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

[odonnellryan]

Lots of great replies here. Thank you all so much.

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

This is good to know. Thank you. I assumed it was higher. In neutral I'm almost certain the engine will get up to 3k+ if I want. Is this a problem? Or just a matter of don't run it that high?

Re: thermastat. I actually have a few spares left from PO. He had quite a collection of parts and things for a lot of the boat, but I feel his mentality was far in the "don't fix what isn't broken!" category. Mine has always been to fix before it breaks to the extreme, but I've been trying to reign that in just a bit!

Mixing elbow is thankfully new. BUT. There is play there that needs to be fixed. It is not super tight.

Re: temps, it was 200 before I replaced lines and ran new coolant. I figured this was hot.

I'm measuring the temp two ways:

1) new sender to a digital readout. This is actually about 5-10 degrees off from:

2) Hitting the outside of the housing for that sender with an infrared temp reader.

Is this the correct place to measure temps? Seems to make the most sense to me. I imagine the coolant is a few degrees hotter than what is measured.

Impellers: I inspected them.

I've bought a cheap but nice DC fuel pump that I will use to flush the tanks and use old fuel in a diesel furnace for hot water. Regarding this, what's the best process?

I was thinking of a way to "aerate" the tank to stir up all the gunk.. but that might be too complicated. Maybe just empty, then slosh some fuel in, empty again, etc?

> 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).

This is an amazing note, and you know... honestly it didn't really smell that bad. Might have just been normal exhaust smell. However, from my memory... it did seem to disappear somewhat quickly!

So time to check the raw water throughput. It seems to have good flow visibly, but might just be clogged up.

Also, the mixing elbow is loose. Can probably use another rotation to tighten if I can manage. The (new) CO detector right next to the engine doesn't go off though, so I was making the gamble that not many fumes were getting into the boat.

But I wonder if this could cause steam?!

Belts, wiring, batteries, etc.. are all really good suggestions and are absolutely on the list to replace.

Thanks a lot all. I'm going to check the raw water impeller first, as that should be checked or replaced anyway. Then replace the thermostat, and from there we'll see what's up!

Missed a few comments!

> 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.

It's not a ton. Around 2k RPMs it really isn't very noticeable. Higher RPMs absolutely, but now I am starting to think it is steam! I was paying attention the first time we ran the boat (for about 6 hours daylight and another 6 in the dark) and during the daylight hours I didn't notice any smoke.

> descale the heat exchanger at some point as well.

This is a great suggestion and I'll put this on the list. If it seems really bad I'll just replace the thing. I'm sure it's old.

> The circulating pump is a bit pricy.

Hmm! A regular DC pump for coolant connected inline wouldn't work? My heat exchanger is not hard to remove anyway. Accessible and 2 screws after you disconnect the hoses.

I feel the PO was good at some things. Impeller definitely. He has even kept the old ones (not bad condition) and has plenty of new.

Re: oil pressure... I'm sure this isn't working at all. Light does not come on when turning the key. Needs to be addressed.

[Pete7]

What sort of access do you have to the fuel tank? is there a nice big inspection hatch or if not, would you be willing to fit one given your approach to maintenance.

Pete

[Mike Banks]

White smoke is usually unburned fuel. Check your timing as well as the other things you are already doing. Some engines need glow plugs to get them started in cold weather. A dud glow plug may mean one cylinder not firing properly, if you are using glow plugs. Cold diesel engines never run well. They need to be around 180 degrees Fahrenheit.

[Wotname]

Re white smoke and steam.

All engines create steam and mostly this isn't seen, It only becomes visible when it condenses immediately after leaving the exhaust and that needs cold ambient temperatures and often still air.

So you see it most on cold calm mornings and you rarely see it on warm days or when there is any breeze. By cold I mean less than 10C.

[Wotname]

Originally Posted by odonnellryan

..........

Also, the mixing elbow is loose. Can probably use another rotation to tighten if I can manage. The (new) CO detector right next to the engine doesn't go off though, so I was making the gamble that not many fumes were getting into the boat.

But I wonder if this could cause steam?!

........

It won't cause steam (see above post) and you will know if it leaking badly because you will smell it way before the CO detector does. BTW, diesels don't generate that much CO but the detector is still a good idea.

Note, they do produce some CO but the strong smell of the other gases give the game away.

[SAMUELBURNS]

Yanmar engines are famous for plugged exhaust system resulting in excessive back pressure to exhaust gases. The usual culprit is the mixing elbow, which you can remove [ sometimes easier to remove attached exhaust housing to engine ] clean with multiple soaks in muriatic acid [ $10 /gal at Lowes - be careful to ONLY pour the acid into water . . . NEVER water into acid ]. A thick black liquid discharge from the mixing elbow will confirm the carbon buildup problem. Less back pressure will allow engine to run at full throttle and at normal operating temp.

[Cheechako]

Sometimes it depends on how the temp is measured. For instance, an air lock in an engine may cause the temp gauge to not read hot at all, (air at the sensor) while the engine is burning up!
Other issues can be impeller chunks in a heat exchanger from impeller failure and subsequent replacement without getting the pieces removed.

[Symphony]

Does anyone replace their thermostat annually? that was mentioned in the manual snip kindly posted by Wotname: replace annually or every 2,000 hours.

I run about 150 hours annually.

[thunderhoof]

Although not Yanmar-specific I found an issue keeping an older Yanmar diesel from running properly. The fuel line from the tank under the settee ran about 6 feet aft to the fuel filter. I found it clogged from deposits due to the lack regular biocide treatment. Replaced hose / used biocide - no further problem.

[Cheechako]

Originally Posted by Symphony

Does anyone replace their thermostat annually? that was mentioned in the manual snip kindly posted by Wotname: replace annually or every 2,000 hours.

I run about 150 hours annually.

I have never done that, Yanmar or not.

[Compass790]

Originally Posted by Symphony

Does anyone replace their thermostat annually? that was mentioned in the manual snip kindly posted by Wotname: replace annually or every 2,000 hours.

I run about 150 hours annually.

Yanmar loves it if you buy a thermostat annually. Ours is 3.5yrs old & counting...Similar usage to you. You can remove & test if you want & also it should be apparent if it fails. We carry a spare.

[Wotname]

Hmm... after having two 2GM20 engines over say 20 years, I have replaced one thermostat because it was faulty - stayed half open all the time. I currently have one Yanmar thermostat whose age is unknown but could be 30 or 40 years and still works.

I wonder if Yanmar called this up in the xQM20 & 30 engines as they were originally marketed as small commercial workboat engines without any gauges so there is no way to know if they failed in the fully open position (engine runs too cold). Purely speculation on my part .

[Compass790]

Originally Posted by Symphony

Does anyone replace their thermostat annually? that was mentioned in the manual snip kindly posted by Wotname: replace annually or every 2,000 hours.

I run about 150 hours annually.

CORRECTION: I should have said we've had the yacht for 3.5 years & dont know the thermostat age.

[hzz9g1]

Every year I do some preventive maintenance with the raw water system...


1. Check/replace the raw water pump impeller (check every 6mo, replace every year.)
2. Check/replace zincs (some newer engines don't have them)
3. Close loop the water system, attach a pump and run Barnacle Buster through the system for 5-10 hours to clean out the heat exchanger. You must remove your zincs before you do this. This has been one of the most valuable things that I have done to keep the engine running at normal temps throughout the season.

4. check the raw water filter for sticks and grass. Make sure it's clear.
5. Check the exhaust elbow..... if this gets clogged up it will create back pressure and your engine will also run hot. More than likely you'll also start running through a lot of impellers because they are over working to get water in your engine. Salt builds up in the elbow after some years... also rust. Probably not a bad idea to replace the elbow if it is cast iron with a newer made from a composite material if available.



If the engine isn't running warm,,, could be the thermostat is stuck open.



Doing this yearly maintenance ensures a happy engine

[Lnewman]

White smoke can be unburned fuel or steam. You can tell if unburned fuel by placing your hand into the smoke and then sniff (or taste).

I had white smoke with my 3GM30F. It was steam. In the end I found that the small elbow that connects the hose from the heat exchanger into the mixing elbow was almost totally clogged with crud. Seems to be a common problem. The crud was restricting the flow of water, so poor flow through the heat exchanger. I was getting water out the exhaust, but ends up not the correct amount of flow.

This elbox is a small half inch brass (or bronze) elbow screwed into the mixing elbow. I removed the hose, then brass elbow and scraped all the crud out with a screwdriver. Re-installed elbow and hose. No more white smoke. And way more water coming out the exhaust.