150 black max overheats at high RPM

[bobrock123]

I am looking for some professional advice. I have an 1989 or so 150 mercury. It has been on the boat for two years and was steady at 140deg, at 5800 rpm... Now at 3000 I get 180deg. If I go beyond that it will hit 200deg at WOT. I have changed so far ..... Impeller, Poppet valve, Thermostats. I pulled the powerhead and cleaned out the adapter plate. There was sand in there. Reassembled with new gaskets.. Took it for a test ..... It is a bit better ... 3000 rpm 160deg At idle I have about 4psi and 18psi at WOT. compression is 130 on all cylinders .... I am at a loss as to where to look next my serial # A933666 Appreciate any help....Bob

 

[sam am I]

Well, sounds like you covered all the bases.........pressure's good, hmmm.

"Gradually has got hotter? And the gauge is reading right?

How much sand? Enough perhaps to have plugged some of the block's water jacket exits ports? Perhaps sand has filled into the jackets themselves? Maybe enough sand in places to not allow proper flow but not so much to be reflected in over pressure on the pressure gauge.

Guess where I'd head is,

1) Is the temp sender (starboard cylinder head typically)/gauge reading right? Have you had a over temp alarm from the over temp switch? (port cylinder head typically, alarms at "240? F ? 8? F")

Got an IR temp gun to confirm the gauge?

If truly over heating, are both heads reading bout the same "over" temps? Or just the one head where the gauge's sensors lives? (starboard cylinder head typically)

If the gauge is reading right and one and/or both sides are in fact over heating, and with all that you've done (assuming correctly), I'd suspect additional sand/calcium etc blockages......

Last ditch.........I'd then remove both stats and the poppet and run it (still should have some H2O pressure, esp at speed). If it still overheated, I'd be pulling the cylinder heads for a peak ...........

Perhaps someone else here knows how and had success with some sorts of a back flushing method for sand.......

 

[CharlieB]

Before you start taking anything apart you need to check a few things just to rule them out. First, I have a question. How old is your fuel? If you have a portable tank you can hook up fill it with fresh fuel of the correct 50:1 oil mixture and repeat running tests.

Do you have an ignition timing light and know how to check your WOT timing? Remove all spark plugs, tape them together leaving the spark plug wires on each, add a piece of wire to the metal part of the spark plug bundle and Ground that wire. You HAVE TO have a place for the spark energy to go while testing.

Improper timing can cause excessive heating while under increasing load. It must be correct Check it.

Connect the timing light pick-up to #1 plug wire. Should be the highest cyl. Turn the key On. Shift into F gear and WATCH OUT for the spinning prop. Or take the prop off so you cannot bash your leg. Use a remote starter button to energize the starter relay . Watch to see that the timing light shows the flywheel mark aligning with the timing marker. If not dead on, then you will need to adjust the linkage that move the timer assy until the marks are aligned.

It never hurts to check compression to be sure they are all near the same. Different gauges will give different readings. Don't be bothered by a number unless the one is grossly different from the rest.

Watch each spark plug for spark, one cyl missing will cause heating on the other cyls.


This is why I always push people to start at square one. As some of the simple things can cause heating.

 

[Dukedog]

just tha impeller?... not tha ride plate and housing?... sand will put some unseen wear on those two stainless pieces affecting tolerances.....

 

[jimmbo]

Have you changed the set up, like raising the engine on the transom?

 

[bobrock123]

OK.... You guys have given me some good stuff to work with... I will check the timing.... as for the amount of sand .... not a whole heck of alot... cleaning it out made it better ...I did notice that all the cylinders were 130 psi except one was 122 psi. I will put some more time into it and get some answers..soon

Thank you for the replies.... you guys rock...

 

[sam am I]

Bit curious on this.......drop a note if ya figure it out.

 

[Chris1956]

I am also curious. I have a friend with the same issue on about the same year (clam shell cowling) 150HPV6. Everything checked out in the thermostats, poppit and waterpump. She only overheats at high throttle. My guess was a cylinder head leak into the cooling passage, but we never got around to pulling the heads.

 

[bobrock123]

Chris and Sam...... You guys rock.... you gave me some real good stuff to work with.... OK.... a few more observations.. when I hit about 5000rpm the water pressure was almost 24 psi.... So I went to do a timing check and found one whole bank not firing...turned out to be a bad stator.. Runs so much smoother and starts real easy.... but still over heats the side that was firing sensor goes to my temp gauge. tested the sensor and it is accurate... checked timing and found 9 idle and 21 at WOT......which is good from what i have gathered...rechecked all compression and it is perfect at 130 psi every cylinder. I cannot shake the feeling that this is a leaving water problem.....water pressure is good... And for Forks sake... I just realized I have 16 volts indicated on the guage at 3000 rpm... and that was on a fully charged battery..... If anyone has a break catcher laying around please send a PM.... Because I can't catch a forking break ! Bob

 

[bobrock123]

I am thinking of blocking off the poppet valve completely and send all the water through the block....

 

[sam am I]

Wait.....If you have a poppet valve like mine (has a control/assist hose tapped off the top of block running down to the poppet), in order to allow max flow,(as if you were WOT but now at any speed) you'll have to remove the valve from inside the poppet housing then replace just the housing. "Blocking off"/removing the control/assist hose will tend to not allow the valve to open at all and will reduce flow thus possibly heating even more.

So yes, since you're now double sure about H2O pressure, proper temp readings, timing and such now and if it were me, I'd be pulling the poppet valve too!! And if it still overheated, I'd remove stats and if it still overheated, I'd be pulling cylinder heads for a peek.....

My guess is poor water flow internal to the block or perhaps as Chris has thought, either way cylinder heads aren't all that scary, you'll be fine. They're just plates more or less with a threaded holes that holds spark plugs.

The heads I've pulled over the years and FWIW, be it 4 or 2 stoke, Al or cast, I reverse the torque sequence, stepping down in loosening force in several increments to as mush as possible minimize any warpage (is that a word?)

Don't sweat the 16 Volts yet, address the overheating first.

 

[sam am I]

If it's water flow issues, this additional info might help.....Do you know if the poppet is working correctly?

If you look real close at the H20 pressure you can usually see very subtle drops in pressure around 3K when the poppet opens.

If it's for sure working, as I think you've indicated/double checked already.........

I'd guess its specifically a "lower cylinder head flow" issue (The stats cooling/water path is probably okay still, green lines).......The red lines show the paths where the water in the cylinder head water exits at the bottoms of the heads and then out the through the poppet valve (call-outs 3 and 4).

The valve is open only at higher RPM's and that's where your overheating sounds and that is the primary cooling path that sounds like the issue due to overheating at high RPM. Removing the poppet valve and running should aid in trouble shooting (if it runs cool, your poppet is stuck, if not.......thinking blockage)

My guess, again if the poppet is okay, if you have a flow issue, is you have a plug/s restriction/s in the cylinder head port where it mates to the block and ports into and through the block around call-outs 1 and/or 2.

Still just a hunch though.......hard to say forsure without personally being under the hood.

 

[Dukedog]

At idle I have about 4psi and 18psi at WOT. Bob

this is pretty much right on... (3 ta 5 idle, 12+ wot)... if its gone up from 18 its either poppet, slight blockage or air.... your motor is '86 model without tha bleed hose goin' down to tha poppet... you "still" need ta put all new stuff, housin', ride plate, impeller, gaskets in tha pump no mater how "little sand" ya think went thru it!.... even if it all still "looks" new...tha pump can make pressure but lose volume ...... jmo

 

[sam am I]

when I hit about 5000rpm the water pressure was almost 24 psi....

if its gone up from 18 its either poppet, slight blockage or air....

Agree, I also think that 24 PSI sounds a bit suspect/too high, Duke definitely has the number on those blocks and if yours reflects anything close to mine, as the data suggests, I never ran over 15 PSI

So, thinking we're on the right path still

 

[CharlieB]

Poppet valves have a replaceable 'seat'. If this comes lose the valve cannot open correctly to allow full flow and cooling at high RPM will be reduced.

Disassemble and carefully inspect the poppet assy. If any doubt, order the replacement parts and follow the directions to replace.

 

[bobrock123]

OMG... I love you guys... OK.... today i started taking the exhaust cover plate off to check for anything... found some sand in the bottom .... not much i will make sure everything is clear there... i see alot of water ports ... I will make sure they are all clear. as for the electrical.... the stator I put in is a 16 amp. this engine did not come with a regulator..... so I bought a rectifier/regulator and wired it in.... apparently it had a like 9 amp stator before ... guess it never needed a regulator... I intend to use alot of wattage so the extra amps will help.... as for the overheating...... I replaced the poppet set and assembly.... I did see poppet movement on the pressure guage a few times... So what you are saying is..... if I take the poppet valve OUT..... I will get full flow thru the block? I thought water went thru the block first and when pressure overtakes spring pressure..... the poppet opens discharging water out of the block..... I will let you know how the exhaust plate effects the engine. asap....

 

[bobrock123]

OMG... I love that flow chart diagram ....... Thank you so much guys for trying....

 

[bobrock123]

I can't wait to say to you guys what the final problem was..... But I am learning so much.... this is no doubt a gremlin.... an anomaly..... so not typical especially with all the available info....

 

[sam am I]

So what you are saying is..... if I take the poppet valve OUT..... I will get full flow thru the block?

Correct

I thought water went thru the block first and when pressure overtakes spring pressure..... the poppet opens discharging water out of the block.....

Correct and if you remove the poppet(valve/spring assy)., the red line water flow can now freely flow through call-out 3 to 4 and will always discharge at any RPM......Therefor at high RPM's (where you stated you overheat), if it runs too hot still, the poppet valve (the removed one) is NOT the issue. The antithesis will be the engine begins running colder/normal at high RPM's indicating the poppet (the removed one) is/was malfunctioning.

 

[bobrock123]

So today I pulled the exhaust divider and cover plate... found a little sand .... cleared all ports.... I pulled the poppet valve out and ran it full flow... it was a little better