mikuni heating problems

[Jacqmar]

Hi can anyone help please,

Our mikuni mx40 heating failed a few weeks ago and the warning lights suggested a new glow plug,sure enough the glowplug was burny out so we ordered a replacement.

Fitted this and heating was working and rads heated up.Left the boat for a week and when returned the heating was not working again.

[Jacqmar]

Hi

continuation of below!! oops!! pressed wrong button!!

the warning lights advised again glow plug problems so called Mikuni who advised probably needs de-coke. They can do this but the cost is c. £200 plus we will have to buy another glowplug!

Anyone know if it's possible to do the de-coke ourselves or is this a job for the experts?

Maybe it would be cheaper to get a heating engineer in?

Thanks

Martin

[Theo]

Hi

continuation of below!! oops!! pressed wrong button!!

the warning lights advised again glow plug problems so called Mikuni who advised probably needs de-coke. They can do this but the cost is c. £200 plus we will have to buy another glowplug!

Anyone know if it's possible to do the de-coke ourselves or is this a job for the experts?

Maybe it would be cheaper to get a heating engineer in?

Thanks

Martin

 

The glowplug is quite easy to take out but be careful with the insulating washers when you undo the wiring. Once it is out you will be able to see the fairly heavy guage wire heating element with the carbon sticking to it, mostly at the top. I use a wire bush to get rid of this but if that is not doing the trick it may well be possible to burn it off in a barbecue! (That's what I do with my Aga burner). Then refit it and see how you get on.

 

A new glowplug will cost you about £20 so it is a lot cheaper than the engineer. We keep a spare on the boat so that we can be cleaning one while using the other.

 

HTH

 

Nick

[DaveR]

The Mikuni is very voltage sensitive. Before I removed mine it was often the case that I had to start the engine to raise the voltage enough to ensure a start.

 

Sorry to be negative but on the Bensham (40 foot) there really wasn't a need for a central heating system. On red diesel I found that mine was more trouble than it was worth.

[Theo]

The Mikuni is very voltage sensitive. Before I removed mine it was often the case that I had to start the engine to raise the voltage enough to ensure a start.

 

Sorry to be negative but on the Bensham (40 foot) there really wasn't a need for a central heating system. On red diesel I found that mine was more trouble than it was worth.

 

 

Oh, NO!

 

I quite thought that I had merged the topics but on the computer that I am using at the moment most of the posts seem to have disappeared!

 

Sorry all :-(

 

Nick

[Tommo]

Hi can anyone help please,

Our mikuni mx40 heating failed a few weeks ago and the warning lights suggested a new glow plug,sure enough the glowplug was burny out so we ordered a replacement.

Fitted this and heating was working and rads heated up.Left the boat for a week and when returned the heating was not working again.

 

With the Mikuni it is absolutely vital that you clean out the boss, (that is the part that the glow plug screws into) there are tiny swirl holes in it that must be kept clean or the plug will carbon up in no time at all.

Take out the plug, turn off the fuel supply and disconnect the fuel pipe from the boss. Undo the 2 screws and pull out the boss from the unit, probably quite still due to the carbon. Make sure you don't lose the steel washer fitted round the boss. Clean off all the carbon from the wire gauze and carefully clean out the swirl holes with a small drill bit. Fit a new plug, you will also need a new gasket for the boss (Mikuni Part No 012058).

 

As for servicing the unit, it really depends on how hands on you are. I would say that if for instance you carry out engine maintenance then it should be well within your capability.

 

Ian

Edited March 29, 2007 by Tommo

[Theo]

With the Mikuni it is absolutely vital that you clean out the boss, (that is the part that the glow plug screws into) there are tiny swirl holes in it that must be kept clean or the plug will carbon up in no time at all.

Take out the plug, turn off the fuel supply and disconnect the fuel pipe from the boss. Undo the 2 screws and pull out the boss from the unit, probably quite still due to the carbon. Make sure you don't lose the steel washer fitted round the boss. Clean off all the carbon from the wire gauze and carefully clean out the swirl holes with a small drill bit. Fit a new plug, you will also need a new gasket for the boss (Mikuni Part No 012058).

 

As for servicing the unit, it really depends on how hands on you are. I would say that if for instance you carry out engine maintenance then it should be well within your capability.

 

Ian

 

What an incredibly useful reply, Ian. Thanks.

 

Nick

[Jacqmar]

Thanks for all your answers !

We will try your suggestion Ian. And Nick where do you get your glowplugs for £20?? The one we ordered from Nantwich chandlers was £39!

Thanks again

[GLYN FORSTER]

I had the same problem with a mikuni in one of my boats, i cleaned the glow plug boss as described by ian but it packed up again after a couple of weeks, i found it was contaminated fuel causing the problem, so i would reccomend checking your fuel to make sure you havent got water or the dreaded fuel bug in it, im not saying this is the definite cause just a suggestion..

 

The best place i found for parts was mikunis own shop the glow plugs are just over £20 and the glow plug boss is only £40 so maybe relace the boss instead of cleaning it, ive added a link to the website below.

 

http://www.mikuniheating.com/MX40mspare.asp

Edited March 30, 2007 by GLYN FORSTER

[Theo]

Thanks for all your answers !

We will try your suggestion Ian. And Nick where do you get your glowplugs for £20?? The one we ordered from Nantwich chandlers was £39!

Thanks again

 

 

I ordered mine direct from Mikuni. I hope that I am not misremembering the price.

 

Nick

[Jacqmar]

Thanks to all and our heating is now working!

Bought new glow plug and boss from Mikuni and will keep old boss for a spare.

Thanks again

Jackie

[Theo]

Thanks to all and our heating is now working!

Bought new glow plug and boss from Mikuni and will keep old boss for a spare.

Thanks again

Jackie

 

It just goes to show how very useful this forum is!

 

 

Nick

[Bird man]

Can anyone tell me how to test my mikuni mx40 fuel pump to see if it works. I'm not getting diesel through. Can I just put 12v dc over it to see it it ticks ?

[adrianh]

No, don't apply 12 volts directly to the pump as I think it is design to run of a lower voltage.

I think the operating voltage is about 9 volts and only short pulses at that.

Before you suspect a faulty pump rig up a guaranteed air tight feed pipe to suck fuel from a bottle preferably higher than the pump, then use the heater control box startup with the pump outlet open to see if it primes.

This pump is not supposed to be installed horizontally also..

Have you checked any fuel filters before the pump ( it should have 1) for blockage or diesel bug.

Only once in 25 years of running this pump have I had to replace the 3/16 inch od copper pipe from the tank to heater  after it became blocked with a wax deposit, this was caused by prolonged use of red heating fuel at the time.

Spares for this heater are almost impossible to find, pm me if you have other questions, I will help if I can

[Bird man]

Thanks so much for the reply.

I'm sure I have a pump problem as I cannot hear the loud clicking (I did and accept my hearing isn't the best). My partner says she can hear it, but it's not the loud clicking I had heard. I know the boiler will fire up as it has, but stopped. But now after a full strip down and clean up , it will not and I have one red light - ignition issue.

I tried with the copper hose off and no fuel pumped out.

Glow plug is working I can feel the heat.

Fuses all Ok.

Water pump and air pump work .

Have now cleaned the flame sensor.

Have checked the pump filter, nice and clean.

I did quickly try the pump with 12v quick faint click.

I have 2 spare MX40 so tried the other pumps also (before I read your advice 😐) one spat a bit of fuel out the other nothing.

Does polarity matter ?

I will try your test however - thank you.

Am thinking of getting a new 12v pump (I know it will not be the right one) see if that helps.

 

Any help gratefully received.

Many thanks.

 

[adrianh]

Good luck fixing this, are you sure that you have a free flow of fuel to the pump?

My experience a long time ago was that the pump does not self prime easily and that you need to have the internal plunger of the pump ' wet' for them to get pumping, so you may need to suck fuel through manually if you can

I do not think that any other pump will work as the amount pumped per pulse is critical to get the correct combustion parameters.

On start up the pump pulses quite frequently, so you should hear (or feel) that OK.

If you have spare control boxes then try another one, for a while I had firing problems but luckily was able to get hold of another controller to fix this.

Mine got quite damp and this upset the electronics!

[Bird man]

Many thanks. Will give it a try this weekend. Ps do you know if polarity on the 12v leads is critical ? I think I put them on the correct way but am doubting myself !

[adrianh]

If you mean the supply to the heater then I would think yes unless it has diodes in the controller to protect against this.

If you mean the pump then reversing the polarity probably will not damage it but may move the internal slug only slowly and possibly in the wrong  direction as the magnetic field will be wrong relative to the internal magnets.

Incorrect polarity feed to the fan and water pump would make them spin in reverse so I do not think the controller would allow this.

As I understand the controller all functions are monitored at startup, hence the ability to shutdown and display the various flashing light codes on the controller if things are not right.

You only need a corroded fuse in any of spade holders or poor power supply for this to happen, along with poor fuel feed, dirty flame gauze, almost burnt out glow plug and poor/blocked combustion air flow to trigger these errors.

Over the years I have found tired batteries to be the biggest cause of startup failure, along with the main supply fuse holder becoming heavily corroded. I now have a small bolted 20 amp fuse in the main supply and 6mm square size short wires directly from the battery isolator.

Since doing this update it is usually a dirty flame gauze that messes up ignition, luckily a fairly quick fix in situ sorts this.

The glow plug is readily available on line, details on the boat but available if you need info.

 

[bridge100]

Have you cleaned out the small thimble filter in the feed end of the pump The Brass cylinder unscrews

Mine was blocked and the pump would not work Cleaned it up and worked fine

[Bird man]

I have thanks. I also cleaned the large filter which it feeds from. I put it all back together again and it's fired up ok not smoking and getting  nice and hot.

After about 10 mins it closes down and does 9 flashes. Suggests not enough coolant in the system. The expansion tank level also increases too.

The rads don't bleed anything ! 

 

I need to change the towel rad. So my plans now is drain the system. Take off each rad in turn and flush through with hose and then reassemble and refill. See if that works. Also flush through the pipe work if possible. Suspect it's not been done for years.

 

So glad for the help I'm getting on the forum. Thank you all.

I feel I'm getting there bit by bit. 

 

[adrianh]

Make sure that after flushing you refill with premixed anti freeze and distilled water.

Mix your own as you will need a maximum of 25% antifreeze.

If the mix is too strong it does not conduct heat away from the burner quick enough ( as your fault) and the small circulation pump cannot cope with the higher viscosity.

After a flush/refill I got all this wrong and had to start again to get the system running!

[Bird man]

Many thanks 👍 

[Bird man]

To all who helped and advised me on sorting Mikuni out. So far, so good. I now have heat and hot water. Am really chuffed.

Thanks everyone if ever we meet up I owe you a 🍺