Merc v6 offshore 200 water pressure issue

[sutor623]

Hey guys,
I am dealing with a head scratcher. A buddy of mine has a 1997 200 offshore 2 stroke carbed motor. Serial :OG487642

Anyways, he brought it to me to look at. He had overheated badly enough to melt the main wiring harness to the block. The impeller was shot and all of the fins were long gone. No telling where they ended up. Compression was still pretty good, over 100 on all 6. We decided to put a waterpump, poppet valve, stats and a wiring harness and see how she did.

Took her to the lake and the water pressure gauge was reading 15psi at idle and well over 30psi at 1/2 throttle, and gauge completely pegged all the way to WOT. CRAZY!! Sure enough, after about 2 mins of cruising, overheat alarm start buzzing. We dropped it back to an idle and within 5 seconds the alarm cut off. So we came back in.

I inspected all water hoses and didn't find any blockages. We figured some impeller was in the block preventing water flow so we decided to pull cylinder heads and exhaust manifold. No debris. Pulled powerhead to check water tube grommet and see if exhaust gasket was melted and water was making its way straight out the exhaust. Didn't find any pieces of old impeller. Gaskets looked ok considering this was a saltie dog.

Soooooo, we pulled the stats and checked them, pulled poppet, blew air and ran a coat hanger through every water passage, took the line off the water pressure gauge and made sure it was clear, and put it all back together with new gaskets. (Wasn't done in vain because his steering arm was rusted to about the point of breaking so we replaced that while we were in there.)

Hadn't gone back to the lake yet, but the dang water pressure is still reading super high. I checked it with compressed air (while line is full with water) at 10lbs, 20lbs and 30lbs and it is reading properly.

Is it possible that the poppet valve (brand new) isnt opening? I am also not sure that the water pressure T went in the right spot (I didnt install it.) It is T'd int the line that goes from the top of the powerhead to the poppet valve.

 

[Faztbullet]

That should be a 2.5L motor and pressure will be 2-7 psi at idle and 18-25 at WOT...Sound like poppet binding...

 

[sutor623]

Thanks Fazt that's what I thought. What would cause this? All the components are new and cleaned up.......
Even with the old poppet it did the same thing.

 

[sam am I]

Perhaps something in here may help.........

https://forums.iboats.com/forum/eng.../10785014-mercury-xr2-150-high-water-pressure

 

[Dukedog]

does tha mid go with tha powerhead or has tha powerhead been changed?.. you still have a blockage somewhere.. with 15lbs at idle it won't concern poppet 'cause it's supposed to be closed anyway... gut tha poppet and run it if pressure stays high then ya absolutely have a blockage somewhere...it could be in tha "bottom piece" of tha two adapter plates?.. impeller pieces can get lodged anywhere and you not be able ta fnd 'em by sight or any probin' with whatever ya use...

 

[sutor623]

Well guys, thanks for all the input.

I figured out what happened. When we seated the plastic seat that the poppet valve goes into, we didn’t knock it in far enough. So fazt nailed it, poppet wasn’t opening because the seat wasn’t installed properly.

we knocked the seat all the way into the block with a 1” socket, put the popper back on and now she’s running at 3lbs at idle, 20lbs at wot and we put 10 miles on her today and she ran nice and cool. Crazy what 1/8” in that seat will do. I’d have never guessed that would be it.

i see a lot of these threads on here about high psi. I wonder how many have not installed their poppet seat properly. Mine was a very snug fit.

 

[Dukedog]

good for ya.. never seen an open (even justa tad) poppet cause "high pressure" but.............. did you "stake" tha grommet after you got it seated in tha block?

 

[sutor623]

So I don’t think that it was forcing the poppet open, I think that it was putting enough tension on the spring so that it couldn’t open or didn’t have room to open.

either way, I was surprised that it even changed my idle pressure (when the poppet isn’t even open). I don’t think the spent water was making it out of the block at the poppet valve.

 

[Dukedog]

its not supposed ta "open" till rpm and pressure comes up.. its supposed ta be closed below 1500 or so rpm.. that's why I don't understand tha 15 lbs "at idle".. under normal conditions its closed at idle with 2 ta 7 lbs.. pressure should drop with it open anyway ya look at it.. but it IS a merc so..... high perf. 245/260 doesn't have any sign of poppet assy. in it.. some straight outta tha box will show "0" lbs at idle and max of 7 or 8 lbs at grand plus... no mater its fixed with everyone and tha motor happy now.... gl from here on out.

 

[sutor623]

Thanks duke. I am a bit perplexed as well. The pressure gauge is In the line that comes from the powerhead and dumps into the poppet housing. If I took that line loose it read zero psi. Then I plugged it, and took another waterline and ran it off the poppet housing. The line off the poppet would not take any compressed air and it didn’t dump any water at higher rpms.

after I seated it properly water would dump out the poppet housing down into the block at low rpms and at high rpms water came out of that hose that was run off the poppet.

my theory is that the water pressure was high because it couldn’t dump out the poppet housing at Lower rpms.