water pressure?

[sawblade723]

What is the normal water pressure at idle for a '87 Merc 150 XR2. I just installed a new complete water pump and now I am holding 15 psi at idle. I have not run it on the water yet, only in a test tank.

 

[j_martin]

Re: water pressure?

What is the normal water pressure at idle for a '87 Merc 150 XR2. I just installed a new complete water pump and now I am holding 15 psi at idle. I have not run it on the water yet, only in a test tank.

Sounds pretty high. Either gauge wrong, or something plugged up.

 

[saumon]

Re: water pressure?

Should be more like 15-17 at WOT and 2-3 at idle

 

[sawblade723]

Re: water pressure?

I thought that was too high, I must have done something wrong when I installed the new water pump. Would a stuck poppet cause this to happen? Mine has never been changed.

 

[sawblade723]

Re: water pressure?

OK, I changed the poppet valve and now I have 25 psi of water pressure at idle. I pulled the water pressure tubing from the brass fitting on top of the block and water would shoot out 15 feet across the yard. The poppet and thermostats are not stopping the water from entering the block for some reason. The thermostats are new also and were working fine before the water pump rebuild. Where should I look next?

 

[Dukedog]

Re: water pressure?

Is tha motor gettin' warm? Not just tha water but feel tha heads and tha block around tha clyinders.......

 

[sawblade723]

Re: water pressure?

Yes, after about 5 minutes of idling the heads were starting to feel a little bit warm. The water from the tell tale felt like it was barely warmer than the tap water.

 

[Dukedog]

Re: water pressure?

Thinkin' that motor is just a plain jane type poppet without tha hose from tha top being a '87. So tha bleed hose ain't gonna come in ta play. If tha motor is gettin' warm and you KNOW tha warning buzzer is working, I'd take it to tha water and run it. Just moniter tha motor temp by hand if you have to. You should see a pressure drop a little above 2500 or so when tha poppet opens. But in your case it may not move very much at all. Watch for pressure irregularities like big fluxuations at a steady rpm, peggin' tha guage and etc. There may be a problem in tha adapter plate but don't think so.

Sometimes you get tha new stuff that has a lot better tolerance with parts that make a little more pressure, just never seen that much. Its uaually air that cause unusual high pressures but from tha intake on tha lower to where you are pulling tha pressure guage theres really no place to pull air in tha system except around tha pump and copper tube.

Try tha above and see what happens. Just take special care ta moniter tha motor temp...............

 

[j_martin]

Re: water pressure?

Thinkin' that motor is just a plain jane type poppet without tha hose from tha top being a '87. So tha bleed hose ain't gonna come in ta play. If tha motor is gettin' warm and you KNOW tha warning buzzer is working, I'd take it to tha water and run it. Just moniter tha motor temp by hand if you have to. You should see a pressure drop a little above 2500 or so when tha poppet opens. But in your case it may not move very much at all. Watch for pressure irregularities like big fluxuations at a steady rpm, peggin' tha guage and etc. There may be a problem in tha adapter plate but don't think so.

Sometimes you get tha new stuff that has a lot better tolerance with parts that make a little more pressure, just never seen that much. Its uaually air that cause unusual high pressures but from tha intake on tha lower to where you are pulling tha pressure guage theres really no place to pull air in tha system except around tha pump and copper tube.

Try tha above and see what happens. Just take special care ta moniter tha motor temp...............

I sawed a rotten log in half with the XR4 one time, and it behaved like that and also overheated.

I had to pull the t-stats, poppet, exhaust cover and divider and clean all the shredded wood out of the small passages inside.

Someone here will post a water routing diagram. I'll try to explain it. The water pump puts water into the block. Different passages route some of it through the heads and out the base plate, some through the t-stats and out the base plate, some out small ports in the bottom of the block and through the base plate, ans some through the poppet above about 2500 rpm and through the base plate. The bit that goes out the tattletale is insignificant.

Normally, enough escapes the open ports at idle so the pressure is about 4 or 5 lbs. As you rev it up, at about 13-15 lbs the poppet will operate and the pressure will lower a bit in a step, maybe 2 lbs. then as you speed up it'll ramp up to a max of 15 or 20 lbs.

Has it been worked on? Is it possible it has the wrong base or base gasket in it?

hope it helps
John

 

[j_martin]

Re: water pressure?

I guess Duke has a lot more 'sperience than me, but I've never seen air make pressure in a hydraulic (water) system. The copper tube is under pressure. If it leaks, you lose pressure in the block and water runs out all the wrong holes, like the shift shaft hole in the LU.

hope it helps
John

 

[sschefer]

Re: water pressure?

I think Johns on the right track with this. I have a 200 block under my bench that's full of gravel. There are some small but necessary water passages and if they were blocked I could see where pressure would be high. These impellers are tall and short winged which means they're high pressure/low volume. If you picked up a hand full of sand/mud at the sand bar and ground the impeller down you could have also plugged up the block but didn't notice it because the pressure didn't change.

The new impeller is now pumping a full load and with the blockage your pressure is way up and your motors getting warm.

Do you have a backflush fitting at the bottom of your exhaust divider plate. If you do you might be able to flush it out.

 

[Faztbullet]

Re: water pressure?

If your water pressure guage returns to zero when engine is off I doubt its the guage. If your fitting is in the top of block and pressure is that high you have a blockage in the exhaust divider plate passages. The older poppit system (without the feeder hose) should run 17-25 psi @ 5000 rpm and 2-7 psi at idle. The newer poppit system(feeder hose) is a pressure system and helps open the poppit earlier in the rpm range that why Merc spec's give 12 psi min @5000rpm and 2-5 @ idle. Did the engine get hot or any of the impeller blades missing?

 

[Dukedog]

Re: water pressure?

Yep John ya got me! Sometimes my fingers don't esplain' zactly what I intend for 'em to.........A large amount of air leak (intake holes completely outta tha water) in tha system (or steady water leak) will cause a pressure loss but an erratic injection of small amounts will cause funny, erratic and sometimes a big jump in pressure at tha guage. Don't know if thats any better but I'm tryin' :redface:...........

 

[Faztbullet]

Re: water pressure?

I have seen exactly that on the early Johnrude loopers, we popped 4 engines in a week period. The OMC rep came in and looked them over and said they where getting hot. What was happening.... We had then on a Hydra-Sport tunnel bass boat and when you got to 65-70 mph the tunnels where adding lift and at full trim air was entering water intake. This caused block to over heat and seize/scuff pistons and the water pressure guage would only flucuate 3 or 4 psi and buzzer never went off. The fix was a 2nd Effort low water pickup gearcase as stock case if lowered on jack plate caused to much bow lift...

 

[sschefer]

Re: water pressure?

The newer poppit system(feeder hose) is a pressure system and helps open the poppit earlier in the rpm range that why Merc spec's give 12 psi min @5000rpm and 2-5 @ idle. Did the engine get hot or any of the impeller blades missing?

Thank you for that statement.. Makes me feel better that I acutally figured something out on my own and wasn't foolishly sticking to my guns.

FB do you happen to know if anything changed in the poppet valve itself (spring, diaphram, etc.). You might have read that I had a buddy that removed the feeder hose and the valve beat the grommet out of the block and was working on the seat. I'm not discounting that the poppet could have been installed wrong in the first place or that some other force like him running with his jack plate too high could have been a contributor.

I was running mine without too, but after I saw that I put it back on. He had a distinct rattle but I've never had one. At least not as loud as he said his was.

FYI, I don't think this hijacks this thread since we don't know what has been done to this engine and this may be something that needs to be checked out.

 

[Dukedog]

Re: water pressure?

The newer poppit system(feeder hose) is a pressure system and helps open the poppit earlier in the rpm range that why Merc spec's give 12 psi min @5000rpm and 2-5 @ idle.

You real sure 'bout this. We saw this change when tha adapter/divider plates changed in '91. Ya know when Merc had a continous 1 1/2 year "brain fart". We thought that was tha reason since tha '89 and '90 had tha hose and tha same pressures as earlier non hose motors. Thought tha hose mighta been just one of tha reasons for tha divider plate change................

Fb, I know its hard ta believe but Mercs will burn down to when that happens.......................

sschefer, all tha "new" design which are tha 4 bolt type, with or without tha hose bib, innards are tha same......at least ta '98, '99 I think. Maybe even longer................

 

[Faztbullet]

Re: water pressure?

We had a big discussion on this one day on why rectifiers where failing when the rep was in the shop. He called a engineer and this is what I wrote in my service notes..
Plate and poppit changed to to improve cooling to rectifier ,increased volume thru block. Rectifier is regulated system with imput of 18-20 volts from stator and can reach up to 200 volts at rpm and does not bleed excess to ground but it sits there untill regulator outputs again. Rectifier temps can reach up to 130 degrees in certain app's. The flat plate on the front of windings is a shunt plate to sheild coil from the large magnets,acts as shorted winding to reduce voltage.
This was the 89-91 years that had the "hunk of s**t" 1 piece rectifiers, and the divider plate (1 piece) did drop w.p as it increased flow to heads. I been doing this since 1974 and have forgotten a lot....:redface:
I will call my buddy at the factory and get refreshed tomorrow..

 

[Dukedog]

Re: water pressure?

Thats kinda what we were thinkin' to but tha '89 and '90 had tha early 2 piece divider plate and pos water cooled regulator. Divider plate changed ta one piece tha same time tha adapter plates did in '91. It don't mater anyway. Just like gettin' my old remaining 2 brain cells a workout sometimes.........

I left out a key word in tha other post. Should have been adapter/divider
I fixed it.................

 

[sschefer]

Re: water pressure?

sschefer, all tha "new" design which are tha 4 bolt type, with or without tha hose bib, innards are tha same......at least ta '98, '99 I think. Maybe even longer................

At least to 99. The 200 I have has it. I took my 91 135 out for a spin yesterday. It's got the 4 bolt. I never had the 0 pressure problem after a WOT run. That could have been a fluke but whatever the cause, it didn't return after I put the "Whatcha ma callit" tube back on.

Just a FYI - I've found some pretty good evidence that the change occured in 90-1/2. From what I've seen, most of the 90-1/2's are commonly refered to as 91's. I think that was a mid-year crisis for Merc because there were more changes that came about in 92.

Sounds like hair splitting but when you look at the two and try to order parts it makes a difference.

 

[Dukedog]

Re: water pressure?

Just a FYI - I've found some pretty good evidence that the change occured in 90-1/2. From what I've seen, most of the 90-1/2's are commonly refered to as 91's. I think that was a mid-year crisis for Merc because there were more changes that came about in 92.

Yeah, It depends on tha date of production. Usually if it was built in tha 6th or 7th month its referd to as tha next years model.........................