Oil Analysis - Gas Engines

Due to flat tappets, as well as maximum bearing-coat protection I use 15W-40 Valvoline Premium Blue HD Diesel Oil and 4 oz of ZDDP (Zinc Dyialkyl Dithio Phosphate) in my good condition 1977 twin 350 cid / 255 hp Mercruiser inboard direct drives.* Annual temp range in engine room where boat berths 55f to 85f.* Also, if more than a day has elapsed between run times I bring oil pressure up twice for a count of three via starter alone before allowing engine to fire off and start.

When I change oil this winter, I plan to send samples of each gas engine in for analysis.* Therefore the oil will have the fullest extent of contaminants possible.*

Question:* For most accurate reading, is it best to send oil for analysis at end of usage span or in mid span?

Thanks, Art


-- Edited by Art on Tuesday 27th of September 2011 04:24:15 PM

DavidM wrote:
Pull your oil sample when you change it, at the end of its usage span.

But you need at least three samples to make any real sense of what the oil analysis is saying. Just looking at one sample won't tell you much. You need a trend.

David

Click to expand...

*David - Thinking of what you imply... I trend to think you correct!* TY for input, Art

While a good history of samples is really fine , a single sample can be a big help, as it could alert you to a disaster like anti freeze in the oil.

A decade of samples goes a long way in helping to sell a boat when the time comes.

FF wrote:
While a good history of samples is really fine , a single sample can be a big help, as it could alert you to a disaster like anti freeze in the oil.

A decade of samples goes a long way in helping to sell a boat when the time comes.

Click to expand...

*FF - TY for input... True on both counts!* Even though I feel*confident that both engines oil is currently in real good condition,*it will be interesting to learn actual PPM counts if/of any intrusions.* Interesting notion re decade of samples... re eventual sales as well as ongoing piece of mind.* You do that decade thing yourself?* I am fanatic in care of my mechanical systems on boats, cars, trucks... etc.* So much so that I virtually never take a vehicle out without checking all fluid levels and a gen visual survey.* I change fluids more often than most.* I learned early on that high-grade, clean, and full fluid counts in all sealed systems = best performance and mechanical longevity!* For joints, cables, interactive moving parts, springs and other items... WD40 is my friend!* **

"You do that decade thing yourself?"

Yes , the boat was sampled Before purchase , and about every 300since hours by DD lab.

With a 6-71 to take a compression test is really big bucks , probably a grand as the injectors need to be removed and then properly re-timed. Skilled folks and big hours.

When we finally sell the boat a fresh sample result , that will natch the results from "day 1" should make it easier for the purchaser to save that grand.

However , should he wish to change the boats power (now de-rated to 165/1800) the cost would be minor if he wants 235/2100.

On our new tow toy with a "Volvo" ( Chebby 305) and duo prop a sample was looked at before purchase , but for such a cheap engine probably wont be continued.