Temperature overheat alarm not working on Volvo Penta MD2020

[Sinbadtong]

Good evening,
A few weeks ago the sound alarm on my Volvo penta MD2020 went off whilst motoring. However, the temp warning light did not come on, and engine appeared fine. Nevertheless, returned home just to be safe. Next day checked normal overheating causes, including impeller etc and no obvious causes, and engine still running fine, apart from very irritating alarm! So - short term measure, disconnected alarm and have been sailing and motoring with no problems for last 3 weeks. However, I now need to get it sorted, don't really want the alarm disabled..... I've done a little research, I'm wondering if it is the temperature sensor that needs replacing, but my question is that if it is a faulty sensor, would the temperature warning light not also be illuminated? Why is it just the audible alarm sounding incorrectly? Any suggestions gratefully received. Many thanks

 

[ylop]

Obvious questions (which probably means you have checked these):
- have you checked the bulb is working?
- how did you determine it was overheat not oil/alternator alarm?
- after the first incident when you test does the alarm come on instantly when you start the engine or only once it’s been running for a period?

The temp sensor is just a switch that closes - and connects the wire to ground (when the warning light and buzzer should then work). It’s easy enough to remove the sensor wire and see if it stops the problem. Which if the engine is cold at the time would suggest a faulty sensor/switch (but the light should come on too).

 

[TSB240]

Welcome to the VP control panel annoying alarm club.

I had a similar problem with ours with exactly the same symptoms..

I did all the usual voltage and current checks to ensure all the connections , switches and alternator were fine.

Eventually I had to bite the bullet and replace the entire light and control module.
It is a potted module with diodes that can break down given a small amount of moisture ingress along the cables.

I borrowed a working one from a good friends boat to check if mine was fried.

Second hand ones are like gold dust.

New ones are now supplied with leds not dull indicator lamps.

I think I purchased mine from ASAP. Not cheap but sailing time without nagging alarms is worth the investment!

If you look on other posts about these problems you may find a wiring diagram of the potted control unit. This may help you identify if you do have a duff diode.

You are on a fools errand if you think you will ever replace an individual diode. They are encased in a potted circuit board that I virtually destroyed before getting anywhere near repairing it!

 

[TSB240]

Sorry it wasn't ASAP.
It was Keypart.
Logic Control Unit for Alarm Module - Genuine.

 

[Sinbadtong]

Obvious questions (which probably means you have checked these):
- have you checked the bulb is working?
- how did you determine it was overheat not oil/alternator alarm?
- after the first incident when you test does the alarm come on instantly when you start the engine or only once it’s been running for a period?

The temp sensor is just a switch that closes - and connects the wire to ground (when the warning light and buzzer should then work). It’s easy enough to remove the sensor wire and see if it stops the problem. Which if the engine is cold at the time would suggest a faulty sensor/switch (but the light should come on too).

Morning, thanks for your reply. No problem with obvious questions - this is my first boat / engine so I'm sure there are many things I'm not aware of....

Yes - bulb is working.
I wasn't aware it was the same alarm for oil / alternator.... however, a few weeks previously I did have an overheat problem - not enough coolant after winterization - but quickly sorted and engine been fine since - however that may have caused the problem with the sensor?? I'm assuming not oil / alternator as no issues with either of these - batteries charging and oil level constant

Yes - alarm comes on as soon as I turn ignition on when engine is cold.

Will try reconnecting alarm and disconnecting sensor wire - but as you say warning light should be coming on with alarm but is not - so wonder if it's wiring to alarm rather than the sensor?

 

[PabloPicasso]

Sorry it wasn't ASAP.
It was Keypart.
Logic Control Unit for Alarm Module - Genuine.

I nearly spat out my coffee when I saw the price of that . It just a circiut board module, not even the complete panel

Its either made of gold, or more likely, part of Mr Volvo's pension plan

 

[Sinbadtong]

Welcome to the VP control panel annoying alarm club.

I had a similar problem with ours with exactly the same symptoms..

I did all the usual voltage and current checks to ensure all the connections , switches and alternator were fine.

Eventually I had to bite the bullet and replace the entire light and control module.
It is a potted module with diodes that can break down given a small amount of moisture ingress along the cables.

I borrowed a working one from a good friends boat to check if mine was fried.

Second hand ones are like gold dust.

New ones are now supplied with leds not dull indicator lamps.

I think I purchased mine from ASAP. Not cheap but sailing time without nagging alarms is worth the investment!

If you look on other posts about these problems you may find a wiring diagram of the potted control unit. This may help you identify if you do have a duff diode.

You are on a fools errand if you think you will ever replace an individual diode. They are encased in a potted circuit board that I virtually destroyed before getting anywhere near repairing it!

Thanks for the welcome - although not sure it's a club I want to be a part of!

I'm hoping I don't need to replace the light and control module! I'll do other checks first -but if this is the issue thank you for signposting me to the answer, and saving me a lot of time!

 

[TSB240]

A cheaper and better temperature alarm for any wet exhaust is this one.

Shop
This won't eliminate your annoying alarm but it will give you confidence that your not going to melt your muffler and fill your boat with water and exhaust gases!

 

[TSB240]

I nearly spat out my coffee when I saw the price of that . It just a circiut board module, not even the complete panel

Its either made of gold, or more likely, part of Mr Volvo's pension plan

My Scottish ancestors rolled in their grave after shelling out for it..


OEMs typically will have a minimum of 400% mark up on spares. The stockist will also add their profit margin.

I tried to repair mine but it just requires too much time and effort to gain access to a few cheap diodes.

On the bright side you do get new leds that replace the old bulbs that are virtually impossible to replace when the holders are badly corroded.

 

[Daydream believer]

My alarm used to go off on my MD2020 & I found that by disconnecting some of the plugs & re connecting them it solved the problem. Although my boat is a pretty dry boat I think that a bit of damp still affected the connections . So disconnecting & re connecting solved the issue. I do recall spraying some electrical contact cleaner on them as well

 

[Sinbadtong]

My alarm used to go off on my MD2020 & I found that by disconnecting some of the plugs & re connecting them it solved the problem. Although my boat is a pretty dry boat I think that a bit of damp still affected the connections . So disconnecting & re connecting solved the issue. I do recall spraying some electrical contact cleaner on them as well

Thank you - will try that - certainly sounds cheaper than a new module!!!

 

[Sinbadtong]

So I managed to get to the boat and investigate a bit more today...
The wiring diagram and engine drawing say there should be a white and brown wire leading to the temperature switch (relay) and a light brown wire leading to the sensor. The white and brown wire is obvious and leads to the switch - see photo. When I disconnected it the alarm buzzer still sounds, so that's not the issue. However, it seems there is no sensor - at least, not where the manual says it should be on the side of the engine just behind the alternator. The wiring diagram says it is a light brown wire. I could see a light brown wire, but this is crimped off in a white block - again see photos, and it seems that where the sensor should be is just a blanking plate/bolt?

So this suggests that the sensor must be somewhere else? Does that sound right, and if so - where is it likely to be - exhaust?

If anyone can confirm or correct my analysis so far, and suggest where to look next for the sensor I would be very grateful. Many thanks

 

[ylop]

@Sinbadtong - I could be wrong here, but I suspect the “sensor” is an optional extra - unless you have a gauge showing engine temp (which you’ve not mentioned so far) I doubt you have it. The “relay” you have found is probably essentially a temperature switch. When it gets above a set temperature it closes and connects the wire to the body of the engine which of course is grounded, and in so doing completes the circuit. The question is does the alarm stop when you disconnect that wire?

 

[Sinbadtong]

Ok, that's interesting...
There is no guage.
Yhe alarm doesn't switch off when I disconnext that wire....

 

[Ammonite]

The blanking plug behind the alternator is for the optional temperature "sensor" for a seperate gauge. You can also get an optional oil pressure sensor - a small metal canister about the size of a cotton reel, which sits at the forward end of the rocker cover if fitted. These are number 19 in the schematic below.
MD2020-C Electrical System - marine diesel engines

The water temp "switch" is number 17. Don't confuse it with the oil pressure "switch" which is number 16

As ylop says these are just switches that operate when the set temperature (95c) is reached, or pressure (about 5 psi) in the case of the oil pressure switch

 

[Sinbadtong]

Thanks, so that confirms that I dont have the optional temp sensor, just the relay switch. The issue now is that disconnecting that relay doesn't stop the alarm sounding, so presumably that's not the fault, and if there is no temp sensor, where is the fault???

 

[TSB240]

https://forums.ybw.com/attachments/vp-electronic-module-jpg.98791/

I think you know the answer.

It is one of the diodes in here.
It can't be anywhere else!

You can't test which one without destroying the module.

I think your membership of the annoying alarm club is fully confirmed.

 

[Sinbadtong]

 

[chriss999]

It might be worth ditching the alarm altogether and looking into the cost of a temperature sensor and separate temperature meter. My predecessor installed a VDO temperature sensor and meter into my engine so I can see the temperature from the cockpit.
Admittedly mine is a Beta not a Volvo, but the principle may be similar. A cursory google search suggests that they might be cheaper than the £300+ option above.

As an alarm I have an exhaust temperature meter. Mine is by Silicon Marine but Nasa also do them.

 

[philwebb]

I wonder if you could gain access to the circuit board by dissolving the potting compound. I’ve got a 2010 and the parts look the same.
The potting compound is probably silicone, in which case Screwfix 88987 might remove it. If the part is £400 it could be worth a try.
Diodes are easy to test and cost pennies.