Overheating Outboard

[Audiofn]

Hey all I have a outboard problem and I hope to get some help from you all. I have a few outboards that are all doing the same thing. They will run cool at idle but when you go to plane off they heat up very fast (can not even get on plane with a hydrostream). What the hell is up!!!! I have checked the heads, head gaskets, checked all holes for blockage, put T-stats in taken them out, replaced popet valve, water pump, waterpump base gasket, blew out all the holes for the water passages and everything else I could think of. Oh ya this is happening on a early 80's 225 and also a late 80's 200 with oil injection. If you take to popet valve out of the 200 then it will at least allow you to plane off but not go WOT. You guys have any ideas?

Jon

[WillyT]

When you say you checked all the holes for blockage, are you including the holes that are under the exhaust cover plate in the rear of the engine between the cylinders? These can become clogged with "crud" and and need to be opened with a small drill bit turned by hand (will need new gasket for cover). My engine got so hot from this that the paint came off of the block. Is your water pressure good or bad? Pressure will still read good if these holes are blocked. Is water coming out of the "pee hole" as you would expect?

[Audiofn]

Yup checked all that and no problem from what I can remember. It has been a real odd one to track down.

Jon

[Checkmate Mike]

I'd be interested in knowing what your ultimate solution is. I've got an '87 200hp that runs hot as well. I've replaced the water pump and that helped a little. I'm now considering a nose cone or a different lower unit with lower water pickups to improve water pressure. If I keep the water pressure above 12psi I'm usually OK. But I need to lift the motor higher to get speed which usually results in the water pressure dipping below 10psi. That's when temperature climbs.

Regarding the electrical issue posted on shorting. I've got a temerature switch (beeper) and sender (gauge) in my motor. One on either side of the heads. Both seem pretty consistent so I suspect I've got a temperature problem, not electrical.

Where is the popet valve you speak of? What was the impact on the water temperature?

Would appreciate any insight based on your experience.

[Audiofn]

I have checked the temp and let me tell ya it is so hot you can barely put your hand on the motor. All my other motors run cool. It is not even uncomfortable to put your hand on the heads. These things feel like they will burn you. So there is definatly a problem in there some were. I have checked with Merc techs and all over with guys like you. I was thinking about writing to the guys in the mags and see if they have any ideas. This is killing me to have this many bad motors!!

Thanks for all the help and if something comes to mind please let me know. I am not above trying anything at this point

Jon

[seacow]

have had 2 do similar problem, don't know exactly your situation but both of these were powerhead gaskets, took us about 2 days both times to narrow it down to that but we didnt have anywhere else to turn, dont know if you have thought of this but it may help, gasket only cost a few bucks and dont take long to replace

[Audiofn]

Ya we tried a couple of those also. Thanks

Jon

[Markus]

Aufiofn, is your water pressure OK, or is it too low?

[Audiofn]

Water preasure now with no popet is a little low but that is what has been giving us the best results. Water preasure with the popet is certainly in line with the other motors that we run.

Jon

[Audiofn]

I figure some how air or even exhaust is getting into the system. I jsut can not figure out were. There is a lot of air in the water out the tatle tale stream. Again I did check the heads and block for straitness.

Jon

[DaveR]

Referencing 2.4's....I'm no expert, but it is my understanding the poppet valve ( located undere the cover just below the electronics and above the cowel pan on the starboard side of the block) is there to keep water in the block at idle / low RPM. It's spring loaded. I don't believe it will have any effect on temperature at speed. If you have the heads off, look for sections of rubber hose in the water jacket inserted between the cylinder and block. Originally there were two, one on #5 and one in #6. they are there to direct water flow. Prof. O.B. - a VERY knowledgable poster we all miss - modifiys the system by adding two more - one in #3 and one in #4 I believe. He also opens up some water passenges. I have an e-mail and a drawing discussing these changes. Drop me a line if you think they'll help.

[Edited by DaveR on 05-17-2001 at 08:55 AM]

[Audiofn]

Dave I though about that but I do not want to band aid the problem. I thought of that solution as a band aid. Somewere there is something that we are missing.

Jon

[Rocket]

If you live in the south, I have seen mud dobbers( type of wasp) build nest's just in side the motor & water jets where you can't see them. BLOCKAGE!

[Audiofn]

I live in the NE

[sosmerc]

You may have a bad exhaust divider plate...corroded or cracked. Be sure to replace all the exhaust gaskets as well as the plate.
We need to know exactly what your water pressure readings are at various rpm's. Also, have you done a cylinder leakdown test? A leakdown test may reveal head gasket problems...a simple compression test may not be as revealing.
Is the engine using the original exhaust adapter plate? What if any mods have been performed?
Stock gearcase?
What transom height?
Really need to know your water pressure.

[Jerry Millington]

HI i also have the same problem 1985 200hp.
I did almost everything so far the last thing
i did was remove the exh. section (divider)looked
in great condition and replaced the gaskets.
I also removed my poppet valve (round style no hose
connection)ran cooler running it on the hose but
did'nt run it on the lake yet.
Water presure with valve in 10 to 18psi at any rpm
presure without the valve with the garden hose on it
about 5 to 8psi and goosed it and no presure change.
richie

[Audiofn]

Richi from what I have heard your hose can not produce enough water to run the motor at high RPM's. I have replaced the exhaust divider gasket, but not the plate. We took off the head gaskets to both see if we had a bad head gasket and also to see if there was a blockage. Unfortunatly I can not remember the water preasure numbers as it has been a while since we worked on the boat. I remember it being in the neighborhood of what the other motors are that we are running with no problems.

Jon

[tommyT]

I know this sounds dumb but check and make sure your water pump gaskets are all in the correct position and orientation. I had this problem once on my 2.5 mariner and it took me several attempts to figure it out.

[Audiofn]

Tommy thanks. I have checked that a couple of times. We had that happen to the water pump on the race boat and blew a motor. About a 1/8th of an inch poped out of the bottom gasket and it was enough. We have dropped these motors on different boats and still had the problem, and then put other motors on the mid sections and all was fine. It is a very confusing situation. I am glad that I am not the only one, now how to figure it out!!

Jon

[Dave Estes]

Check your primary pickup timing. I had a 2.4 that was running so hot on the hose the water out the peehole would literally burn you. Checked primary timing and adjusted, cooled off immediatly. My 2.4 has had the water rerouted and xtra holes drilled in the back. Runs 22psi at 6400 with a 27' Yamaha, 1/2" above pad. Bob's with extra holes in top of cone.

[martyc@tinet.ie]

I have done everything you have already mentioned to no avail.Changed Head gaskets cleaned jackets,taken out exhaust plate new gaskets,new stat new water pump impeller,and its still getting too hot(i even installed a tell tale as there is none on this older engine)..How do i check the water pressure...and what pressure should it be reading.When i take the water hoses off the cylinders there is water circulating but i dont think it looks like its under any great pressure..
Marty.

[stan merck]

I KNOW YOU SAID YOU HAD THE HEADS OFF AND CHECKED ALL COOLING PASSAGES BUT WHAT I HAVE SEEN HAPPEN IS THAT EVERYTHING IS CLEAR BUT THERE IS JUST ENOUGH BUILDUP OF CORR CALCIUM OR SOME LAYER OF CRUD RIGHT AROUND THE CYL JUGS THEMSELVES THAT THE WATER CAN NOT PULL THE HEAT AWAY FROM THE CYLS. YOU CAN EITHER SCRAPE AROUND EACH CYL AND REMOVE IT. OR THIS SOUNDS STUPID BUT IT WORKS. GET 6 OR 7 BOTTLES OF LIME AWAY AND PUT IT IN A SMALL BARREL JUST ENOUGH TO COVER INTAKES ADD WATER AND RUN IT THROUGH THE ENG. IT CLEANS THEM OUT SPOTLESS AND DOES NOT HARM RUBBER. OR DROP THE LOWER UNIT AND HOOK UP A BILGE PUMP AND CIRCULATE IT THRU THE ENG FOR 45 MINS OR SO. IF RUNNING ENG IN BARREL IT WILL OVERHEAT SO BE CAREFUL. THIS WORKS HAVE SEEN MANY YAMAHAS WITH THIS PROBLEM AND IT CAN HAPPEN TO MERCS TOO. USUALLY ENGS THAT SEE SALT OR BRACKISH WATER.

[martyc@tinet.ie]

Sounds like a good possibility,i was wondering myself what would be a good product to rem,ove the crud...
Cheers,
Marty.

[Audiofn]

The insides looked good as new on this motor. We also checked the timing and it was ok. Keep them comeing man I know some one will think of it.

[CharlieB53]

What is the common factor on these engines?

Have they all been on the same boat?

Is there a restriction in the fuel line, fittings, tight bend in a fuel line?
Too tight zip tie strap holding electrical wiring to the fuel line leading to the engine, 'pinching' the fuel line, slightly restricting flow at WOT?

Low octane fuel?

Even a combination of all the above.