MD2020 High Exhaust Temperature

[Jokani]

First sail of the season at the weekend, happy days, well almost.

2 hours of motoring, a cracking sail, 1 hour of motoring to enter harbour and moor.

As it was the first time using this engine which has just had new pistons, valves, injector pump, raw water pump, new thermostat & exhaust elbow I kept a close eye on the Nasa Ex1 temperature guage/alarm.

All day it stayed between 35 & 37 degrees, perfect!

But after I moored up, engine still ticking over, the temperature had risen to almost 50 degrees. I checked that there was plenty of water coming out of the exhaust, there was. The engine overheating alarm did not go off, but the engine bay door was hotter than I expected, and there was an amount of coolant in the bilge. I switched off, and an hour later restarted, checked the strainer was clear, I have clear pipes so can see the water circulating, still plenty of exhaust water, but exhaust temp still rsing to high 40's. No other checks or temp measurements completed as started to dry out and had to come home for the weekend.

I do not understand, I have a new raw water pump, the water is circulating, how can the exhaust temperature rise if there is lots of water.

Any advice much appreciated.

 

[TSB240]

Our MD 2010 used to run all day flat out no alarms come into dock or moor up at tickover and it would actuallly trigger the temperature alarm and blow off a little water from the pressure cap. Water at exhaust was warm but not so hot that you could not keep your hand in it. (No in exhaust temp gauge fitted)
Impeller and cover plate in as new condition gave very good sea water flow..

Turned out to be a blockage in the freshwater circuit. In our case it was a blocked aluminium spigot on the exit from the exchanger/manifold block. Check heat exchanger and FW hoses for getting kinked or sludged up.

Antifreeze must be changed at least every two years to inhibit internal corrosion on FW side.

 

[Jokani]

Thanks TSB, the hoses are all new, the heat exchanger pipe has been cleaned, so I guess any blockage must be in the main block, or the water pump had failed.

I could replace the pump, just less than £100, and use something like Wynns Radiator flush to see if it would clear a blockage?

After flushing, other than firing up the engine and seeing if it overheats, is there a way to test if the coolant is circulating?

A real pain, as I will need to remove the thermostat which is a PITA on a MD2020.

 

[Jokani]

Hi TSB, just re-read your post, something I do not understand is, you ran the engine all day the water must have been circulating or it would have over heated, so unsure how it would over heat at the end of the day. Is it that when the engine is working harder there is more pressure forcing the water past any blockage, and when you tickover the pressure is reduced and the water stops circulating. Just trying to get my head around it. That being the case it would be a patial blockage that I flush might clear?

 

[cmedsailor]

Some time ago on my MD2030 I could see the sea water circulating but I was loosing the coolant. Eventually I found out that after removing the heat exchanger tube to clean it was not put back correctly and the coolant, via the rear black plastic cap, was finding its way through the exhaust. So check these two caps hold the tube exactly in place.

Edit: Probably doesn't answer your question but still a very simple thing to check....

 

[Trundlebug]

Gary,

I wouldn't worry too much about the temps you quote above.
For reference my temps are as follows (taken when fully warmed up after some crusing).
Running, exhaust temps around 30 deg C.
Running, engine bay ambient around 40 deg C
Idling, exh temps around 37 deg C
On start up after going through a lock - exh temps will match engine bay temp, which can rise to as high as 50 deg C because of heat soak. If only idling there isn't enough flow to cool it down sufficiently to bring it down to belwo about 40 deg, but as soon as I raise the revs above about 1,000rpm the exh temps will drop towards 30 again.

Just a case of getting to know what it does in normal conditions, so you recognise when there is something amiss. If your gauges are new and you're still getting to learn about what happens, don't assume there's anything wrong.

 

[TSB240]

Hi TSB, just re-read your post, something I do not understand is, you ran the engine all day the water must have been circulating or it would have over heated, so unsure how it would over heat at the end of the day. Is it that when the engine is working harder there is more pressure forcing the water past any blockage, and when you tickover the pressure is reduced and the water stops circulating. Just trying to get my head around it. That being the case it would be a patial blockage that I flush might clear?

You have got it!
At full revs the circulating pump developed sufficient pressure and flow through a pin hole sized blockage in the spigot. The flow and heat exchange to the seawater was sufficient to prevent over heat.

However on slow down the residual heat in the engine combined with the lower pressure and flow from the FW circulating pump was not enough to prevent overheat.

In our case the circulating water was blocked down to a 3mm Diam. restriction with calcium type deposit in the aluminium spigot. Once cleaned out it was nearer to 15mm Diam.

Steve

 

[lw395]

Gary,

I wouldn't worry too much about the temps you quote above.
For reference my temps are as follows (taken when fully warmed up after some crusing).
Running, exhaust temps around 30 deg C.
Running, engine bay ambient around 40 deg C
Idling, exh temps around 37 deg C
On start up after going through a lock - exh temps will match engine bay temp, which can rise to as high as 50 deg C because of heat soak. If only idling there isn't enough flow to cool it down sufficiently to bring it down to belwo about 40 deg, but as soon as I raise the revs above about 1,000rpm the exh temps will drop towards 30 again.

Just a case of getting to know what it does in normal conditions, so you recognise when there is something amiss. If your gauges are new and you're still getting to learn about what happens, don't assume there's anything wrong.

I would think the engine has built up some heat due to the hour's motoring.
I'd imagine the whole engine block side of the coolant circuit (not the seawater side) would be up above 70 degC.
The thermostat is working, the heat exchanger is regulating the temperature.
Bear in mind 'the temperature' is not uniform across the engine. Heat is moving from the cylinder head to the coolant. The inner bit of the head, must therefore be hotter than the coolant.
As the engine slows to tickover, the seawater flow slows. The heat is still initially coming out at the same rate. So the sea water gets hotter to remove the stored heat.
It's the same with a car or motorbike where the temperature gauge will often rise when you slow to a crawl in traffic. The airflow has slowed, the heat is still coming out from the head at the same rate. Sometimes the radiator fan will come on when the car has stopped. Cars will boil over when they hit a jam after 30 miles of fast motorway.
When you stop your boat engine, the temperature of the head, block, coolant and seawater stored in the heat exchanger will tend to even out. There's not much sea water stored, so it can easily get up near 'engine temperature'.


The lost coolant needs to be kept under observation. It may just be that the system was overfilled to start with? A lot of boats don't have a car-style catch bottle or expansion vessel, they rely on air space in the top of the heat exchanger. Any air trapped in e.g. calorifier circuit can expand and push out coolant. so it may sort itself out.
50 degree sea water is not a problem in this situation.

 

[Jokani]

Many, many thanks for the help and advice, really appreciated!

Yes, I believe I did top the coolant up to the top, I will put the pipe in a bottle, or see if I can find a suitable expansion tank.

There is nothing to say that the system had ever been flushed, so I'll do that just to be sure.

I'll fit a temperature gauge that I can see from the cockpit, so I can keep an eye on it, and I'll set the EX 1 to 50 degrees.

Thanks again.

 

[VicS]

Many, many thanks for the help and advice, really appreciated!

Yes, I believe I did top the coolant up to the top, I will put the pipe in a bottle, or see if I can find a suitable expansion tank.

There is nothing to say that the system had ever been flushed, so I'll do that just to be sure.

I'll fit a temperature gauge that I can see from the cockpit, so I can keep an eye on it, and I'll set the EX 1 to 50 degrees.

Thanks again.

You may well find that the coolant "will find its own level", below which it will not normally fall and at which level it will not expel any coolant. This may be lower than you expected but it will certainly keep on ejecting coolant if you keep on topping it up brim full

The exhaust temperature increase you are seeing does not seem to be excessive. At idle the raw water flow will be lower, even with everything in perfect working order, the mixing between with the exhaust case may not be as effective and the EX-1 may be giving a misleading indication. ....... the important thing will be how does the EX-1 reading compare with the actual temperature of the exhaust system well downstream of the elbow..

Why set the EX-1 as low as 50. you know its likely to rise to that. I'd set it few degrees higher. I believe the default setting is significantly higher

 

[Jokani]

Thanks Vic what you say makes perfect sense as usual.

At the moment I think it's set to 75 or 80 which is what it was for the MD2B it replaced. I do not want alarms going off distracting me when I am mooring, I'll set at 55 initially and increase if necessary.

 

[Trundlebug]

I haven't set my alarm yet, I have waited until I knew what the typical readings were for a few years.

However I have decided I'll be setting the alarm at 70 degrees.

Typically, highest seen temp I've seen, heatsoak, is maybe 52 degrees.
I know that the plastic in my silencers goes soft at about 90 degrees.
So I think 70 degrees is a good figure to give adequate margin between the two.
If it goes off, I know it's a real problem.