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I'm new to the forum and hoping to utilize the expertise of the community as I attempt to get a recently acquired 1994 Ski Nautique in good running condition. Prior to my rescue, this Nautique set for 15 years in a warehouse. The boat belonged to an older brother from Indiana up until October, 2024 when I moved it out to Arizona. The boat has the PCM 5.8 HO engine with throttle body fuel injection. After some basic maintenance and check out, I ran the engine on a fake lake and then took the boat out to a local reservoir in November for about 2 hours. I’m afraid the engine needs some significant attention before I can call this a reliable boat….but I’m a little unsure on the best path to take….
A little history on the boat.
It was purchased by my brother used in 1996 from a local boat dealer with an unknown (to me) number of hours on it. My brother's family used it each summer during their short boating season from 1996-2015. It has set unused since 2015 primarily stored in a warehouse.
The boat has 850 hours on the meter which seems to work fine. If the meter is accurate (and has always been hooked up), it was used around 40 hours/season over the 20 years it was in service before being parked in 2015 due to family member health issues.
Recent Maintenance and Diagnostics I've performed
1. Drained the fuel tank and added new fuel.
2. Changed the oil and added new 10W-30 oil.
3. Replaced the transmission oil.
4. Installed a new battery.
5. Replaced the spark plugs and ran a cold engine compression test (results below) before installing new plugs.
6. Replaced the lake water intake pump impeller.
Test Results
7. Started the engine using a "fake lake" water plunger. The engine idled a little rough and seem to "miss" as the throttle was increased from idle to 2,500 rpm and just wasn't as smooth as I would have hoped for. I could also not get the engine temperature gauge to move hardly at all even after running for 15-20 minutes. I suspected that the thermostat was stuck open. I pulled out the thermostat housing and the engine did NOT have any thermostat in it! All it had was a fixed washer plate that restricted the intake water only slightly. I installed a new 170F thermostat, restarted the engine and the temperature did come up and held stead around 170F.
9. Conducted a "Lake Test" in November, 2024 at a local reservoir. The engine started easily but was also rough on idle. The engine seem to run better at higher speeds and easily got up to a plane pretty easy. Got in the water with a wet suit and was pulled a couple of times on "old fashioned" water skis to put some "load" on the boat.
10. Noticed the engine seem to smoke a little (burning oil smell) while in the lake while idling.
11. Parked the boat from November until early this week giving it a "break" until this week when I decided to dive into the engine condition a little more deeply as the boating season can begin pretty early here in Arizona.
12. Started the boat engine on the "fake lake" plunger to get it up to operating temperature.
13. Conducted a leak down test on each of the cylinders with the readings in the "Test Results" table above.
Conclusions
1. The warm engine leak down test results and cold engine compression test results correlate pretty well except cylinder #6 which seems to have a much higher leak down percentage than the compression test would predict. I suspect I didn’t quite have both valves closed when doing the leak down test. The overall test results do seem to explain the rough idle and "miss" I experienced during engine acceleration conditions on the driveway and at the lake. .
2. The engine has valve leakage issues on cylinders #5 and #6. I'm confident the leakage is on the valves rather than the piston rings based on the leakage level I observed at the dipstick and throttle body.
Next Steps?
1. Pull the intake manifold and heads. Inspect the cylinders and measure them for any obvious wear. If the cylinders look OK, stick with a top end rebuild without disassembling the engine. Besides working the heads/valves, I would likely replace the timing chain and sprockets and replace the water pump and gaskets but that's about it. By the way, The oil pressure is good around 40 psi at idle and goes up nicely with engine rpm to well past 60 psi. If the cylinders look marginal or show measurable wear, then I'm more than likely looking at an engine removal and rebuild
I'm not real crazy about spending the money to do a full engine rebuild of course! I would likely do a top end rebuild myself as I'm comfortable with that level of repair. If the entire engine needs rebuilding, I would likely take it to a shop and fork over the $3,000 plus (just a guess).
2. Regarding the boat's intended purpose and use, I was planning on investing in a Wake Board tower, doing some minor interior upgrades like new stereo, speakers, USB ports, etc. and using the boat as a wake board platform for a 60 something year old Wake Boarder who likes smooth water
and as a general run around boat.
Does this seem like a reasonable approach? Any other suggestions?
Thanks for your suggestions!
A little history on the boat.
It was purchased by my brother used in 1996 from a local boat dealer with an unknown (to me) number of hours on it. My brother's family used it each summer during their short boating season from 1996-2015. It has set unused since 2015 primarily stored in a warehouse.
The boat has 850 hours on the meter which seems to work fine. If the meter is accurate (and has always been hooked up), it was used around 40 hours/season over the 20 years it was in service before being parked in 2015 due to family member health issues.
Recent Maintenance and Diagnostics I've performed
1. Drained the fuel tank and added new fuel.
2. Changed the oil and added new 10W-30 oil.
3. Replaced the transmission oil.
4. Installed a new battery.
5. Replaced the spark plugs and ran a cold engine compression test (results below) before installing new plugs.
6. Replaced the lake water intake pump impeller.
Test Results
| Cylinder # | Nov, 2024 Compression Test Result #1, psi | Nov, 2024 Compression Test Result #2, psi | Feb, 2025 Leak Down Test Pin, psi | Feb, 2025 Leak Down Test Pout, psi | Feb, 2025 Leak Down Test, % Leakage |
| 1 | 120 | 125 | 90 | 88 | 2.2% |
| 2 | 90 | 95 | 90 | 86 | 4.4% |
| 3 | 120 | 120 | 90 | 88 | 2.2% |
| 4 | 120 | 130 | 90 | 89 | 1.1% |
| 5 | 65 | 75 | 90 | 66 | 27% |
| 6 | 95 | 100 | 90 | 70* | 22% |
| 7 | 105 | 95 | 90 | 87 | 3.3% |
| 8 | 120 | 115 | 90 | 89 | 1.1% |
9. Conducted a "Lake Test" in November, 2024 at a local reservoir. The engine started easily but was also rough on idle. The engine seem to run better at higher speeds and easily got up to a plane pretty easy. Got in the water with a wet suit and was pulled a couple of times on "old fashioned" water skis to put some "load" on the boat.
10. Noticed the engine seem to smoke a little (burning oil smell) while in the lake while idling.
11. Parked the boat from November until early this week giving it a "break" until this week when I decided to dive into the engine condition a little more deeply as the boating season can begin pretty early here in Arizona.
12. Started the boat engine on the "fake lake" plunger to get it up to operating temperature.
13. Conducted a leak down test on each of the cylinders with the readings in the "Test Results" table above.
Conclusions
1. The warm engine leak down test results and cold engine compression test results correlate pretty well except cylinder #6 which seems to have a much higher leak down percentage than the compression test would predict. I suspect I didn’t quite have both valves closed when doing the leak down test. The overall test results do seem to explain the rough idle and "miss" I experienced during engine acceleration conditions on the driveway and at the lake. .
2. The engine has valve leakage issues on cylinders #5 and #6. I'm confident the leakage is on the valves rather than the piston rings based on the leakage level I observed at the dipstick and throttle body.
Next Steps?
1. Pull the intake manifold and heads. Inspect the cylinders and measure them for any obvious wear. If the cylinders look OK, stick with a top end rebuild without disassembling the engine. Besides working the heads/valves, I would likely replace the timing chain and sprockets and replace the water pump and gaskets but that's about it. By the way, The oil pressure is good around 40 psi at idle and goes up nicely with engine rpm to well past 60 psi. If the cylinders look marginal or show measurable wear, then I'm more than likely looking at an engine removal and rebuild
I'm not real crazy about spending the money to do a full engine rebuild of course! I would likely do a top end rebuild myself as I'm comfortable with that level of repair. If the entire engine needs rebuilding, I would likely take it to a shop and fork over the $3,000 plus (just a guess).2. Regarding the boat's intended purpose and use, I was planning on investing in a Wake Board tower, doing some minor interior upgrades like new stereo, speakers, USB ports, etc. and using the boat as a wake board platform for a 60 something year old Wake Boarder who likes smooth water
and as a general run around boat.Does this seem like a reasonable approach? Any other suggestions?
Thanks for your suggestions!
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