Should I switch oil type?

[allen]

As many of you know, I have a Lapworth-36. It has a Graymarine 4-112 engine in it that I had rebuilt about 10 years ago. I think the guy who rebuilt it just sprayed the rust with fresh paint and charged me for a rebuild but that is an exaggeration I would assume. But the reality is that I had it rebuilt so I would get an engine I trust and have had nothing but problems. One of the main reasons I had it rebuilt was low oil pressure and sure enough, the rebuilt engine had low oil pressure. I probably put maybe 10 hours on it a year so I am guessing certainly less than 150 hours on it at this point.

I ran it hard in the slip, testing another of the problems I am having with the damn thing, for an hour. At the end of the hour and at the cruising RPM of 1100 I had 25 pounds and at idle about 5-7 pounds. This is with 40 weight, which is what Dave said to use when I first got the engine back and complained about the low oil pressure. I have a mechanical oil pressure gauge because Dave didn't believe my electrical one. I had to get rid of the factory gauge setup because the tach broke right after the rebuild. Nothing but problems after the rebuild...

The other issues is that with the engine cold if I give it too much RPM the oil pressure drops to zero as I guess it is too thick to get back to the sump. That doesn't happen often but is a concern.

I tried to find data online on oil viscosity and ultimately just did a test on a couple of options myself. How long it took for oil to pass through a 1/8 inch hole.
30 weight 36 seconds
20-50 weight 58 seconds
40 weight almost 2 minutes.

I am looking to see if my thinking is on the right track or if I am totally out to lunch. Probably between.
Multi weight oils are rated as equivalent at 0 degrees and 100 degrees C. I care more about room temperature and 100C. From my test the 20w-50 should help my oil starvation at startup issue and be thicker at hot. Seems like the way to go. I have read that I should use motorcycle oil because of the transmission.

The oil I have been using is non-detergent and I have a little concern about switching to detergent. I change oil about every 50 hours minimum but it can be several years and do not have an oil filter because I didn't want to lose the pressure. Any concerns about switching to detergent oil? It is only 150 hours but it is 10 years. So not long but also long depending on how you look at it.

I should add that one reason I am thinking of changing to detergent is that I have had trouble with the #1 exhaust valve sticking. It has happened 2 of the last 4 times I started the engine. This might be because I am not running it as hard as normal because the water inlet casting broke and is presently held together with epoxy and I didn't trust it. It did OK in my hour test yesterday but does leak the smallest amount. Doesn't drip but just a wet patch that quickly evaporates. I said the engine has been nothing but problems didn't I?

So my question is should I switch from 40 ND to 20w-50 motorcycle oil?

One final thought. Joe, you were right.

[Jedsail]

May I suggest that 10W 30 weight detergent oil is recommended. The engine will receive immediate lubrication when starting cold, [the cold oil will be thin and flowing easily] and as the oil warms, it will thicken to 30 weight, due to polymers in the oil. Detergents will keep the contaminants
[ byproducts of combustion] from accumulating inside the engine, and will be removed during an oil change.

Adding an oil filter is highly recommended, check NAPA Auto for options. [ you can install a full flow type, or bypass type ] Note that a correctly designed & installed oil filter system will have very minimal restriction, and will not effect oil pressure inside the engine.

Have you considered cutting your losses and aggrivation by installing a good running takeout diesel engine? Joe DeMers

[Capn ken]

Delo is the best .change your oil annually .preferabbly before any major layup ,such as winter. Contaminants should not be allowed in your engine for more than 12 months and an oil filter is a great idea . best of luck .start saving up for a replacement ,better performance and greater reliability .think beta marine .

[allen]

I decided on 10-40 motorcycle oil. I picked motorcycle oil because it doesn't have the low friction additives that can make a clutch like my reverse gear slip and yet it is detergent which I hope will help my stuck valve problem. I figure that while my test of my 40 weight didn't have great oil pressure, it was good enough and I am very unlikely to run the engine that hard for an hour. The 10-40 should give me something around 30 weight at room temperature which should lubricate better than the 40 weight I have been using at start up. I should still get an effective 40 weight when hot. The other choice was 20w-50. If I find the 10-40 it too thin, I will just switch to that and see how it works.

I probably should have bought a modern engine 5 years ago when I did the rebuild. Actually what I should have done is nothing as I didn't really gain much from the rebuild. But at the time I thought for my use, which is typically 1/2 hour run at a time, that a gas engine would be more appropriate. The most I would every run the engine would be for 2 hours which I do about once every decade.

If I need to get rid of the gas engine, I will probably go electric.

Allen