Diesel won't get hot + white smoke Yanmar 3QM30

[odonnellryan]

Hey all, story time.

Bought boat recently, diesel ran fine with no smoke but it seemed to be getting hot. We ran it for a long time to move the boat: probably about 10 hours of motoring at around 2k to 2.5k rpms.

Kept an eye on things while running. At the thermostat temps did get around 200 degrees near the end of the trip.

However, high temps did cause a crack to open up in the coolant line causing us to lose coolant. Obviously not good.

All the hoses were basically shot. Like, if you tried you could put your finger through some. Fuel lines... I'm really surprised they were not leaking or letting air in already.

So I just got done replacing my fuel lines, fuel filters, and coolant lines (fresh + raw). Was a job but absolutely worth it.

At first it did actually overheat, but that was because of some air in the coolant lines. I was able to remedy this.

I had a hell of a time bleeding the engine, first time through. Eventually I did get the hang of it, but only right before I cracked one of the "bleeder bolts" on top of the injector. Oh man.

So the thing was still intact and I was able to remove it and replace it. Cool. Put the new one on, bled it out, engine started right up - with some white then dark smoke for a few seconds.

Then it ran without smoke in the slip OK. I put it into gear for a few minutes in the slip and did not notice anything wrong.

Except the damn thing would barely get above 100 degrees at ~2.2k RPM.

Took the boat out to put around and break it in more, after about an hour of motoring, half of that nearly with the throttle full open, I can only get it up to about 160 degrees!

Problem is, when the engine is lower RPM, let's say 2k or so, there's a slight white smoke (I think) but hardly noticeable.

At closer to 3k, there's a lot of smoke, so I didn't want to run it at that RPM for a very long time.

Another issue: might be my imagination but I think the engine "lost" some RPMs. As in, I feel I could get it to 2.8 or 2.9k at the start, and near the end of the test drive I could only get it up to 2.4 or 2.5k max throttle.

Also, before this change the diesel was clean or seemed clean! After, I noticed gunk in my fuel filter!

So questions:

1) Low temp is probably caused by thermostat, yeah? I can replace that I'm sure without too much trouble.

2) Think I completely fudged the engine somehow?

3) I feel the white smoke can be due to a clogged filter (since I notice "gunk" in the one). I'll replace this first.

4) Maybe white smoke compounded by low heat?

5) What do you think the chances are of a piece of that cracked bolt causing mayhem on top of the injector while not making the damn thing not work at all? I don't think it is missing any pieces but...

6) Max RPM issue seems to be a concern, right? I feel I remember seeing if your engine doesn't get up to the rated throttle or close to it (I think 3.2k for this engine) it's "really bad."


Any other thoughts? Engine does start right up and idles fine. Before this it would seem most happy at about 1.2k RPMs but would not stall until under about 8k (about where I shift) and that hasn't changed.


Thanks all. Sorry for the book but tried to include as much as I remember.

[odonnellryan]

Note: one thing I did NOT do was test the RPMs out of gear. Now that I think about it, I have a "feeling" that maybe the prop is too big. It is a hell of a prop and old, might be time to replace it.

[Pete7]

First thing I would check, is there a thermostat in the engine? you don't know what the previous owner has done. If you are going to do that, may as well replace it with peace of mind.

I would also check the fuel tank for gunge if your new filters have some signs.

What is the engine and what is the recommended operating temperature?

The revs could be down to a fouled prop or bottom if it hasn't been done or cleaned recently.

Pete

[jkishel]

Running below normal operating temperature (180 degrees F) is commonly caused by a stuck open, or missing thermostat. It's a good idea to verify actual operating temperature with a cheap infrared thermometer (sending unit, gauge and/or wiring could be bad).

White smoke is unburned fuel, black smoke is partially burned fuel. Black smoke at high rpm under load is often caused by an oversized or fouled prop and/or fouled bottom.

[CarlF]

The hoses being that bad suggest the PO wasn't great on maintenance.

Change the thermostat just because it's so cheap, why not? Buy two so you have a spare.

Use an IR thermometer to check temps. Odds are quite high that the gauge or sender is also bad given it's age

2500 rpm is not great but it's not likely hurting your engine (assuming you get the temp back up). And your tach may be wrong too. For less than $20 you can check it by getting a "laser" tach that works off a bit of shiny tape you put on the crank pulley.

Replacing the hoses was a good idea. Here are some things worth thinking about (although probably not related to your current problem):

1) How old is your fuel? If more than a couple of years worth pumping out

2) V-belt (if you don't know how old it is, worth replacing anyways and buying a spare)

3) Battery - if over 5 years old worth replacing since you can bet the PO didn't take care of it.

4) Prop - many boats have oversized props. Whether or not it hurts the engine it definitely slows your sailing speed. Think about investing in a folding prop or a low drag fixed prop like the Campbell Sailer prop. The boat will sail much better.

5) Battery cables - Replace if they look bad. If they are OK, remove and clean the connection points and put on a contact grease to protect them. Be sure to do this at the engine including the engine ground cable.

[Dsanduril]

White smoke is unburned fuel (as noted above) which can come from compression problems, timing problems, injection problems, and a few other less likely causes. With compression it could be glazing/scoring in the cylinders/rings which might be cured with a chemical clean.

But, 'white smoke' can also be steam, especially if present at high load and not really present at low load/idle. You can tell the difference by how the 'smoke' dissipates. Steam disappears pretty quickly as it gets away from the boat, real smoke should be visible for a while (although it depends on amount). Steam results from reduced raw water flow through the HX and into the mixing elbow (assuming it is that type of exhaust). Since all the other rubber parts were in bad shape have you checked the raw water impeller? And yes, you can have a cool running engine with enough raw water flow to keep the coolant system OK but still not have enough water to cool the exhaust gas stream to the point that there is no steam.

[DeepFrz]

Junk in your fuel filter means your tank/tanks need cleaning.

[davecalvert]

We had the white smoke issue on a Volvo 55. Changed all filters but, still the white smoke, even at low RPMs. When putting my hand in the smoke, there was no smell. So, didn't think it was unused fuel.
The water output looked low so I changed the impeller, no difference.
We than disconnected the water line at the sea cock from the sail drive. Very little water was coming out. We used a stiff plastic tube to run down through the sea cock and water began rushing out. Connected the water line, started the engine, no more smoke. This was steam caused by a low water intake.

[sainted]

A lot of good advice here. Second (or third or fourth) replacing the thermostat and the impeller.

However, as a happy Yanmar owner and a marine mechanic I can tell you that many Yanmars smoke a little. You don't really quantify how much smoke its making. Can you not see the back of the boat? Could you mask a Marine beach landing? If it's just a light mist, I wouldn't worry. It's a diesel after all.

To the notion that white smoke is unburned fuel, that could be, and it could be caused by a too aggressive prop or one that is badly fouled. If the engine can't reach its rated rpm, it would be sucking in too little air but injecting fuel as it it was running at the wot rpm.

You may want/need to descale the heat exchanger at some point as well. We circulate Rydlym in the engine's raw water system for three or four hours, which cleans all the coolers (oil, raw water, transmission) with out having to take them off the engine. That's really handy if the components are hard to get to. You'd have to hire that out though. The circulating pump is a bit pricy.

Good luck. Let us know how you make out. Yanmar's are good little motors. With a little care it will last for years.

[CarlF]

I read your post again:

You don't want to be getting anywhere close to 200 degrees. Most boats run between 170 and 180. If you are seeing 160 that could just be a slightly faulty gauge or sender. But replace the thermostat anyways and see what happens.

If the filter is clogging with gunk quickly, have the fuel pumped out. It's very common to have gunk grow in tanks if they aren't kept clean by adding some biocide when you fuel. You may need to have a professional clean the tank but at a minimum, carry a lot of spare fuel filters (like 6). A partially clogged filter is probably the 2nd most common cause of not reaching maximum RPM (1st is dirty prop or over-propped)

If it was black smoke at full RPM that is likely carbon burning off and unburned fuel from being overloaded from too big a prop. This isn't something you need to panic over. In time, the smoke will reduce as some of the carbon burns off. Always take the engine up to full RPM for 10 minutes a day to burn off carbon. Also, I've been told before shutdown to advance the throttle to full momentarily while in neutral three times to blow out any new gunk. Wait 30 seconds for the turbo to spin down (if you have one) and shutdown.

Agree with replacing the raw water impeller. Good thing to do every year. Certainly every other year. I'm betting the PO hasn't changed it in many years.

[NYSail]

Old Yanmar that wasn’t taken care of.....
I would definitely change thermostat and also check the mixing elbow.

Good luck

[Wotname]

Originally Posted by odonnellryan

Hey all, story time.

Bought boat recently, diesel ran fine with no smoke but it seemed to be getting hot. We ran it for a long time to move the boat: probably about 10 hours of motoring at around 2k to 2.5k rpms.

...........................

Problem is, when the engine is lower RPM, let's say 2k or so, there's a slight white smoke (I think) but hardly noticeable.

At closer to 3k, there's a lot of smoke, so I didn't want to run it at that RPM for a very long time.

Another issue: might be my imagination but I think the engine "lost" some RPMs. As in, I feel I could get it to 2.8 or 2.9k at the start, and near the end of the test drive I could only get it up to 2.4 or 2.5k max throttle.

.............
6) Max RPM issue seems to be a concern, right? I feel I remember seeing if your engine doesn't get up to the rated throttle or close to it (I think 3.2k for this engine) it's "really bad."


Any other thoughts? ...........

You max RPM is a concern (but not in the way you are thinking).

The max continuous rated RPM for this engine is 2,600 rpm and the 1 hour max is 2,800 rpm.

This suggests to me that you are driving the engine too hard and this will contribute to the overheating issue and likely the smoke aspects.

From the manual...

[Wotname]

^^ the QM series are tough workhorses and pretty hard to kill, their rated RPM is much lower than other small Yanmar marine engines and possibly one of the reasons they last so long.

Note the piston speed is only 7.8 m/sec at max continuous power.

[Cadence]

I might change the temp. sending unit. I have little faith in sending units temp. and oil press.. A temp. one will not brake the bank but may give you peace of mind.

[Wotname]

As others have posted, check (or better - replace) the thermostat and see note 4 - this matches your symptoms!