1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

Hi guys
I just got a 1985 Skeeter bass boat today with a 150hp XR2 Black Max on it. It has what looks like a digital temp gauge that is broken and someone has added what looks like a plane jane temp gauge down low beside the seat. I didn't even notice it when I test drove the boat. The boat ran fine but I was only able to open it up for about three minutes because of the size of the lake. No beeps or warning buzzers went off.(If they are connected). The problem I have is as soon as the boat planes out the temp gauge starts climbing and goes to hot. As soon as you go back to idle the temp gauge goes back down.
I don't know if it is a mismatched gauge or of the motor has a cooling problem at high speed. It is shooting good out of the pee hole and the guy showed where he had a new water pump installed last year.
I have been reading on this site about thermostats and poppets valves on these engines. I have no problem with getting a manual for this motor, but my wife is expecting to go the lake this weekend. I DO NOT want to tell her that I just got a boat that has a problem and I don't want to damage the motor by running it hot.
If some of you folks can point me to the information I need to test the cooling system you would more than likely save my life or at least save me from a good old fashion beat down from my wife. I just cant get the repair manual here before this weekend. Thanks.

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

If it doesn't boil a steam bubble in the head and set off the alarm, I wouldn't worry too much about it.
You're cooling a 2.2 million BTU fire inside that thing with a 2 inch paddle pump. I'd worry if it didn't run on the warm side.

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

Dig gauges and manual gauges use different sending units. As j_martin said, if it isn't blowing steam pockets out the tattle tail its not overheating. See if you can find the right gauge for it. You might get lucky and they will have one on the shelves.

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

Test the overheat alarm. First ground the alarm wire to see if th ebuzzer sounds. Then see if the sensors ground at high water temp 190* or so. Next test the thermostats. They should open at 143*F or so. If this passes, replace/rebuild the waterpump and poppit valve.

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

Thanks for the info. I hate to ask this but where is the poppit valve and thermostats on this motor? I will test the alarm and sensor this afternoon. That is as soon as I can find it. I have the ability to fix it I,m just not sure of how the system works on this motor or where the parts are located other than the pump in the lower section. Thanks again for the info.

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

When standing behind the motor,look to the bottem right side of the motor, the cover of the poppett valve will appear in a shape of an 8. There should 4 boalts holding the cover on. Most mariners will have them in stock. Ask the parts man and he should be able to describe it better

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

Thermostats are on cylinder heads, one each. My Merc V6 has a two bolt cover over them with a hose barb on the cover. The Poppit is low in the bottom cowl on the starboard side of the motor. Some of those Mercs have an overheat sensor on one head and a temp sender on the other head. if they are wired together they are likely both overheat sensors.

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

The XR2 probably came with an overheat switch on one head, and a temp gauge sender on the other one. The one that connects to the tan wire at a terminal block high and aft on the starboard side of the engine is the OT sensor. They are not wired together and are not interchangeable.

There's 2 other wires on that screw. One is the alarm output from the oil alert module, and the third is the alarm circuit that goes up to the controls. Anything that grounds that screw will sound the alarm when the key switch is on, providing 12V to the alarm buzzer.

hope it helps
john

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

My gauge on my 87 150 XR2 does nearly the same thing. Goes right to 3/4 or so if I'm running it hard. I've tested the over-heat alarm via grounding and taking it out and putting it in hot water. It works. I just don't pay much attension to that, I have a great tell tale, and 15psi at WOT on my water pressure gauge. To me the water out the tell tale feels way hot, but honestly anything above 120? feels really hot to me so it SHOULD feel really hot. No steam, etc...

I'd buy a 0-30psi water pressure gauge and install that, it will tell you a lot of things about the cooling system. John (above) helped me a great deal chase my tail on this motor last summer, and no matter how much I worried or checked things over the gauge still does the same thing, and the motor is solid and runs flawlessly.

This is similar to the water pressure gauge I bought. They sell them here on Iboats.com as well.

http://www.amazon.com/Teleflex-Vect...NXTK/ref=sr_1_1?ie=UTF8&qid=1307486587&sr=8-1

Re: 1985 Mercury XR2 Black Max 150hp. I need some help with the cooling system.

Thanks guys that is the info I was looking for. The boat already has a water pressure gauge but I was so busy watching the temp gauge I never even noticed the pressure gauge. The last time I messed with a outboard motor was over twenty years ago and that motor was at least twenty years old then. All it had was a pee hole and then one large round hole that would start spitting water when the thermostat started to open. Thanks again for all the help!