'93 Ski Nautique 351 PCM Pro Tech Overheating

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?

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.

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.

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.

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

That boat shouldn't have the 160 t-stat. A 160 T-stat will put your temp at around 180 or slightly above which may be what you are interpreting as an overheat situation. It should have a 140 t-stat.

8122pbrainard wrote: Tim, You mechanic did a RWP flow check and it was good so I would say you can rule out impeller pieces blocking passages.

Pete, who's to say it isn't pieces from a previous impeller?

There is not enough information given about the nature of the overheat in order to give you very good advice. There are a LOT of things that can contribute to running hot. If you could tell us exactly how and when it tends to overheat, then we can provide better advice on what to troubleshoot. Specifically, does the temp creep up at idle (especially after running hard), or at speed? Regardless of the mode, circ pump failure and corroded cooling passages are possible, but pretty far down on the list of likely culprits. Its likely to be something much simpler, with a pretty straightforward solution.

8122pbrainard wrote: tsassman wrote: By the way if indeed a piece of an impeller is restricting a passage. Tim, You mechanic did a RWP flow check and it was good so I would say you can rule out impeller pieces blocking passages. Shoot the area around the temp gauge sender with a IR heat gun and make sure it's not a gauge sender issue. Has all the gauge wiring been checked for loose and or corroded connections?

When I pick it up this weekend I will ask the tech. about the plugs and timing.

tsassman wrote: M3Fan wrote: That boat shouldn't have the 160 t-stat. A 160 T-stat will put your temp at around 180 or slightly above which may be what you are interpreting as an overheat situation. It should have a 140 t-stat. As stated at top all wires and connections were checked. I am planning on buying a IR gun to test it when I get the boat home this weekend. Thanks.

I agree with M3Fan on the Thermostat. A 93 era boat would typically have a 140 (143 actually) T-Stat.

If someone did actually retro-fit a GT-40 Fuel injected engine in this boat, it may then call for the 160.

is a carb or efi engine?

I believe the 143 is correct for a carb engine and the 160 is correct for the efi engine.

as far as temp readings I would be friggin nervous if my engine ran at 180-190 degrees...
Mine runs 160, virtually all time...

I think I would verify the temp gauge first, and check the dash ground.

If that was all good then I'd replace the stat again with a balanced stat.

Then I would go for the acid soak. All the heat is produced in the head area, so I think a couple of applications of acid soak might clean things up.

Bob

I'm goning to take this down a whole mother road here, sorry for the new name, I can't seem to get logged in as myself.

So we've got the water flowing and the ProTec isn't going into limp mode, and the point everyone missed is the manifolds aren't hot. So the problem is the gauge not the cooling system.   It's always a god idea to have an IR thermometer around, pick up a multimeter while you're at it. First thing I would check is the voltage your getting at the battery, the to the dash, and finaly to the gauges. Before my last rewire when I added the buss under the dash I was getting 12.5 volts at the dash, but it dropped to 10 by the time it got to the other side. This caused havoc with the PP and most of the gauges were off too. I was running 180 to 190 most of the time. Once I got the wiring fixed I've got 12.4 everywhere I look, 13.7 with the boat running and everything on (lights, heater, blower, and bildge pumps). Its now running 155-160 with the 160 Tstat just as it always has.

Another possibility may be the kind of thermostat. I have had issues with the cheap basic thermostat from the autoparts store opening slowly and causing the temp to rise to uncomfortable levels. I had to watch this happen in a pot on the stove to figure it out. The auto tstat would begin to open at the appropriate temp while the PCM one would go full open at the right temp. The auto tstat was closed to 200 before it fully opened. I'm in the group that says 160 is OK, I've been doing it for years, makes my heater work better and even in 90 degree water in August my boat stays below 170. I know everyone here screams about it, but I run almost identical temps to them.

I forgot to add, look at that receipt carefully and decide if you still got a deal. Then, come here next time you have a problem and get it figured out then fix it yourself so you never have to get another receipt for having your boat fixed.

It's really not that hard, you just saved a couple of years worth of gas. UPS will bring that thermostat from SKIDIM to your door a lot cheaper than 150 round trip.