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Author	Topic:   1988 mercury xr4 150 over heats below 30 mph
don lonbeck	posted 09-08-2009 09:31 PM ET (US)         I have a 1988 baker tunnel hull with 1988 merc xr4 150,just this summer I have over heating problems. At 30+mph to full throttle temp 1/4to 1/2 at below 30 temp 3/4, have not heard warning beeper.have replaced water pump assy ,stats and cleaned and inspected poppit valve.the pea hole has a steady stream and at 3/4 temp I can put my hand in the stream,It is hot but I dont get burned.compression is 120+on all six ,water pressure at speed is 5 to 6psi,is this low.possible obstruction in cooling system? ANY HELP WOULD BE APPRECIATED
high sierra	posted 09-09-2009 02:21 PM ET (US)             don, I had a xr2 150 and got slightly high temps as well. The pop off system is part of the problem. At low speeds the engine relies on the thermostats to regulate the temp. There is an intermittant pee flow sometimes at the lower speeds as the thermostats open and close. At higher speeds the popoff goes open and there is increased flow of water to cool the engine. I have worked on this problem for a dealer as well. His solution was to remove the stats even though the engine ran rather cool. Plugs might foul sooner but no overheating. high sierra
high sierra	posted 09-09-2009 02:23 PM ET (US)             PS at higher speeds the water pressure should be about 25 to 30 lbs. 5 at idle is ok . high sierra
don lonbeck	posted 09-09-2009 07:47 PM ET (US)             ran the boat 2 weeks ago without stats same problem,3/4 temp below 30 mph .
contender	posted 09-09-2009 07:52 PM ET (US)             Sounds like something with the water pump, If you are going over 30 and the water temp is ok its because the speed is forcing the water in/up the engine. I would pull the water pump out and change it.
don lonbeck	posted 09-10-2009 07:41 PM ET (US)             will remove lower unit this weekend and inspect pump,I replaced the pump assy part # 18-3517 1st of year this is an aftermarket kit,anyone use this kit? any problems? I will check to see if I put something in the wrong place,have replaced impeller half a dozen times but this is my first kit.
contender	posted 09-10-2009 10:10 PM ET (US)             Not to sound critical but I would use/purchase a factory water pump (get the entire kit). I have found in some applications a non factory(after market) item does not have the exact tolerances as a factory item. Check your connections to the pump (tube) also. Why have you had to replace the impeller so many times? Good luck
don lonbeck	posted 09-10-2009 10:45 PM ET (US)             bought the boat from the original oner my best friend,he replaced the impeller every season and advised me to do the same,I know this boat from new,I know that at idle or low speed to expect temps up to 1/2.
seahorse	posted 09-10-2009 11:39 PM ET (US)             For some reason the 150 seems to have more mid-range overheat problems than the other models. Try the The heavy duty impeller #47-89984T4 for V6 engines. It has a brass inner hub, not a plastic hub.
don lonbeck	posted 09-13-2009 09:29 PM ET (US)             took lower ynit off today,pump and impeller look new like when I replaced them 3 months ago, took off one stat forced water through stat hole,lots of water comes out throug pump tube,tried the other stat hole same thing. Time to take to shop! Thanks for the help.Don.

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