Engine overcooling - and undercooling

[gunnarsilins]

I had this question mailed once before, with no good response, so I´ll give it another try.
My sailing yacht is powered with an Perkins 4.236 diesel, 24 years old with nearly 3000 hours on the clock. The engine is fresh water cooled from the factory. Starts and works perfectly apart from some cooling problems.
When running at cruising speed, appr. 1700 rpm, the temperature gauge shows a little above 90 degrees – perfectly normal.
When going faster or slower temperature changes in proportion to the rpm´s. 2200 rpm = 105 degrees and when idling around 70 degrees.

I have dismantled the entire cooling system, both heat exchangers, exhaust manifold, all tubing, everything. Throughfully cleaned tubestacks and everything else. Checked the thermostate, and put a new one in, just to be sure. The raw water side is dismantled and cleaned as well and the flow is normal.
The only non-original item in the cooling system is a calorifier plugged in to the system.

Anyone got an idea? How can an engine overcool – and undercool at the same time if it´s not the thermostate???
All suggestions appreciated.

 

[ccscott49]

Is the gauge an electric one? I mwould tempoarily fit an old type capilary tube type temperature gauge and try it. If the gauge is capilary then you have me baffled, but I will thin k on it. If the capilary gauge shows nothing wrong, you may have a problem with the (sometimes fitted) volatge stabilizer, fitted either on the back of the gauge or somewhere in the instument panel, let me know. The fact that the gauge goes up with revs, points to voltage instability.

 

[david_bagshaw]

Over cooling

On our Sabres, which have a very high grade thermostat a similar thing happened at tickover.

Was told by sabre that the amount of air passing through the engine was sufficient to cool the block... due to the engines relatively low compression ratio, am sure you are experiancing the same.

Happens with Scania too.

David
www.yachtman.co.uk

 

[gunnarsilins]

Gauge fault/voltage variations

Yes, the gauge is electric. But I have checked it by getting printed resistance vs. temperature curves from VDO, I measured it at room temperature and when kept immersed in boiling water. Both values were accurate. So I hardly believe the sender is faulty. Besides, the yacht have two steering positions with the gauges doubled, they show similar values.

Regarding the voltage stability, no, there is no stabilizer fitted to the engine instruments. But, having two-coil gauges, shouldn´t the gauges give proper values regardless of voltage variations?
And if your theory would be correct, shouldn´t I get the same rpm-proportional readings on the engine- and gearbox oil pressure gauges? Yes, the engine oil pressure drops when idling with a hot engine, but stays othervise on 3,5 bar in the whole range between 1000 rpm and max. The hydraulic gearbox stays stuck on 10 bar, reads this regardless of temperatue and rpm, as it should.

On top of that, I have a digital voltage meter with two decimals which can be switched between the engine electrical circuit and the domestic one. This voltage meter actually got its source from the actual + feed to engine instruments when measuring this circuit. When idling there is of course a lower voltage reading in the system, but as soon the revs are more than 1000 rpm the voltage is very stable.

To mee this indicates that this is not a problem with inaccurate readings but it manifests from the engine itself.

Pleas enlighten me if I haven´t foreseen something!

 

[ccscott49]

Re: Gauge fault/voltage variations

Well, it seems I wasted your time, sorry!

 

[boatone]

Re: Gauge fault/voltage variations

When you change revs does the temperature gauge show the increase or decrease in temperature more or less immediately or does it take some time (comensurate with the time it would take for the actual temperature to change) ?
In other words, is the indicated temperature moving in sympathy with the throttle?

TonyR
boatone@boatsontheweb.com

 

[billskip]

OK you have checked all the technic stuff..and now down to the sillybilly thinking..thats my dept..has this just started to hapen??..if not posible that the water pump is not orig.and delivers to much water at lowrevs and not enough at hi revs..silly but?..

 

[billskip]

Re: Ge variations..cc

Only cos you beat me to it cc ..cos of my stutter..so I sent another instead....

 

[gunnarsilins]

Dear Colin!

You have definetely NOT wasted my time! No, I really appreciate you taking YOUR time and contribute with some very good points.
Gratefully yours!

 

[gunnarsilins]

David!

You might have a point here, especially when I have a calorifier plumbed into the circuit. This I believe takes its water "before" the thermostat and thus might act somewhat like an "extra" cooler.
But, what do you mean by a "very high grade thermostat"?

But your explanation does not explain the rise in temperature when running on high revs. Of course we might have two different faults here.
Overpitched prop? Well, I got what Moody´s once fitted her with.
Undersized coolingsystem? This I doubt, I live in Stockholm, Sweden and use the yacht all year round as long there is no ice, in seawater temperatures between close to 0 and well over +20 degrees. If the system were undersized, shouldn´t the rise in temperature decrease when the water is very cold?

 

[gunnarsilins]

Boatone and Billskip!

To my knowledge the waterpump seems to be original. I doubt it ever has been removed.

The temperature variations does not follow the throttle. I got a very slow rise, from tickover (70) to max revs (100+) takes about 5 - 10 minutes, the fall, the other way round is quicker, but still a couple of minutes.

 

[Chris_Robb]

Re: Tempearure variation!

I also have a rather ancient 4236, I do experiance a small rise in temp when running under extra load, but the tempearture does not drop below normal on idle.

I have a 12 gallon calofier connected, but is connected after the thermostat. This mede no difference to the running temps when I installed it.

My water pump is young, and pumps a massive amount of water. Perhaps what you are seeing is a cruising temp above normal, a fast running well above normal, and an idle at the correct temp. and this may be due to a slugish pump.

Visual inspection of the pump casing, - if you can feel any lip on the face plate for example, will mean that you are loosing a lot of pressure.

Sorry - not very useful other than to confirm that I do not get such a difference

 

[gunnarsilins]

Chris Robb!

Which water pump are you talking about? When you mention a lip on the face plate I get the impression you mean the raw water one. On this I have no lip, and I use the yacht in water temperatures varying between almost 0 degrees and well above + 20 degrees. I believe such difference in seawater temperature should affect the symptoms if the raw water flow was insufficient.

And isn´t a cruising temp of 70 degrees a little bit low? The thermostat has 85 stamped on it.

 

[scottie]

try to take calorifier out of the circuit
there should be cocks to isolate the calorifier if not think about fitting them

 

[Twister_Ken]

Re: Chris Robb!

The faster the engine goes the faster the pump turns and the more water gets pushed through the system. Is it possible the raw water pump and piping is not totally efficient, and a normal revs there is a sufficient but not generous flow of raw water, while at full revs, the inefficiency (like a small air leak?) gets overwhelmed and substantailly more water flows, causing increased cooling?

That's a stab in the dark from a non-engineer, but it does seem to fit the low-high-low symptoms.

 

[Chris_Robb]

Re: Chris Robb!

Yes - Raw water pump. Yes you would expect a slightly higher temp on Idle, mine is around 85.

The sea temp would certainly effect the fast running temperature, so if it does not, - it can't be that!

Another point - is the temp variation consisitant with a clean bottom? A fouled bottom will cause a much greater load.

 

[Twister_Ken]

Longer shot

At low revs the wave pattern of the boat leaves the raw water intake fully underwater. As the engine and the boat speeds up so the wave pattern changes, partially exposing the intake. At full chat the wave pattern has again submerged the inlet? Consequently, there is not full water flow at crusing revs.

Unlikely, but I have sailed a boat (Jeanneau 362) where the intake spent more time sucking air than water on one tack.

 

[david_bagshaw]

Re: David!

you say
I have a calorifier plumbed into the circuit. This I believe takes its water "before" the thermostat and thus might act somewhat like an "extra" cooler....

It would do as the engine warms but imagine the engine has been running for a while & the calorifier is full of water at 95 deg ,, when you slow to a tickover there will be a flow of heat INTO the engine from the calorifier as the engine is now at 70


you say
But your explanation does not explain the rise in temperature when running on high revs....&..If the system were undersized, shouldn´t the rise in temperature decrease when the water is very cold?....

What if the size of the thermostat hole when fully open is under size, even if the cooling water is cold, & the pump creating the correct flow, if the thermostat will not open further then the temp will rise. Experiment may be by removing the stat , & running, but not if of the type where as one bit opens it also closed another hole or flow way
You say
Overpitched prop? Well, I got what Moody´s once fitted her with....

If full rpm is reached now & is the same as before this is not the problem, and I agree with you is unlikley to be the cause.


My only other thought is perhaps the water pump is not putting out the correct flow at higher rpm, due to as others have suggested air leaks or general performance deterioation


you say....
But, what do you mean by a "very high grade thermostat"?....

An external industrial type see picture of the engine front , the thermostat is halfway up on the right for those unfimilar with the layout of sabre engines, at http://homepage.dtn.ntl.com/david.bagshaw/specials/engine_front1032.jpg


Hope that helps



David
www.yachtman.co.uk

<P ID="edit"><FONT SIZE=-1>Edited by david_bagshaw on Mon Dec 3 14:24:06 2001 (server time).</FONT></P>

 

[billskip]

Re: Chris Robb!

just re read your original question thought you said crusin wos 90 not 70 ..i no im dyslexic ..but i try..

 

[charles_reed]

The symptoms all point to a sticking thermostat.


If this is a relatively recent phenomenon - it may be the new thermostat.


You could try running with it removed for a period which should cure your overheating problem.

If it doesn't you've probably got one cylinder leaking into the cooling jacket pressurising the indirect cooling system.