1991 150XR4 Cooling Problem

[Jonesky]

I seem to have developed a cooling problem on a 91 150XR4. I had rebuilt the fuel pump and fired it up with the hose attached to make sure it was OK. I noticed there was no water from the pee hole after sufficient running time and the water pressure guage was reading just above 0. I rebuilt the water pump and started it up to test today. I am reading about 3 psi at idle. At first there was no water from the pee hole after sufficient time so I shut it off and let it cool. On the 2nd try I got sporadic water from the pee hole but the pressure did not come up when the engine was increased to 1500 RPM.

I removed the hoses from the thermostats at the top of the heads and steam was coming out. I could blow through the hose with one end attached to a thermostat so I know they are opening (a blow through the hose produced air/steam at the other thermostat. Anyone have any ideas as to what to check next?

Thanks in advance.

 

[sschefer]

Re: 1991 150XR4 Cooling Problem

20" or 25" shaft?

 

[Jonesky]

Re: 1991 150XR4 Cooling Problem

I'm doing this from memory but I think it is a 25". Serial # is 0D068399 (1150453LD) if that helps.

 

[j_martin]

Re: 1991 150XR4 Cooling Problem

Yer losing pressure, which can be caused by:

1. Pump failure, impeller, housing, base plate, or base plate gasket.
2. Delivery tube and seals at both ends. Mis-installed or damaged seals or tube.
3. Poppet valve stuck open.

hope it helps
John

 

[Dukedog]

Re: 1991 150XR4 Cooling Problem

Yer losing pressure, which can be caused by:

1. Pump failure, impeller, housing, base plate, or base plate gasket.
John

Even if you replace tha impellar (aftermarket=50/50 chance) you still might have an unseen problem with tha rest of tha pump parts. Change it ALL using only OEM parts when it comes ta tha coolin' stuff. It will be tha best money you can spend on tha motor.........

 

[sschefer]

Re: 1991 150XR4 Cooling Problem

If it is a 25", the water tubes were in two pieces with a plastic connector in between. These connectors can become brittle and something as simple as sliding in the lower unit can crack them causing a dramatic drop in water pressure. It is not common but it is a suspect given the description of your problem.

You should be able to get a look at it with a flashlight and a mirror. If that's o.k. then check the poppet valve diaphram. If it's ruptured it can cause water pressure issues.

When you changed the impeller did you maybe forget the key?

Did your impeller have a bronze insert bushing or was is all rubber?

Did you rotate the drive shaft clockwise as you slid the pump housing on?

Did you put the rubber washer in between the cup and housing where the shaft exits?

When you put the impeller on the drive shaft, did it slide on easily or did you have to coax it the last few inches? This question is regarding the condition of the last impeller, if it spun it likely left bronze residue welded to the shaft. That will cause the next impeller to egg shape, wear out the center almost immediately and render the keyway useless. In otherwords, it will slip badly. If this sounds familiar, clean up the bronze residue with a fine file and emery cloth and replace the impeller the rest of the pump wont be damaged.

 

[sschefer]

Re: 1991 150XR4 Cooling Problem

Even if you replace tha impellar (aftermarket=50/50 chance) you still might have an unseen problem with tha rest of tha pump parts. Change it ALL using only OEM parts when it comes ta tha coolin' stuff. It will be tha best money you can spend on tha motor.........

That's a very valid point! However, I do get aftermarket pumps. I get them from Bill Kelly over at http://www.maxrules.com/. He ships them out of Seattle for me and I have them a lot faster than going through Merc. The product is every bit as good as the Merc original product and does have the impeller with the bronze insert. Not like the cheap Sierra junk that's out of stock half the time.

If there's anyone out there that doesn't sacrafice quality to turn a quick buck it's Bill. Do a search about his business on iBoats and you'll find I'm not the first to say this.

 

[Jonesky]

Re: 1991 150XR4 Cooling Problem - SOLVED

Re: 1991 150XR4 Cooling Problem - SOLVED

I found the problem. It was a vapor lock in the upper engine. I removed the thermostats and primed with water (after the engine cooled, of course). She fired up and started pumping water normally.

Thanks to all who helped out with the suggestions and opinions.

 

[j_martin]

Re: 1991 150XR4 Cooling Problem

I wouldn't run without thermostats. You run the risk of damaging the engine.

Good ones should allow the block to fill normally.

hope it helps
John

 

[Dukedog]

Re: 1991 150XR4 Cooling Problem

I wouldn't run without thermostats. You run the risk of damaging the engine.

John

100% agreed....It has to have some kind of restriction to slow tha water down so it can do its job. Carry heat out of tha motor..........

If you had to fill tha block manually you still have a problem somewhere. Cooling systems don't "vapor lock". Its an open system. Even when tha t-states are closed there are smaller by-pass holes that allow any air to purge into tha proper place. It just might show itself at another time. Hopefully not at tha wrong time. There are several things that could cause this from tha water pump all tha way to tha adapter plate. Make sure your warning buzzer works..................

Still feel like its water pump parts. If your testin' on tha hose that could be tha problem also. Put in tha lake and test on tha trailer. Look for any leaks at tha base of tha powerhead and around poppet cover.