Installed new water pressure gauge with T fitting but no pressure at WOT.

[Randy99]

Hi,
Hoping you can help me with my water pressure gauge. I have a 1989 Mercury 150hp black max. I followed the hose that goes between the two thermostats then down the block to a tee which has two smaller hoses one going to a 90 into the block and the other side goes to the pee hole. I installed the plastic tee near the pee hole and I get about 8 psi when going 6mph then when I get up on plane it drops to zero and never reads again until I slow down to 6mph or so. I'm assuming I have the tee in the wrong place, sounds like least resistant path. Could someone shed some light on where I should be attaching my pressure gauge hose? Thank you kindly.
Randy

 

[Chris1956]

Those motors have a poppit valve that opens at higher waterpressure, bypassing the thermostats.

Do you have a hose down the center of the motor in the rear? If so, pull it off the fitting on the bottom and see if she has water pressure at idle, on the flusher, or in the water. That should be the place for the Tee.

 

[Randy99]

Thanks Chris for the info, I do not see a hose down the middle, I have looked all over this thing and cant figure out where it hooks into. The original pressure gauge had the plastic line cut near the idle speed box behind the flywheel. There is about a 1/2" plug behind the flywheel, looks like it uses a 3/8" rachet to remove. someone told me that was it but I'm skeptical about that. Would need a reducer and what not. I'll see if I can post a picture when I get home.

 

[Dukedog]

There is about a 1/2" plug behind the flywheel, looks like it uses a 3/8" rachet to remove. someone told me that was it but I'm skeptical about that. Would need a reducer and what not. I'll see if I can post a picture when I get home.

that's tha right place for it. remove tha pipe plug and adapt down to tubing size..……….. ace hardware is your friend for fittings you'll need....

 

[Randy99]

Here is a pic on the back of the motor

https://www.iboats.com/photo/157547

 

[Randy99]

https://www.iboats.com/photo/157765

 

[Dukedog]

that may not be an '89?.. pretty sure to piece heads were gone by then.. there was also a cowl change that year.. might have been a few "hold over" clam shells but not very many...

move tha pressure gauge nipple up to tha top like stated above..... its reading "after" tha stats where its at now.. won't show actual pressure at any rpm.....

 

[Randy99]

Ok will do thank you very much, I appreciate the help guys!
Side note, I checked the serial number with Mercury and they stated it was a 1989 XR4.

 

[Dukedog]

gottcha.. is tha serial number on tha block or tha number on tha clamp bracket?.. what is tha number?..

on top near tha "pipe plug" should be a welsh plug.. looks like a freeze plug.. may or may not have tha serial number stamped in it also.. if its original it will match tha number on tha clamp bracket...​

'89 XR4 had one piece heads and a water cooled 40 amp system with a lift off top cowl..

look near tha top part of tha heads and should be a stamp.. a small circle with a number in tha middle.. should be 3 1/8 or 3 3/8.. there is also a build date stamped on tha block.. it will be at tha bottom of #2 cyl. on tha block half where tha block and crankcase halves split.. kinda right behind tha bend in tha timing arm.. will be 1/8" numbers.. m/d/yr. might be hard ta see but it is there...

 

[Faztbullet]

Looks like a 1988 2L with 16amp stator and clipper...Xr4 had small gearcase and different cowl

 

[Randy99]

Ok installed the fittings on top of the block like stated and she reads pressure perfectly now. Question I have is when running on the lake at 3200 rpm the pressure reads 6-7 PSI and then when I reach 4000 and beyond rpm I see about 13-14 psi. Is the lower rpm normal for the given water pressure or should it be higher?

 

[leonreno]

Yes, normal