VP D1-20 overheating only at idle

[DeepFrz]

I'm thinking maybe the ramp in the water pump">raw water pump. They are often (always?) replaceable.

[MBWhite]

Originally Posted by rabbi

Today I did some motoring and sailing so had time for testing.
The engine did an hour at 2300 without issues. Temperatures quite similar compared to the other engine. The temperatures at entry and exit point of the heat exchanger was 94 celsius and 78 celsius, so the thermostat was open and the heat excbanger working. Head temperature measured beside the injectors was 95 celsius.
Wind picked up so i did an few hours of sailing and started the engine later to run at 1600rpm for motorsailing. After 20min the overheat alarm sounded and I stopped the engine.
Heat exchanger temperature was 78celsius entry and 75 celsius exit, below the thermostat threshold so the thermostat was closed. The head temperature was 110 celsius...
I started the engine 5 minutes later to run at 2300 rpm and temps went back to normal.
I don't see how blocked cooling pipes could possibly allow the temp to drop at high rpms.

I will test the coolant pump throughput tomorrow but i guess the pump is toast.
The engine block is perkins based so i hope to find a perkins pump for less than the volvo penta cost.

Rabbi,

I am a little confused with what you are describing, but I cannot complain and only apologize because your English is most certainly better than my German!

However, please do not be bothered but I wish to see if I am understanding your situation. Your heat exchanger will have 4 water ports, correct? There is an inlet and outlet for the "raw water" and also an inlet and outlet for the "engine coolant", is this correct?

The engine coolant temperature you measured at 94C going IN to the heat exchanger, and 78C coming OUT of the exchanger and going back into the engine.

When the engine overheated, you measured the engine coolant temperature at 78C going IN to the heat exchanger and 75C coming OUT of the heat exchanger, and at the same time you measured the Cylinder Head temperature to be 110C, correct?

During any of these measurements, did you take the temperature of the raw water going in and out of the exchanger? I am a little baffled by this, as your first measurement with the engine behaving there was a 16C drop, but when it overheated there was only a 3C drop. Since I would guess the raw water was 20C or so I would suspect that drop to be greater. A lot of interesting confusion happening here!

Anyway, what I would do at this point is NOT go and just replace the coolant pump just yet. It very well may be the problem, I had a similar issue once when the pressed-on impeller started slipping on the shaft, so it would overheat at times and then behave normally but while that would fit yuour scenario let us not condemn the pump immediately and rush out to buy another. You are fortunate that you have an identical; engine onboard which gives you the priceless opportunity to be able to switch parts between engines until the problem part causes the other engine to overheat instead.

So what I would do first is switch the thermostats between the two engines. Yes I know you have already replaced it with a new one but I have seen too many brand new items be defective to not rule that out. Anyway, you can swap the thermostats and when the problem still happens with the same engine you now have a great story to tell everyone about what idiots Americans are!

So after you replace the thermostat and the problem is still there, the next thing to do is remove the coolant pump and inspect it. If the impeller turns on the shaft then you have found the problem, but if it looks normal then go and swap it with the other engine and see which engine still has the problem. You can also compare the pumps against each other to see if one is more worn or damaged somehow.

Anyway, I would suggest to try that and post your results. I do not wish to be the bearer of bad news and suggest the problem is caused by a bad head gasket, so let us check the simple and cheap things first!

Regards,

MBW

[GILow]

This one is a ripper hey?

OK, my theory goes like this....

The coolant pump is stuffed, and is either freewheeling on the shaft slightly or the fins are damaged to the point where at low speed they are not pushing the fresh cooling water around the engine.

Therefore, they are not pushing the hot water to the thermostat housing (most thermostats have a small bypass hole to ensure the hot water gets to them so this is normally not a problem) so the thermostat is not opening and therefore the hot water is not being pushed to the heat exchanger, hence the lower measured temperatures of the water at the heat exchanger.

Now my theory gets a little weak at this point because the slow moving cooling water should have cooled down a lot more in the heat exchanger than normal, due to the slower cooling water movement, but then I regain a little bit of faith from the observation that rate of heat transfer is directly proportional to the temperature difference, so maybe the lower overall temp of the water in the heat exchanger is lowering the rate of heat transfer.

Yeah, ok, that last bit is a bit wobbly, unless the raw water coming into the heat exchanger is quite warm... but it's a start.

This is a good puzzle. Sorry for the OP, but it is interesting, and the OP is making some very good analysis, even if I can't make sense of it.

I look forward to hearing the solution to the problem.

Matt

[GILow]

Originally Posted by GILow

Now my theory gets a little weak at this point because the slow moving cooling water should have cooled down a lot more in the heat exchanger than normal, due to the slower cooling water movement, but then I regain a little bit of faith from the observation that rate of heat transfer is directly proportional to the temperature difference, so maybe the lower overall temp of the water in the heat exchanger is lowering the rate of heat transfer.

So thinking about it some more, it occured to me that the temperatures being observed on the heat exchanger may simply have been "leftover" hot water in the system from when there was adequate water flow. In a warm to hot engine compartment, where the engine had been running properly at full temp for some time, the fresh cooling water ceasing to flow through the heat exchange may well have remained hot in the pipes leading to and from the heat exchanger. Particularly possible if these observations were being made with an IR gun.

I've now completely convinced myself it is the fresh water pump, so I am going to be shattered when it turns out to be something entirely different.

Matt

[Snowpetrel]

I wonder if you can get a vapor lock due to the slowing water circulation on a hot engine, as you idle
down. Blocked vent lines, or no hole in the thermostat? Loose pressure cap or the wrong one could cause boiling? As could the wrong coolant ratios.

Just a completely uninformed thought, very interested in what you find out, good luck.

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[rabbi]

Originally Posted by MBWhite

However, please do not be bothered but I wish to see if I am understanding your situation. Your heat exchanger will have 4 water ports, correct? There is an inlet and outlet for the "raw water" and also an inlet and outlet for the "engine coolant", is this correct?

correct!

Originally Posted by MBWhite

The engine coolant temperature you measured at 94C going IN to the heat exchanger, and 78C coming OUT of the exchanger and going back into the engine.

Correct, thats the temperature of the metal housing of the heat exchanger where the coolant enters at 94C and exits at 78C.

Originally Posted by MBWhite

When the engine overheated, you measured the engine coolant temperature at 78C going IN to the heat exchanger and 75C coming OUT of the heat exchanger, and at the same time you measured the Cylinder Head temperature to be 110C, correct?

Correct

Originally Posted by MBWhite

During any of these measurements, did you take the temperature of the raw water going in and out of the exchanger? I am a little baffled by this, as your first measurement with the engine behaving there was a 16C drop, but when it overheated there was only a 3C drop. Since I would guess the raw water was 20C or so I would suspect that drop to be greater. A lot of interesting confusion happening here!

with the coolant at 78 and 75 degrees the thermostat was closed (it only starts to open at 90 degrees). So there was not much heat exchange happening and the small delta makes sense. Even with the thermostat closed there is still a little exchange going on through the metal housing.
The delta of the raw water was 14C while cruising (thermostat open) but only 3C when overheating (thermostat closed).

Originally Posted by MBWhite

Anyway, what I would do at this point is NOT go and just replace the coolant pump just yet. It very well may be the problem, I had a similar issue once when the pressed-on impeller started slipping on the shaft, so it would overheat at times and then behave normally but while that would fit yuour scenario let us not condemn the pump immediately and rush out to buy another. You are fortunate that you have an identical; engine onboard which gives you the priceless opportunity to be able to switch parts between engines until the problem part causes the other engine to overheat instead.

My problem with switching parts on old engines are worn gaskets and o-rings with no spares at hand. My termostat already started leaking.

Originally Posted by MBWhite

So what I would do first is switch the thermostats between the two engines. Yes I know you have already replaced it with a new one but I have seen too many brand new items be defective to not rule that out. Anyway, you can swap the thermostats and when the problem still happens with the same engine you now have a great story to tell everyone about what idiots Americans are!

The thermostat behaves correctly. I already switched them and of course now one of them is leaking. But both work the same way.

Originally Posted by MBWhite

So after you replace the thermostat and the problem is still there, the next thing to do is remove the coolant pump and inspect it. If the impeller turns on the shaft then you have found the problem, but if it looks normal then go and swap it with the other engine and see which engine still has the problem. You can also compare the pumps against each other to see if one is more worn or damaged somehow.

After my findings today i guess i can skip this, see below.


As promised i did a few pump tests today.
I rigged some clear hose where the coolant exits the heat exchanger and stuffed a wood plug into the return line that normally goes from that point to the coolant pump. That way coolant is drawn from the expansion tank and pumped through the engine and heat exchanger into the clear hose.
Holding the other end of this clear hose into the air i measured the static pressure of the coolant pump at different rpms. The higher the coolant rises in this hose the higher the pressure. Not very professional but good enough.

The faulty engine provides enough pressure to lift the coolant just 15cm or 6inches above the heat exchanger at idle, 65 cm at 1500rpm and 92cm at 2500rpm.
The good engine gives 25cm at idle and 120cm at 1500rpm. The hose was too short to measure at 2500rpm.

I also measured throughput by taking the time required to fill a 1.5 liter bottle from the coolant hose.
The faulty engine required 65secs @idle, 35ses @1500rpm and 24secs @2500rpm.
The good engine required 32secs @ idle and 24secs @1500 rpm. No measure point for 2500pm because dinner was ready

Based on these figures the faulty engine has roughly half the pressure and throughput at idle compared to the good one.

I guess GILow is right and the coolant pump is damaged. A partially blocked coolant pipe would influence the throughput but not the static pressure.
So taking out the coolant pump is the next step

We currently have family guests onboard and i don't want to pull the coolant pump right now to be possiby left with only one engine. The faulty engine is working OK at high revs so i just need to be careful while anchoring.
Early next week i will pull the pump and see what i can do.

What i already learned is that the coolant pump currently fitted is not the one normally used by Perkins for that engine. So i guess if its impossible to repair i will have to swallow the cost of a new Volvo Penta pump.

Thanks for all the ideas you shared so far. I will post the findings next week after i pulled the pump. If you have other ideas, please let me know!

[DeepFrz]

Nice bit of troubleshooting. Thanks for posting that. I look forward to what you find out about the pump.

[MBWhite]

Before the USA shipped all of our manufacturing and industry to China, there were shops that specialized in pump repair. You would drop off the faulty pump and pick it up the next day. You might enquire if they have such shops around where you are.

[GILow]

Originally Posted by rabbi

As promised i did a few pump tests today.
....

Rabbi, next time I have an engine problem I am contacting you to ask you to design the test regime.

On other matters, you mention that the pump used for the application is different to that usually used by Perkins. If you cannot get the current pump repaired, you might consider adapting the installation to the more readily obtainable pumps.

I recently went through something like this when rejuvinating our cooling system. I set out to remove all of the awkward, old, specialised bits of cooling pipe that were no longer obtainable, and replace them with very common pipes readily obtained from a local auto parts store. (So, being an Australian boat, I now have late 90's Ford Falcon cooling hoses, a very common car in Oz.) I just pulled the old hoses off the engine, took them down to the big auto spares chain near home, apologised to the staff in advance before sitting down on the floor in the aisle and pulling out all the hoses to find a better setup.

Now I know that if I blow a hose somewhere odd in Australia, I will be able to get whichever hose I need easily. (Though of course I carry spares.)

A bit of work, but if it works it would save you enough money, I suspect, to be able to afford to carry a spare pump (or two), which is much better way of spending money I think.

Good luck, look forward to hearing the results of the fix.

Matt

P.S. I hope dinner was worth stopping work for.

[GILow]

Originally Posted by rabbi

The higher the coolant rises in this hose the higher the pressure. Not very professional but good enough.

Really, not very professsional? Just "good enough"?

Mate, you are under-selling yourself, that was brilliant. A scientific test method using a freely available controlled variable (atmospheric pressure) as the reference point, all cobbled together on a boat, in time for dinner.

Brilliant.

Matt

[rabbi]

We are currently in greece in the small islands around Corfu. Greece means finding a good mechanic equals finding a huge diamond.
Getting spares or things like a pump repair shop will require roundtrips to Athens or Thessaloniki, the only two larger cities but 400km away.
I guess its faster to order the parts in Germany and have them sent to me via DHL.

The coolant pump is not the one that i found on the Perkins website and there are no specs available so hard to guess why volvo penta changed it. I don't think they did this without reasons, because keeping the standard pump would have been cheaper and easier for them.
So if its impossible to repair i will just swallow the cost.

I will let you know how things continue. Thanks for all the help and encouragement!

[olaf hart]

Great work Rabbi, but I am not sure you have excluded a partial blockage on the fresh water side of the heat exchanger.

May be worth a look before you pull the coolant pump. It's a very unlikely item to fail.

As an old teacher used to say, "common things occur commonly".

Perhaps you could repeat the measurements at the inlet end of the fresh water side of the heat exchanger?

[GILow]

Originally Posted by olaf hart

Great work Rabbi, but I am not sure you have excluded a partial blockage on the fresh water side of the heat exchanger.

May be worth a look before you pull the coolant pump. It's a very unlikely item to fail.

As an old teacher used to say, "common things occur commonly".

Perhaps you could repeat the measurements at the inlet end of the fresh water side of the heat exchanger?

I would expect that the static pressure method devised would be an adequate test to eliminate partial blockage, since partial blockage would only restrict flow, or would restrict pressure only when there was significant flow.

On the other hand, it is very good advice to check the simple stuff first, not least of which the input side of the heat exchanger may well contain the remains of the cooling pump fins.

Matt

[rabbi]

Good advise to check the simple stuff first. I already pulled the heat exchanger to clean it but there was nothing to cleanat the raw water side.
based on the heatexchanger design a block at the coolant side of the exchanger is unlikely.
Seawater runs through a set of pretty thin pipes which reside in the coolant,so there is very little chance the coolant side can be blocked.
But depending on the state of the coolant pump it will be interesting to see if there must be any debris and where it is now.

I am not completely ruling out a partial blockage but based on the static pressure test the pump has issues.

The figures also indicate there is no significant blockage:
The faulty engine required 24s to pump 1.5 liter at 2500rpms while the good one required 24s at 120cm (but at only 1500rpm). Same output with less static pressure indicates there is no blockage in the faulty engine.
Or at least the blockage is not worse than in the other engine.

[Snowpetrel]

The benefits of having two identical engines! Nice idea, and it makes me think I should measure/get more baseline data for my engine, since I only have the one onboard.

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