Runs HOT at 3800+ RPM's

[davidzima]

Motor runs all day at 3200-3400 RPM's, Will run about 5-10 Min at @4000 and temp will creep up then rev limiter kicks in...HOT. I wasn't paying attention and that was the only time It got that hot. Changed water pump/thermostats and same thing. The water pump that I replaced looks great, in tact, and still very plyable. Did not notice this when I bought it and tested it.
Pee stream is more of a thick spray than a good stream.
Water pressure stays below 10psi if Guage is accurate.

If there is a blockage (say part of an old impeller).. is there any advice on how to approach it?

Thanks in advance.
David

 

[Laddies]

Re: Runs HOT at 3800+ RPM's

It could be a stuck popit valve but it's hard to say I can't see the engine and you forgot to give us the model

 

[davidzima]

Re: Runs HOT at 3800+ RPM's

Sorry...1994 Mariner 225 3.0L Carb

 

[Laddies]

Re: Runs HOT at 3800+ RPM's

I would replace the popit valve diaphram, check the valve for wear and probable change the spring

 

[davidzima]

Re: Runs HOT at 3800+ RPM's

Thanks Laddies,
I will do that, but that wouldn't restrict the pee stream or cause the water pressure to be so low would it? If I do look for some kind of blockage of water flow what would be the best way to go about it?

 

[freddyray21]

Re: Runs HOT at 3800+ RPM's

not sure on the merc outboards, but on the mercruiser probably the same if the water pump housing it out of shape at all they will suck air at higher rpms and starve for water.

 

[Laddies]

Re: Runs HOT at 3800+ RPM's

Fred brings up a good point did you seal the area between the exhaust and pump cavity with RTV sealer? As far as the telltale flow that is usally restricted by the thermostats intill they open. If the water presurre drops as the RPM increases then you may have a air leak at the pump or a blockage in the cooling system

 

[davidzima]

Re: Runs HOT at 3800+ RPM's

The pump housing is sealed. The water pressure goes up as RPM's increase but not like I think it should. It will be just below 5PSI at idle and move up to 8 or 9PSI. I was thinking it should be more like 15PSI.
I will still take care of the POPIT valve as you suggested laddies.

 

[Laddies]

Re: Runs HOT at 3800+ RPM's

David, if you want to increase the water pressure you need to change the spring on the popit valve that is what hold the popit shut and a weak sping can open at a lower pressure

 

[gss036]

Re: Runs HOT at 3800+ RPM's

I agree w/Laddies but, if it were mine, I would change all the parts in the poppet, not an expensive item. Water pressure should be at 10-12 psi at wot.

One thing I do occasionaly is run water (40-60 psi) back through the pee hole hose. A little back flo never hurts and may very well help.

 

[fishinjack]

Re: Runs HOT at 3800+ RPM's

I had the same problem in my i/o merc, It was the impeller . I had cahnged checked adjusted many things and after all of that it was the impeller, cheap fix too, try it first.

 

[davidzima]

Re: Runs HOT at 3800+ RPM's

Thanks for all the advice,
All poppit parts are on order, Impeller(and all water pump parts replaced). I will try to figure out a way to hook hose up to Peehole tube to run water backwards thru system.

David

 

[gss036]

Re: Runs HOT at 3800+ RPM's

To run water backwards in the pee-hole tube, just disconnect inside the cowling and and use a hose spray head and push it tightly on/into the 1/4 inch hose. Pretty simple.

 

[davidzima]

Re: Runs HOT at 3800+ RPM's

OK...I replaced all components to the Poppit Valve. I did find that the rubber grommet was not seated correctly on the carrier so that water could pass by the poppit without it actually having to open.
Now I have a good strong pee stream but the motor is overheating very quickly. Even at idle it is about 160 Deg. I took it up on a plane and Temp. rose to around 190 to 200 quickly and I went back to Idle. It slowly came back to the 150-160 range. Before I could run all day as long as the RPM's were at 3400 or less.

New complete water pump.
New poppet assbly.
New Thermostats
Good Strong Pee Stream.

 

[CharlieB]

Re: Runs HOT at 3800+ RPM's

On occasion an adaptor plate gasket fails and at higher speeds exhaust enters the cooling system, blocking flow and raising temps.

lift the powerhead and replace that gasket, also check for any foreign matter in those passages while you are there.

 

[SPUNWHEELS]

Re: Runs HOT at 3800+ RPM's

When a water pump change, doesn't do it, and the thermostat, poppet checks don't do it, and a motor has seen any salt water at all, super strange corrosion sets up in the whole engine system, thermostat housings, cooling jackets etc. and causes a lot of engine failures. Sometimes the copper pipe feeding from the water pump itself will get a hole in it. Sometimes you can see it when you drop the lower unit, and effect a cost effective repair, and sometimes you have to tear into the whole thing, just short of the piston crankshaft assembly.

Running a garden hose flush often times isn't enought to keep the corrosion at bay. Pulling the power head off and cleaning out every passage doesn't appeal much to any one. Pulling the heads will give you a quicker indication of how much white stuff you got inside the engine, as well as any pieces of authorized material stuck in places they shouldn't be.

I often wondered if running an engine like this in a closed system like a barrel of water with a chemical solution additive, could in fact expose or repair the major cause in these cases, plugging the pisser with a sheet metal screw to circulate the complete cooling system in the closed circuit till it reached full operating and cooling down temps repeating this several times. I know this is a time consuming process, but the alternative of removing broken bolts and repairing stripped thread holes, is something I have done too much of in my life already. Often times just observation in a test tank like this will guide us to the next step. Just my thoughts.

 

[davidzima]

Re: Runs HOT at 3800+ RPM's

SPUNWHEELS...That seems like something that would be worth trying. What kind of solution could I run thru that would not effect/hurt the tubing / gaskets etc but still disolve corrosion? Maybe something like CLR or something stronger?

 

[j_martin]

Re: Runs HOT at 3800+ RPM's

Sometimes you run over a rotton deadhead and wind up with a lot of the little holes in the cooling system plugged up with wood chips. I've had this happen with some kinds of seaweed, also.

Look at it this way, when the poppit was jammed open, it almost cooled. With it holding back the pressure like it should, (forcing water out many other small dedicated passages) it overheats quickly.

I think you need to pull the heads and exhaust plate, take a look, and probably then decide to lift the powerhead and get it all cleaned out. I think you'll find all kinds of chit plugging up small water passages.

If the motor is basically good, it's worth the effort. If you mess around long enough, you'll hurt it and the overheat problem will be a mute point.

hope it helps
John

 

[jozwhales]

Re: Runs HOT at 3800+ RPM's

I have same problem with my 1996 200hp Mariner. But I did a total rebuild on the sucker, rebore, new pistons, gaskets, the works, but couldn't really find anything that would make it overheat. Has good pee, idles at around 160, go up on plane and immediately jumps to 200. I've replaced everything. I've been a mechanic all my life and this sucker has got me stumped. I hate mercury. Knew I shouldn't have bought this boat, but it was cheap. Well, not any more. Thought once I rebuild and replaced all the gaskets, poppet, etc. it would cure the problem, but it hasn't. Previous owner said it always ran hot, but it shouldn't run this hot. Think he just wanted to dump the boat. My thinking is maybe i need a different spring in the poppet. Any suggestions would greatly be appreciated before I commit suicide.

 

[gss036]

Re: Runs HOT at 3800+ RPM's

I have read posts where people have cut a length out of the poppet spring. Do you have a water pressure guage?
I have also read post where the seal/slinger on the water pump and at the exhaust plate were not seated correctly. One you do the obvious, it becomes a real challenge.