'93 Ski Nautique 351 PCM Pro Tech Overheating

tsassman wrote: Thanks, I'll put it on my list of things I might try. Still open for more suggestions if anyone has any. By the way if indeed a piece of an impeller is restricting a passage. What would be the solution there? Has anyone had any experience with that?

You've got to find it and dig it out.... Did your shop check timing? Just a thought, but an out of time engine will run hot,as will an overly lean engine.   What did your plugs look like? These may not be even close to the issue, but I wanted to think a little outside of the box from where the others have gone....   On a side note, I have heard that Coke is a great cooling system cleaner, I've always wondered if it works, but never had a vehicle I was willing to try it on

Would you suggest that I change the water pump out first to rule out that as the issue. If it isn't not much lost there right.

OK, I'll give it a shot. Mind you I haven't done this myself!

Pull out the thermostat. Remove the pump drive belts. Drain the block, both sides. Pour your solution in. Some science needs to be done on the solution, commercial boiler lime cleaner? Maybe ask a radiator shop? Maybe just 'The Works' toilet cleaner (which is acid). Run the engine for a few minutes at idle. After a soak period, maybe a day, put the thermostat back in, hook the belts up & a raw water supply. Run the engine, catching the rusty crud coming out the exhaust, or run it on your neighbor's driveway when he isn't home (just kidding Ralph).

This might be hard on the water pump, but your were thinking about changing it anyway.

Keep in mind this may not be the real problem - you could have chunks of an old impellar stuck in a passage somwhere - I can't help you there.

You might want to try some lime-away type cleaner (acidic) - pour it in & let it sit for a few days, then flush well. Maybe even idle the engine (belt off) for a couple minutes to heat up that soup.

I purchased a ’93 Ski Nautique (my first boat) a couple of months ago at a real good price. Before purchase we took a test drive and really the only issue was sporadic temperature readings. Boat owner said probably needs a new thermostat or gauge. I have all the original paper work from original owner with the original owner’s manual. Original purchase was in Dallas and I purchased it from a guy in Austin. As far as I know it has never seen salt or even brackish water. Don’t know how may owners it has had.

Took the boat to marine shop for a complete checkup (I noted to have him check the temperature issue) and here is what they have done:

1)     Battery – Check electrolyte level and specific gravity. Inspect case for damage. Inspect cable and connections.
2)     Change engine oil and filter.
3)     Change transmission oil.
4)     Check and adjust engine alignment.
5)     Clean and inspect ignition system.
6)     Check and inspect cooling system, drive belt, and exhaust system.
7)     Check electrical system for loose or dirty connections and damaged wiring.
8)     Clean and inspect flame arrestor and crankcase ventilation system.
9)     Check complete engine assembly.
10)     Replace fuel filter.
11)     Replace raw water impeller.
12)     Checked all hoses and clamps for cracks and leaks.
13)     Checked all temperature sensors.

His notes on the temperature issues after all this was he tested the boat on the lake and it overheated. He then pulled the thermostat and noticed a large amount of rust in the thermostat housing. He pulled the thermostat, cleaned out the housing and installed a new 160F thermostat. Boat was them retested with the same result – overheating getting close to 200F.

Technician then performed a raw water pump capacity test the result showing proper performance (5 gallons flowed in 15 seconds @ 3000 RPM’s) Circulation pump was now in question but mechanic contacted PCM support technician (Travis Snyder) to discuss issues. Both seem to think that the circulation pump could be weak but due to the manifolds and risers not overheating this is not the main issue. PCM believes that due to the rust issue at the thermostat and water jackets proper flow has been compromised. New circulation pump could possibly fix the issue, but may not be able to perform and better than a weak circulation pump to possible blockage in cooling water passages.

He said the engine might have to be pulled and taken to machine shop to have cooling water passages cleaned out. Sounds expensive!!!! Any thoughts or suggestions on what course of action I should take next?