'87 XR2 150 HP high water pressure at idle and higher RPMs

[CWKboat]

Greetings,

I have an '87 Black Max 150 HP and have a Sterndrive Engineering lower unit (have used it 5 years with no issues). I recently changed the impeller as routine maintenance, but am concerned about high water pressure at idle and higher RPMs.

At idle on the muffs at 1000 RPM, I'm getting 14 PSI with cooler water coming out of the telltale. I have the "tee" fitting with one line coming down from the 2 t-stats merging into the tee with one line going into the lower block and the other one goes to the telltale. With an IR thermometer check, the block is barely getting to 100 degrees on the muffs and the top of the block is cool to the touch. I did take the t-stats out (new last year) and tested them and they opened and closed as they should.

At higher RPMS, I'm showing about 20 PSI at 4000 RPMs and over 30-35 PSI at 5000 RPMs (I quickly backed off). I do not have a temp gauge or working overheat alarm to my knowledge, so I've always relied on the water pressure gauge. This engine has never run over 15-18 PSI before at WOT.

I checked the poppet valve and it wasn't sticking, dirty, leaking, or clogged with debris. At idle in the driveway, there is water coming out of the prop steadily at idle, but seems possibly less than in the past.

At this point, I assume something is restricting the amount of water exiting the powerhead. Should I pull the powerhead and check for any debris in any of the exhaust outlets?

If so, what gaskets would I need to purchase? Would I also need to pull the heads and check for any debris in there or the block?

Thanks for any thoughts or advice!

 

[Dukedog]

has it done this all tha time since tha impeller change or start sometime after?.. I would revisit tha pump base, plate, housing and gaskets just because!!!.. i've screwed tha pooch on occasion myself!... jus sayin'


if its that high and steady at whatever pressure (not fluctuating which indicates air) its definitely a restriction somewhere in tha motor or adapter plate... 150 2.0 or 150 XR4?.. can get ya part numbers for adapter, power head and head gaskets if needed....

 

[CWKboat]

Thanks for the reply! It is the 1987 XR2 150 HP.

As I mentioned, it is a Sterndrive engineering aftermarket unit. Interestingly I changed the impeller for the first time 2 years ago with a Sierra impeller only and at that time did seen an increase in the idle water pressure as it went up to about 8-10 PSI. The WOT PSI stayed at no greater than about 15 PSI then and all of last season and I could tell the poppet was working correctly because I could see the PSI drop and slowly build back up past app. 2000 RPM.

I decided to change the impeller last week as this past weekend would be the first time taking it out this year After changing the impeller last week, I then saw even higher idle PSI as noted at about 14 PSI, and then also at higher RPMs as noted at 35 PSI+.

Maybe since it's an aftermarket lower unit, I should get the complete rebuild kit from the manufacturer just to eliminate that variable. I can plan to replace the gaskets/plate/housing complete kit to your first point and see if that helps. If that doesn't help matters, I can update and then look at pulling the powerhead.

Thanks again!

 

[Dukedog]

yeah, ya have something goin' on.. good idea ta check with sei.. pressure should be 3 ta 5 at idle and 12 ta 18 at wot with oem stuff... don't see much sei stuff in our bunch.. most everyone here surfaces their gear cases.... gl with it.

 

[CWKboat]

I ordered the complete water pump kit from SEI and will redo the entire assembly just to be sure. If I need to pull the powerhead, do I need to take exhaust cover off as well along with the heads and powerhead to access all of the water passages? Just looking ahead at what gaskets I would need to purchase.

Will keep posted, thanks!

 

[CWKboat]

To update, I did replace the complete water pump assembly upper and lower with no change in the high pressure at idle -- still about 14 PSI. I am waiting on the poppet parts to arrive to replace the poppet assembly.

Just FYI, I checked compression and all 6 are 110-115 PSI.

I wonder if I may have exhaust entering the cooling system and causing the high pressure at idle? I went ahead and have ordered the powerhead base gasket, head gaskets, cylinder cover gaskets, and exhaust divider plate gaskets and seal as I've decided to just pull the powerhead and inspect what going on and look for blockages.

Do I also need to replace the gasket on the bottom of the exhaust plate (the one on top of the driveshaft housing #33) which is Merc # 27-991772

 

[CWKboat]

One more quick question re: the exhaust plate/powerhead base gasket: Mercury shows both 27-997761 and 27-8231422


I ordered 27-997761 which is the cheaper one. Can you use either one? Or 27-8231422 for high performance applications? I haven't pulled my powerhead yet, so I'm not 100% sure which one I have, but am hoping the one on the way (27-997761) will work.

Serial # is OB169260 and i know it's an XR-2 because of the sticker on the flywheel.

Guess I'll find out soon enough, thanks for any confirmation!

 

[Dukedog]

tha cheapee will work if ya careful with it.. it will tear easily... # 33 goes "between" tha two adapter halves.. you will also need # 26.. should be all ya need.....

one very important thing ta do when ya split tha adapter plate is tha cleaning of tha two motor mounts and tha mount "pockets".. also tha hardware (nut, two washers, bolt) that holds 'em place.. it can and will leak if mounts or pockets wore and/or dirty..

 

[Silvertip]

You are risking an engine burn down if you are relying on the water pressure gauge to tell you the engine is overheating. Fix the alarm. Water pressure is just that -- it tells you the pump is working. It does NOT tell you if the engine is being cooled properly. That's what the alarm is for.,

 

[CWKboat]

tha cheapee will work if ya careful with it.. it will tear easily... # 33 goes "between" tha two adapter halves.. you will also need # 26.. should be all ya need.....

one very important thing ta do when ya split tha adapter plate is tha cleaning of tha two motor mounts and tha mount "pockets".. also tha hardware (nut, two washers, bolt) that holds 'em place.. it can and will leak if mounts or pockets wore and/or dirty..

Thanks for the tips with cleaning everything! I went ahead and ordered #26 and also #37 just in case. I also decided to cancel the el cheapo powerhead base gasket order and go with the more expensive one.

 

[CWKboat]

You are risking an engine burn down if you are relying on the water pressure gauge to tell you the engine is overheating. Fix the alarm. Water pressure is just that -- it tells you the pump is working. It does NOT tell you if the engine is being cooled properly. That's what the alarm is for.,

Thanks, will do. I'll need to order a new sender as the existing one's wiring has corroded. Will have to check my wiring harness diagram from the control box to figure out which wire plugs into the sender as it wasn't connected when I bought the engine. I recently replace the control box, so should be no worries on that side with the lead for the alarm.

 

[CWKboat]

tha cheapee will work if ya careful with it.. it will tear easily... # 33 goes "between" tha two adapter halves.. you will also need # 26.. should be all ya need.....

one very important thing ta do when ya split tha adapter plate is tha cleaning of tha two motor mounts and tha mount "pockets".. also tha hardware (nut, two washers, bolt) that holds 'em place.. it can and will leak if mounts or pockets wore and/or dirty..

Also have a question about the order of operations: Can the exhaust cover and the divider plate gaskets be removed and changed with the powerhead still on? It looks like there's a small clearance with the bottom of the exhaust cover and powerhead base. Just making sure.

Thanks again

 

[Dukedog]

should be easy with clam shell cowls... jus pull tha bracket off.

 

[CWKboat]

Thanks again, Dukedog.

I hope to start on it this weekend depending on if the various gaskets arrive. I also ordered the overheat alarm sender per Silvertip's point as mine was inoperable. I'll post the results when done.

 

[AFR Engines]

CWKboat did you get this figured out?