can i use 15w-40?

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May 30, 2002
Can i use this in my 1992 5.0 liter 4bbl? My manual says to use 40w if 50f+, or 30w at 32-50, and 20w-50 below 32. There is no mention of 15w-40. I always use 30w. Was there a 15w-40 in 1992? Why is it noy listed? I feel it would be too thin (15w) when hot. Am i right in thinking this?
The owner's manual on my 92 3.0L specifically says use a 30 weight and specifically says do not use multi-weights, but after my experience with a straight 30 passenger car motor oil this season I am going to a 15w40 universal oil and will feel far more comfortable with start-up and operating temp protection, however I will be changing it often. As I have discovered, there are far more factors to consider with marine use than with automobile use. Your 92 5.0 is still the basic engine design in use today and a multi is being recommended. May I suggest that you do a UOA with any oil mid-way through the season to see what is happening.
It is interesting that in a car the engine is a 05w/ or a 10w/ 30 oil . The advantage of straight 30 or 40 is there is o chance of deposits from viscosity improvers and dropping out of grade as marine use is brutal on the engines look at the u.o.a's . Caterpiller recommends straight 40 in their marinized engines for deposit control . Again 15w/40 h.d. oil works good in my experience.
When in doubt I always reach for a 15W40 in my Chev engines. But...I bet that the engine oil operates at far higher temperatures in the hull of a boat than in a car, truck or tractor trailer. How do VI improvers work when the entire lubricant is at a very high temperature is anyones guess. Most industrial engine applications use mono-grades. There are some very good SAE 30s and 40s of late with high VIs, such as Mobil's 1640 and 1630. These oils will flow far better when cold than the old 100 VI offerings. I look for flash points in the 250-270C range. My rule of thumb is high flash points for hot operation, high VI for cold pumping and flow engine oil performance. The flash point is the temperature where an oil is producing enough vapor to sustain an open flame. Volatility, is the evaporation tendency of an engine oil. It seems that when VI goes up as in multi-grade engine oils, the volatility goes up, and the flash point goes down, making those lubricants less suited for extremely hot operating temperatures.
I think using a machanical oil gauge is your best indicator of what is the best viscosity, I have tried several weight's in my jetboat and determined SAE 40 performs best (less pressure drop on an extended high rpm run), I saw a dramatic pressure drop even with 20w50, which tells me the oil is thinning when really pushed (heated). For an I/O boat 15w40 HDEO is probably fine, but for jets I would strongly recomend SAE 40, reason is that jets are 20-25 less effcient and work that much harder, but again try different weights and let your oil pressure gauge guide you, I like to see 8-10 psi oil per 1000 rpms on a hard run.
[Cool] Marine engines use a lower temp thermostat than car engines because most of them have raw-water cooling systems. That doesn't necessarily mean they'll run cooler all the time, but it's worth noting. I plan on getting a boat either next year or the year after (I have a jetski now) and although people at my dock are all old-school and stay away from synthetics, I'll probably run Mobil 1 15w-40 if and when I get one.
My old bayliner with a 4 banger volvo says to use 10/40. Thats what its been running with since 1986. I tried a few other weights but i didnt see any change for the better on the pressure gauge. Ford made awesome marine engines. If the manual says 40 wt then give it a try before you go to a multi weight oil. Mono grade oils dont burn off as much as multi's. A gm 3.0 is prone to use a little oil. Cant say why, that is just their nature. You can try different brands to see if you notice an improvement or bump up to 40 wt. Always replace your water impeller every 3rd year in any boat guys. Dont wait for your temp gauge to tell you something is wrong because then its too late!
Originally posted by userfriendly: How do VI improvers work when the entire lubricant is at a very high temperature is anyones guess. Most industrial engine applications use mono-grades.
I guess the quality of the VII's along with the amount used comes into play but when highly stressed the 15w-40 below sheared right along with the others . The 5w-40 Shell faired a bit better .;f=9;t=000104
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