2.4 200 HP High water pressure 45 PSI

**slpcamaross97** · 05-23-2019, 09:31 AM

Updated to help anyone else who has a similar concern. A lot of good info and posts for possible ares that could cause it.

My fix was a convex plastic washer for the poppet valve diaphragm along with the screw for the washer and poppet valve being bent about 30 degrees causing uneven pressure and allowing water to bypass around the screw and get onto the back side of the diaphragm.

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I did a ton of searching and did not find a similar issues.

Motor is 1986 Merc 200 HP black max. Recent buy. Twin Engine Boat, Only one engine has the issue. Fresh water engines

Issue is that the motor temp is running on the high side(Only have factory merc gauge without temp readings). Temp warning does not go off, but i wont let the gauge go to that point.

Water pressure is super high, When on plane and at 4,000 RPM pressure is 45 psi.(actually wraps the gauge up against the peg for 0 psi). I also found that the water pressures will follow RPM in neutral and bringing the RPMs up to 5k. (Can hit 30 PSI at 5k at the dock).

When I bring the RPMs down and keep the water pressure at a more normal range, the Engine temp is in a more normal temp when compared to the port engine(Twin engine boat)

Pressure at idle matches the port engine(Twin engine boat).

Poppet valves are the First design that do Not have the water hose running to them.

When i received the boat the motors did not have T-stats(now are installed). owner said the engine always seemed to run on the hotter side.

New parts currently include(Both motors)
T-stats & gaskets
Poppet valves, springs, gaskets, seats, gaskets and diaphragms.
Exhaust cooler plate remove/install with all new gaskets
Water pump kits, upper housings, gaskets (Lower housings were done in 2015 and looked good)

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Looking over the water flow diagram, and given that the poppet valve does not seem to be bleeding off the pressure correctly, it would seem like a have a blocked passage that would affect the poppet valves performance and normal water "exhaust/drain passages"? Would that be in the base gasket area? Any way to test this without pulling the powerhead? or ?

Or could this be a headgasket putting to much air pressure into the water system affecting it? Good way to test for that or prove it out?

Thanks all.

**rock** · 05-23-2019, 11:39 AM

As you thought you have a restriction. Probably in adapter plate (base plate). You will have to pull powerhead to be sure but high water pressure and hot under load are indicative. Before I did that however I would do a compression test to rule out head gasket cuz a blown head gasket can have similar symptoms. Good luck.

Rock

**Jay Smith** · 05-23-2019, 03:32 PM

I agree with Rock , high spent water pressure points to two possibilities
1. Spent water blockage leaving the block ..
2. Blown head gasket , but if it were a blown head gasket your pressure gauge would pulse every time piston would create compression ...

Like Rock said if you We not observing pulsing my bet would be tuner adapter plate crudded up ...

Jay

**Merc 2.5** · 05-23-2019, 03:48 PM

I have been texting slpcamaross97 and these r the same thing I've told him , he also has lw pickup and found sand in exh chest , so my money is on the plate stopped up

**slpcamaross97** · 05-23-2019, 04:09 PM

You guys are all the BEST! Im going to have to get some cool swag for all the brilliant minds! Ill offer up my services. I know all about VWs, Chryslers, Gm LS swaps, C10s.

**slpcamaross97** · 05-23-2019, 04:10 PM

I will update. Im about to leave work and drive home to start testing and part removal. These last few hrs at work have been a killer thinking about the boat.

**Merc 2.5** · 05-23-2019, 04:11 PM

We just a big family that likes help fellow go fast guys and just boaters period , without getting raped at a "dealer"

**Merc 2.5** · 05-23-2019, 04:12 PM

Originally Posted by slpcamaross97

I will update. Im about to leave work and drive home to start testing and part removal. These last few hrs at work have been a killer thinking about the boat.

This happens to me almost everyday Haha. Unless rainin

**Merc 2.5** · 05-23-2019, 09:02 PM

Well. Update for OP. Base plate full sand , prob should b fixed soon

**slpcamaross97** · 05-23-2019, 10:27 PM

Half the bottom of the lake here. I got a good feeling this is the issue.

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**slpcamaross97** · 05-23-2019, 10:29 PM

Originally Posted by Merc 2.5

We just a big family that likes help fellow go fast guys and just boaters period , without getting raped at a "dealer"

I'm willing to bet that the last owner took this to the dealer after distorting the impeller and they just slammed a new impeller in it and called it good.

**Merc 2.5** · 05-24-2019, 06:03 AM

I can bout guarentee it!! 90% ov em never do the job rite

**Jay Smith** · 05-24-2019, 06:40 AM

Drill those holes slightly larger and with a counter sink chamfer those dump holes makes junk leave better !!!

**slpcamaross97** · 05-24-2019, 08:31 AM

Originally Posted by Jay Smith

Drill those holes slightly larger and with a counter sink chamfer those dump holes makes junk leave better !!!

What holes are you referencing?

**slpcamaross97** · 05-24-2019, 09:27 AM

Parts are on order. They had the two mid plate gaskets in stock. But i also found the lower crankshaft main seal tension spring laying in the mid plate. So im playing it safe and installing new end cap assembly that comes with new seals.