Interesting (*&?!) engine cooling problem on a 1992 Excel V-drive...

[SANfan]

My nephew has a 1992 Excel, 351 Ford V8 that is exhibiting an interesting (to say the least) cooling problem. I was hoping that someone on here might have some suggestions.

The engine would run at 3K at the dock for extended periods with the temp at ~170, but out on the lake it would quickly (5 minutes or less) climb to 200+. This was an intermittent problem last year, so over the winter he:

• Replaced all of the cooling hoses (they needed it - several were leaking and all were cracked)
• replaced the raw water impeller (more on that later)
• replaced the thermostat (PCM OEM, 142-degree)

After this, we ran the boat down the lake for 20 minutes - temps hung below 180 degrees the whole time. However, when he came off plane, the temp gauge ballooned to over 200 degrees, then slowly came back down to a reasonable level.

I'm still thinking raw water pump, mainly because I've pretty much exhausted my knowledge.... Tore it back down, and the wear plate is heavily grooved. I worked on it for awhile with 400/600/800 and couldn't get all of the scoring out. Can't flip it over because the other side is worse (he bought the boat used in 2010). He spent time under the boat over the winter cleaning the hull, so I'm not thinking an intake obstruction, but I told him to check that as well. What do you think?

• A wear plate is ~$25, a replacement Sherwood Pump is ~$375. Would you pop for a wear plate & new impeller or just bite the bullet and go with a pump? By the way, the hour meter says 600 hours, I think that (and the dealer that sold him the boat) is lying.
• Strainer is clean, no known obstructions or kinks in any of the hoses.
• The proper hose was used when all of the hoses were replaced.
• No leaks anywhere in the system

Any ideas short of anatomical impossibilities are welcome....

Luke

[Chexi]

Are you positive that the dash temp gauge is working properly? Have you checked it with an infrared temp gun? Before spending any more money trying to fix the cooling system, I would confirm that you have a cooling system problem and not a temp gauge problem.

[TX-Foilhead]

Mine runs 160 to 170 all day long with a 160 thermostat. Thighten all hose clamps with a wrench and check to make sure the gasket is in the strainer and it has no hairline cracks in the bowl. Blades off an old impeler can usually be found under the thermostat check that if you haven't already. The side of the block is the only place I have found that will read the same as the temp gauge, everything else seems to be much cooler. Voltage is also a possibility, but I've never seen mine bounce up that much unless I turn the boat off for a few seconds and then restart.

[TRBenj]

Also check the strainer bowl for cracks, tightness and the presence of the o-ring. The symptoms described indicate an air leak.

If everything checks out, then I would look closer at the RWP.

[shag]

I second checking with an infrared gun. Some of the older gauges are known to occasionally get a little off. My older nautiques would usually run around 160....

[SANfan]

Thanks for the replies - going to give it another shot sometime this weekend and see if I can make any headway.