cost around $60.

[davez104]

OK, the water pump impeller has been replaced, I will take it for a run tomorrow and see if it has made any difference. The old impeller seemed to be OK, the rubber was a bit harder than the new one, but still pliable. There was not a lot of wear and there was no chunks out of the rubber at all. Hopefully it will be enough to make the difference, if not, the search will continue.

Thanks.
Dave.

[davez104]

Just back from an hour or so at the dam playing around. Couldn't get the motor hot no matter how hard I tried, so I guess it was just the pump after all.

Thanks for all the advice.
Dave.

[Dignity]

got to have some luck some time, glad it was nothing serious

[davez104]

Yeah, ya win some, ya lose some. As I was coming back in the driveway from the dam, I jumped one wheel up the gutter and broke a spring on the trailer!! They mustn't have been too good to start with, although they didn't look too bad. Oh well, I guess that will give me something to do this weekend, new springs Better there than halfway to Rocky I guess.

Dave.

[davez104]

Dredging up an old thread here. It's been a long time since I started this, but I took the boat out not long after the last post and had the same overheating drama, so cracked the sh!ts and put the boat away. Been busy with new job, move house etc so had not used the boat in a long time. Took it out today and the problem is probably worse than before. So cracked the sh!ts again and I'm pulling bits off and going to try to find where the blockage is as I think it has to be a blockage of some sort.

What I'm chasing is the schematics for this engine, 1990 Mercury 135HP Black Max. There was a link posted on the last page but it no longer works. Just wondering if anyone can help out.

Thankyou,
Dave.

[Pazz01]

Dave,

I had a similar problem with my 200 mercury offshore (97 model). When it was rought and had to cruise just on the plane around 1800 to 2500 rpm the damn thing would get hot.

I took it to the mechanic and he said it was all fine etc, then it would happen again.

I managed to get into contact with a mechanic in Ingham (Leo's Marine I think) that had the same motor and the same issues. He said he heated up an "element" (I'm not really mechanically minded to explain it) that contained two springs. When hot enough he said the springs would drop out and it will be find. It sounded very similar to the one that fishingjew said on the 30 March 2007, but you remove the spring.

The mechanic I had did not want to do this because of warranty etc, but I was sick of it and just told him to do it. He did it and I have never had to go and see him again. That was probably 8 years ago. Motor has nearly 400 hours on it now and still goes like a gem.

I'd suggest seeing a merc mechanic and explain the issue, but I'd say see an older one that has worked on them for many years. They should have seen this before, because I know of at least 2 mercs that have the same problem.

All the best.

Pazz

[davez104]

Thanks for that Pazz.

I've just finished putting everything back together. All the water jackets are surprisingly clean, at least a lot cleaner than I expected for a motor pushing 20 years old. I can find nothing that could be even partly blocked, water flows freely everywhere I looked. I really need to get hold of the schematics again so I can see where else I can access the water jackets.

I still have not checked to see if the guage is reading correctly, but I suspect that it is, the water from the tell tale is pretty hot when the guage reads hot.

Next step is to find a good mechanic, if such a beast exists around here, and get them to check it out.

Thanks,
Dave.

[peterbo3]

Dave,
If you are heading down to the coast, the OB mech at Sarina is very good. I used him & he was both reasonable with the $$$ & very competent.

[BM]

Dave,

You have replaced the waterpump impeller and presumably the top housing and lower wear plate were in good order.

The thermos have been tested and are operating as expected.

Have you pulled apart the poppet valve assembly and cleaned? Starboard side, just above the point where the powerhead joins the exhaust plate.

Also, for the V6 Mercs its very important that when you have the lower unit off there is a vertical divider between the waterpump assembly and the exhaust housing. When reassembling you need to add some silicon to the top (and sides if needed) of this divider. This is a common problem for the older V6 Mercs and if you don't seal that area properly then exhaust gas gets into the waterpump area and aerates it, giving you inadequate cooling.

I would also use an IR temp gun and check what the actual cylinder temps are when she's showing too hot.

By the way, has your overheat alarm ever gone off and do you know if it is working? Do you get the beeping test tone from your control box when you switch the key on?

Cheers

[davez104]

Thanks heaps, that gives me a few more things to look at.

I do get the test tones when I turn the key on and yesterday was the first time I have let the temp get high enough for the alarm to go off, so yes, it has gone off.

I have not done the poppet valve, thats what I was chasing the schematics for, I'll check it out today. I'll also seal around the leg, I wasn't aware of that, but it makes sense.

Thanks again,

Dave.

[dreemon]

BM, made a good comment about silicon on the divider between the w/p and exaust, my mobile mech told me he does that to all o/b when he pulls the leg off, and grease the threads on the leg bolts

[davez104]

Pulled the poppet valve out, clean as whistle, so no dramas there. Pulled the lower leg off and siliconed the join up. Any other ideas before I go for my next test run?

Thanks,
Dave.