Onan MKDAV (7kw diesel genset) problems...

[Cymen]

I recently purchased a 2003 Privilege 465 EC which came with a Onan 7kw genset (MKDAV). This genset worked without issue for a week or two but one day I noticed a very strong sweet smell that seemed to come from within the hulls not outside (so not via the exhaust). I assumed this was a coolant smell of some type so cleaned and topped off the coolant overflow to the C/cold line. The hose was plugged up a bit and the coolant in the overflow a bit rusty but not oily.

Then began the odd experience of having the generator continue to work fine however any coolant in the overflow tank always disappeared. I couldn't find it in the bilge and whenever the coolant level was checked by removing the pressure cap (on the machine, I'd call it a radiator cap normally but it's not on a radiator) everything was good.

So I kept on running the machine until yesterday at about 1 hour and 20 minutes run time the generator stumbled, black smoke was emitted and the circuit breaker tripped. I waited for the machine to cool and find the coolant again at the normal level. I reset the circuit breaker and then tried to use the generator. It starts without issue and runs just fine until we try to switch our onboard power source to the genset. Then it dies immediately. The switch blinks 3 times to indicate "service required" and, per the service manual, I pressed the STOP side of the starter/control button and then we received a more detailed error code of 27 or "loss of voltage sense".

So that is where I am now -- per the service manual, I should do this:

LOSS OF VOLTAGE SENSE—CODE NO. 27 (Controller unable to sense output voltage)

Corrective Action: (Refer to Page A-1 and to Page A-2 or A-3, as appropriate.)

1. Disconnect connector P3 (green) from controller A1 (Page 4-1) and check continuity between Pin 11 and S1 and between Pin 12 and S2. If open, check for missing, bent or corroded pins and faulty wiring and repair as necessary.

2. Test and service the generator (Page 5-2) as necessary.

3. Replace controller A1 (Page 4-1).

I'm struggling with step 1 in that I can't seem to find S1 and S2. The cover from the generator top indicates that Q1 and Q2 are the same as S1 and S2 however that hasn't helped in finding them. I will of course keep looking however I decided to post here in the hope that someone else might have some insight into this!

This is the service manual I am referring to:

https://www.seapowermarine.com/seapo...ice-Manual.pdf

[Cymen]

I finally realized that there are basically 3 parts to this generator (as setup for us):

1) generator itself
2) a separate box with what I think is the ac sensing mechanism and unsure what else
3) remote control panel (gauges, start/stop button)

I discovered #2 has some burnt connections and the plastic heating/melting/near burning (some is black) may be the sweet smell we had -- it looks like we narrowly avoided a fire.

Now to find the manual for that box or maybe it's supposed to be simple enough that it is covered in the main manual I just missed it.

[Cymen]

Although I'm not sure about any of this as the boat itself has the switch to determine power source and the sensing mechanism in the box may be for that part of the system (for it to indicate generator is sending power) not the genset.

Part of the problem is that a aftermarket heater was installed in the same area in a way which makes access very difficult. So removing that or at least getting it out of the way is the next thing to do.

[skipperpete]

Hmmm, it sounds like 2 different problems. If you haven’t had an automatic shutdown then either you didn’t have a critical engine event OR the auto shutdown circuit isn’t working. An overheat would initiate several responses and a shutdown ( low coolant sensor : high temp sensor: high temp switch and raw water flow) but you had none of these so if I was the guy getting paid to fix this genset, my first move would be to test the auto shutdown circuit, if that circuit is fully functional then I’d run the genset …off the board first then on the board with all loads isolated. Then I’d probably put a known load on for a while (electric kettle) and gradually …..one at a time with a long pause between each bring each of the other loads online while closely monitoring all of the engine vital signs…… temps, oil pressure, raw water flow and rpm (frequency). Usually if one of the isolated loads is brought back online there’ll be an immediate response from the generator if its the faulty or problematic load.
There is a vague possibility that this is an old problem that someone treated by defeating the shutdown circuit and I’d certainly be looking for signs of that at the senders.

[Cymen]

I think it is two problems. The coolant problem distracted from the big problem as I correlated the sweet smell of coolant with the smell we were observing. It turns out the smell was the plastic for some terminal connectors melting in a box. Likely due to some screwdown terminals being loose causing increased resistance. We have some very charred parts in the box that is for switching 220v AC sources (generator, shore, inverter). Thankfully, we avoided a fire but I suspect we came very close. After having someone remove the charred bits and connecting the wires directly (with soldering and heat shrink tubing along with replacing some of the short runs of wire that were damaged), we're back in operation.

So it all makes sense -- the Onan shut down due to loss of AC sense almost certainly due to a short circuit upstream (in the box mentioned above). So nothing was changed on the generator and it came back without issue after the fix.

I'll keep going on the coolant loss issue. Next up on that is replacing the tubing from the overflow to the engine as it is suspect. I'd also like to replace the radiator cap but I hesitate to throw parts at it (especially given the huge markup in parts cost where we are currently located). So I'll try to figure it out instead of playing parts roulette.

Unrelated but there is excessive corrosion at the diesel fuel line connectors (in and out) at the bottom of the Onan which I should also come up with a plan for. And a lesser concern but another thing to address is the severely rusting tray the generator sits in (it would be awesome if Onan made generators using stainless steel but I guess that would drive the price way up).

[GordMay]

Here’s the Onan ‘MDKAV’ (Spec A−C) Marine Generator Service Manual
➥ https://www.seapowermarine.com/seapo...ice-Manual.pdf

[Cymen]

So my problem turned out to not be the generator at all. The wiring/control box for switching from generator, shore, inverter and auxiliary overheated. Thankfully, we didn't have a fire. The cause was likely a loose screw down on some of the wires perhaps added by corrosion. After this issue was resolved, the generator came back online without issue. So almost certainly there was a short of some sort that indeed prevented detecting alternating current.

I haven't figured out the mysterious coolant issue but next step on that is replacing the overflow coolant tubes and making sure the overflow container doesn't have any leaks.