[Fr. Frank]

I ran a '91 XR4 on my Seafari for six years. I had 135* thermostats installed in place of the original factory stats which actually opened at about 148-150.

I also moniter water pressure constantly. I also had a water temp gauge AND a cylinder head temp gauge for each cylinder head. (Not my idea, actually. The man who remanufactured my motor installed those.)

Result was fairly constant water temp of about 140* while on plane, regardless of how hard I ran it. More than once, I pushed 5200-5500 rpms for more than an hour of constant running, and temp still hung at 140. In contrast, the temp would rise to 145*-150* at idle to 1200 rpms, while maintaining 7-8 lbs of water pressure.

The poppet valve is vital to maintaining proper water pressure, which leads to proper temperatures. Doesn't matter how good your thermostats are if you aren't getting enough water flow to properly cool the engine.

I would do the following, in order:

• Check the Poppet valve for proper installation.
• Check thermostats for proper opening and closing
• Check water pressure. (should be 6lbs minimum to 18 lbs maximum)
• Check/replace water pump impeller and check water pump to inlet tube mating.
• Run motor for 1/2 hour in mild acidic solution in closed system (in a drum or tub) I use 1 gallon of muriatic swimming pool acid in 25 gallons of water.

Let us know.