1985 Crusader 454 ch350 and 2015 Kohler 7.5ekd genset oil

[ron54]

Read as many oil posts as I could before asking these questions.

Previous owner used Royal purple 10W–30 HPS in motors, motors have about 1560 hours each. Probably a good idea because of the higher zinc content in the HPS but I think the 30 weight in our hot summers is a little thin. Boat would never run below 45 degrees F. I have pretty much decided to go with Rotella 15w-40 just not sure which one. The GEN set calls for 10 W – 30 when any temperature is below 50°. He gave me about 7 quarts of the Royal purple, may use that in genset, the Kohler oil specified for this advertises added zinc so assuming these are flat tappets. Generator only has 322 hours. Not sure what oil is in it now, was done by local service shop. No record of what oil.

Anyone see a problem with either one of these oils for the described? Also anyone have recent numbers as to the zinc and phosphorus content of the different Rotella oils. Hopefully they’re all above about 1200 which should be fine for these motors I believe.

Thanks

[plittle2005]

It has more to do with engine temp than ambient. For FWC, t'stat should be 160 F. Engine temp. then 160-170. use 15w-40.
For Raw water cooled, t'stat should be140, engine temp 140-150, use 10w-30.
Use Rotella T4. Shell publishes Zn=1200, P=1100.

Google this phrase: shell rotella t4 zinc content

[ron54]

Very good point thanks. When I got this boat on May I noticed it was running cold, port maybe 105
F in 80 degree water, starboard about 120. Pulled both thermostats and they were stuck partially open. Service records indicated in 2017 that they thought maybe both thermostats had been removed but nothing was done surprisingly. Only about 50 hours since then. I replaced with 142s but thinking I may go to 160s. The boat i s in very clean fresh water. Seems there is a school of thought that this is better in fresh water, no salt to precipitate. Thoughts?

[km1125]

You still have a bunch of other minerals that can precipitate, but just not the volume as in saltwater. Think about how much buildup you get just in a home water heater that uses city water (and worse with well water) after it's been run for several years!

160 is better for engine combustion... a bit more efficient. I don't know that anybody has actually measured an improvement in MPG though, between the difference of 160 vs 142/143. Higher temps are also a bit better for the oil, as it helps keep any condensed water from staying in there too long. It also helps vaporize any fuel that makes its way down to the crankcase.

[bud37]

Source of the post Very good point thanks. When I got this boat on May I noticed it was running cold, port maybe 105
F in 80 degree water, starboard about 120. Pulled both thermostats and they were stuck partially open. Service records indicated in 2017 that they thought maybe both thermostats had been removed but nothing was done surprisingly. Only about 50 hours since then. I replaced with 142s but thinking I may go to 160s. The boat i s in very clean fresh water. Seems there is a school of thought that this is better in fresh water, no salt to precipitate. Thoughts?

Ron how are you planning on using your boat, on trips will you be on plane the entire time or using it more like a trawler ?

Just to be sure ......you are raw water cooled right, no antifreeze.

[ron54]

Mostly at trawler speeds, very little on plane. Yes raw water cooled.

[Midnightsun]

All combustion engines run happier and more efficiently at higher temperatures. The only reason one sees 140 degree thermostats in boats is that salt will crystallize at higher temps leading to issues in a salt water applications. The norm for fresh water applications or closed systems is around 180F. All my previous boats had 160 stats in them and registered 180f on the gauge. My diesels run at 185F

[bud37]

Source of the post Mostly at trawler speeds, very little on plane. Yes raw water cooled.

Based on that, 160 stats are a good choice.......the engines will be happier with higher head temps, maybe help with exhaust gases as well.

[ron54]

I’ve been on the road so kind of slow to respond, thanks for all the good advice. Very much appreciated.

I am planning to switch to 160 thermostats, probably next spring and try it for a season. Table Rock lake is very clean and considered to be pretty “soft” water for a lake.

Also will switch to Rotella at end of season. I don’t see any problem with the Royal Purple HPS, reported to have zinc as high as 1700, probably overkill for Crusaders, I think it caters to the hot rod market with high lift flat tappet cams. I will be changing oil every year. May send samples of the Royal Purple for oil analysis to see if they find any issues.

What oil filters do you use? These have the horizontal mounted filters at top back of motor.

Again thanks to all for sharing your knowledge.

[ron54]

Not trying to start another “which oil is best” thread but thought I would provide links to a couple of interesting things I found. First is a link to a Bob is the oil guy forum post where several virgin oil analysis results are listed. He doesn’t say what lab but results are from 2023.

https://bobistheoilguy.com/forums/threa ... es.367146/

Second is from the petroleum quality institute, most recent analysis are from 2020 but would think oil formulas have not changed much. Numbers are a little lower on zinc and phosphate from the first link but correlate for the most part.

https://pqia.org/heavy-duty-diesel-engine-oil/

Again, for what it’s worth.