Is my Diesel Mechanic brilliant or a fool?

[fritz3000g]

I've been relying on the advice of a mechanic at the marina I'd like to store my boat at, but he said something today that made me question his judgement.

Some quotes:

It is not possible to conduct a compression test on a diesel engine but we can determine if it need a tune up or other service that would improve the motor performance. One test is to determine if the engine is reaching the max rpm range according to the specification. This will give us a starting point.

My Response to him: I'm confused by your statement that you can't compression test a diesel. Are we talking about different things when we use that term? I've attached the pages from the Yanmar 1GM service manual which detail how to perform a compression test. I'm told it's harder on an engine without glow plugs but still possible.

Let me rephrase it. I won’t be able to complete a compression test. We don’t have any of the fitting or high pressure gauges. In the last 10 years we have not run across the need to complete this test on diesel motor. I find the diesels go from good to bad in a hurry. Last year we encountered 2 perfectly running diesels that failed due to parts failure. I prefer the leak down test if the engine is not running and then I normally bring in an engine rebuilding to investigate the issues.

The thing that made me question his judgement is the statement that you can't do a compression test on a Diesel motor, which you clearly can. The service manual said that you should do a compression test at the start of every tune-up.

He seems to be saying the following as well, which I'm now second guessing:

• Testing that the engine reaches max RPMs is the best test you can do on a diesel engine.
• Diesel engines fail very quickly after showing low compression, so there's no point testing compression because the window where there's low compression in a running not-yet-failed engine is very short. I'm assuming "failed" means not running rather than unfixable. I've heard him say before that diesel engines with moderate hours seldom fail so as to be unfixable.
• A leak down test is the best way to diagnose issues on a diesel that isn't running (meaning can't be run?).

So my question is, is this person not really a mechanic (meaning that the marina isn't really a diesel repair shop), or is he just sloppy with words in email? Is he right about the bullets I've listed above?

So far he doesn't appear to be playing any angles to make money off me. The only angle I can figure is getting me to service my boat at his marina, so that if the engine does fail I'll buy a new one from him. He is the only Yanmar dealer in town, though there are others closer to my home.

[JD-MDR]

I had a one cylinder ysm12 for a while . My mechanic used to always make fun of me cuz I would get so worked up about things like compression, valve timing, governor adjustment and all those things that are part of tuning up a gas engine. If a one cylinder diesel engine starts then it has good compression especially if it starts right away. If it doesn't get the RPM's then the fuel is not perfect.. Clean the filters, lines and tank . Then take the injector to be serviced. The injector pump and other things don't get out of adjustment unless they've been tampered with... that is just what I gathered form my own experiences

[ghockaday]

Testing compression is not something I would do as a yearly check up. What he is saying rings pretty true.

[Frenchy]

As far as diesels "going from good to bad in a hurry", my last motor - a Universal 5424- was running pretty good
with no issues other than a little black smoke now and then when it suddenly locked up. When I turned the key,
the starter motor just clicked and hummed. When I threw the compression release and tried to turn it over by
hand and couldn't, I got worried. As a last resort I removed the starter hoping that maybe the starter motor
was locked up to the flywheel somehow. That didn't work either.
So yeah - in my case, the motor did go from good to bad in a hurry. - Jean

[fritz3000g]

]If a one cylinder diesel engine starts then it has good compression especially if it starts right away.

If it doesn't get the RPM's then the fuel is not perfect.. Clean the filters, lines and tank . Then take the injector to be serviced.

Thanks! I'm also trying to figure out which parts of my experience with gas engines translate to diesel. I'm also pretty neurotic about them. Given the cost, the stakes are very high. It makes me want to micromanage the engine, and is weird to hear that you can't.

Thanks!

[sgbernd]

I have owned and driven diesels for much of my life (Peugeot, VWs, Dodge, etc.) and had marine diesels. Never once have I had or heard of doing a compression test, although I know they are possible and see them mentioned in the service manuals. The previous writer is correct in saying "if it starts, compression is good".

I suppose it is possible that the valves are burnt or rings worn but in practice, it is nearly impossible to accumulate that many hours on a boat used recreationally. An industrial or agricultural engine can but we just don't get that far.

Finally, it is a huge pain to measure and any results are subject to interpretation at best. To measure the compression, you need to remove the injector(s), inject some oil to seal the rings, and get a high pressure gauge which fits into the injector hole. This is much harder than using the spark plug threads in a gas engine. Then, when you get a result, you argue about if it is meaningful because maybe the engine was cold, starter weak, battery tired, etc. Finally you have to bleed the fuel lines to purge the air which you introduced when removing the injectors. Sometimes they have a compressable copper ring to seal them which need to be replaced.

The most difficult time for a low compression diesel is a cold start at high altitude. If you can get it started cold, relatively quickly depending on if it has a glow plug or not, without resorting to starting fluid, block heaters, or other tricks, you are good. If not, there may be a problem.

Steve

[tjr818]

Fritz3000g,
What engine do you have in the 25D? Our 27 had the Yammer YSM8 with 1200 hours. Our surveyor told us that the YSM8 is good for at least 10,000 hours if we change the oil and filters on a regular basis. The YSM8 is an industrial engine that is often credited with running 100,000 in Japan. No glow plugs and it always started, cold weather or warm.

[fritz3000g]

What engine do you have in the 25D? Our 27 had the Yammer YSM8 with 1200 hours. Our surveyor told us that the YSM8 is good for at least 10,000 hours if we change the oil and filters on a regular basis. The YSM8 is an industrial engine that is often credited with running 100,000 in Japan. No glow plugs and it always started, cold weather or warm.

I have the 1GM. It was produced starting in 1980, the year after the YSM8 was discontinued. It might have been a replacement. Do you have any information about the 1GM and how it lasts compared to the YSM8?

The one thing that the mechanic said about the old Yanmar diesels is that the tolerances weren't very high. For this reason, that they can continue to run for a long time even after parts have begun to wear out because they tolerate deterioration well.

I'm not sure to what extent it's true, but I have seen 1950s two-stroke gas outboards that still run with 60 lbs of compression, which is well below the compression modern engines require to start. Perhaps the same principal applies.

I have owned and driven diesels for much of my life (Peugeot, VWs, Dodge, etc.) and had marine diesels. Never once have I had or heard of doing a compression test, although I know they are possible and see them mentioned in the service manuals. The previous writer is correct in saying "if it starts, compression is good". I suppose it is possible that the valves are burnt or rings worn but in practice, it is nearly impossible to accumulate that many hours on a boat used recreationally. An industrial or agricultural engine can but we just don't get that far.

Here's the quandary. When I read books and blogs about sailing trips, I frequently hear stories of diesels failing when people need them most. If things like compression can't tell you how a diesel is performing, how can you ensure that your diesel is in good shape and won't fail when you need it? On my 5 hp gas outboard I know every component, could rebuild it myself, and can tell when things are starting to go sideways based on the sound, starting conditions, and I know how to debug issues before they're going to result in a failed start. I'd really like to learn how to do that with the diesel.

[JD-MDR]

Clean oil, clean fuel and coolant lines. Most diesels will run forever. Smoke and leaks are the signs that it needs attention

[fritz3000g]

Clean oil, clean fuel and coolant lines. Most diesels will run forever. Smoke and leaks are the signs that it needs attention

...If it doesn't get the RPM's then the fuel is not perfect.. Clean the filters, lines and tank . Then take the injector to be serviced.

Thanks!

Do you mean

1. Clean Oil, Clean Fuel Lines, and Clean Coolant Lines?
2. Clean Oil, Clean Fuel, and Clean Coolant Lines?
3. Something else?

... assuming you mean (2):

Clean Oil
Is there any way to tell if my oil is getting dirty prematurely? Would that cause smoke? Would running it through a coffee filter tell you?

Clean Fuel
Clean = Fresh, without air (in lines), without water, and without particles. Is that right?

I appreciated your directions above for how to determine this, and what to do about it

Clean Coolant Lines
For a seawater cooled engine, it seems like the flow of water through the engine at fixed RPMs would be a useful indicator of dirty coolant lines. Does that seem right?

I could try to catch all the coolant water in a bag or something and measure how long it took to fill up, or how much I got in 30 seconds. Is there a better way to diagnose dirty or clogged seawater coolant lines (assuming that's what you meant)

For anyone else reading this, this seems like a good post: https://learndiesels.com/10-signs-and-s ... el-engine/

[tjr818]

You can send oil samples to a lab, such as Blackstone, and they will analyze the oil, looking for metal deposits, oil contamination, higher than normal temperatures, etc. the first analysis is often revealing, but annual analysis will pick up trends and help with predictions. When I was flying we used to do this for all engines every 100 hours. For our 27 that would have been every seven years. We did it almost every other year

[JD-MDR]

Clean oil, clean fuel and coolant lines. Most diesels will run forever. Smoke and leaks are the signs that it needs attention

...If it doesn't get the RPM's then the fuel is not perfect.. Clean the filters, lines and tank . Then take the injector to be serviced.

Thanks!

Do you mean

1. Clean Oil, Clean Fuel Lines, and Clean Coolant Lines?
2. Clean Oil, Clean Fuel, and Clean Coolant Lines?
3. Something else?

All I meant was change the oil and filters often. I change the oil every 100 hrs., some do it after 50hrs.. I change the fuel less often maybe 200-300 hrs. I use one of those pumps that goes on a drill motor to suck the crud out of my fuel tank. I would pull the tank but it's really set in there. It's more work than I want to do right now. I've flushed out my raw water cooling system with a 7:1 ratio of muriatic acid and water several times in the 5 years I ve had this boat not to mention I took it all apart and cleaned the exhaust manifold manually and replaced all the old hoses, thermostat and water pump.
I've been very lucky with my 45 yr. old engine. It runs perfectly, doesn't use or leak a single drop of oil and starts immediately on the first revolution. Lets see how it holds up when I set sail around the N Pacific next Month. I will try to use it as least as possible just knowing how old it is.
OH... don't use cheap oil. I use Chevron Delo 400 for diesels

[ghockaday]

A diesel will not run forever if it is a saltwater boat that is raw water cooled. I could not compare the diesel in my 1972 tractor that has a radiator and clean coolant and sits in a dry barn to a Boat that sits in a salt water environment. My opinion is still that its the environment not the hours. As others have pointed out good maintenance, clean fuel, clean air and good compression it will run a long long time. Why do they quit at inopportune times. Algae and water in the fuel tank that sits too long, saltwater corrosion on wires and cables, saltwater rotting the engine from the inside (was my issue) and outside, oil never getting up to temperature to burn the condensate out of it. strainers getting plugged and running hot from time to time.

A day sailing boat with a diesel is hard on them. Better than gas by far. but starting and running 20 minutes to get out the slip, turning it off sailing for the day, starting running 20 minutes to get back in the slip is far harder than running up to temperature for a days work. A lot of wear is when a dry engine is turning over, before oil pressure comes up.

Just my opinion, but diesels are meant to work. The harder that work with proper maintenance, the longer they last. I have know truck drivers that never shut their truck down. (when fuel was cheap) unless it was going to sit for few days.

[Jack.Ducas]

Every thing Ghockaday commented is spot on. I own a 1982 CD30 with the raw water cooled Volvo MD7 in it. When I bought the boat in 1996 I had no idea of how many hours were on it. It started and ran ok. Fast forward 5-6 years. I started to see an accumulation of soot on the stern and the starting became more of an issue. When it did start I noticed it would smoke a little. This is a 2 cyl motor and I would hear 1 cyl firing until it got enough fuel into it to fire off the second cyl and then come to life pushing out even more black smoke. It's a sail boat, I lived with it for another 3-4 years. I was fortunate to have access to a compression gage (diesel engines require unique gages for this) from a Volvo certified marine mechanic 1/4 mile from where I worked. When I did finally get around to checking it 2-3 years later I found one cylinder was significantly lower than the other which is why I'd hear 1 cyl firing first. That's when I found a second MD7 and began a complete rebuild (1st over pistons, bearings, rebuilt injectors and high pressure pump) in my garage knowing things don't fix themselves. That motor sat in the garage for another 3-4 years while old smokey got worse. End of season cold starting here in the NE would take 30 to 40 seconds of cranking over. It still ran, I changed it out. I guess my point is old diesels will start and run for a long time. They use those old Volvos continuously in Sweden for irrigation pumps shutting them down only between oil changes. Hope this helps.

[JD-MDR]

"Will run forever" is just a figure of speech. We Californians kinda have our own lingo.