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Would an engine operating at 100 deg at cruise give any cause for concern?

 

Diesel engine, old, pressurised coolant system to heat exchanger, sea water cooled. No other obvious problems. Oil pressure drops as the engine heats up, assuming this is the oil getting less viscous.

 

This is occurring at cruise revs, no where near max revs. Can't decide if it's a problem or perfectly normal for a pressurised system.

 

We motored out to Tiri with the kids last weekend, don't normally run the engine for long enough to get so hot, (normally motor out and put the sails up) so don't know if this is a new problem or not.

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what are you measuring?

 

oil, water, radiant surface heat off the block?

 

what are you measuring with?

 

cheap gauge, expensive gauge, external meter?

 

closed loop "fresh" cooling water should be about 110C, 90C, which is why you have a pressure cap on a radiator...to keep it under pressure and not boiling 

 

raw pump through salt water would be much less  

 

oil should be over 100C, so air vapour that gets into the engine oil through combustion gets boiled out.....which is why you should never just run your engine for 6min on + off the mooring......you need about 30min of running occasionally to boil all that condensed water out

 

probably your system is fine

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if it has a pressurised system 

 

next time it's hot make sure it's pressurising by using a rag and quickly 1/4 turning the cap off and back on

 

pressurised hot water should pulse out if under pressure

 

ideally your gage should climb to 100 85C after about 10?min of running

 

and maybe climb a little higher after 30min....

 

oil pressure will always drop a bit as viscosity drops with heat

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Sorry, measuring coolant near top of the head, in the same spot as the thermostat.

The sender and gauge aren't old (i.e have been replaced at some stage, the engine is circa 30 years old). Wouldn't say they are calibrated, but believe them to be adequately accurate.

 

Temp usually sits at 90 degs as we cruise off the mooring and out of the river being 15 min at low revs (as as not to speed in the mooring area). However, after motoring for a bit, the gauge has had a habit of jumping rapidly from 90 to 100 and back again, and occasionally up to 105. This initially gave me the shits, so I throttle back to avoid any risk of engine damage. One school of thought is this is actually the thermostat opening and closing as the coolant reaches operating temp. The gauge is in the same piece of manifold as the thermostat.

 

The owner has been wondering if we have had a loose earth wire making the sender temp jump round. i.e. temp change has been appearing random and intermittent.

 

This last weekend, motoring out the gauge was jumping around (unstable temp) between 90 and 100, but coming back was steady on 100 the whole way, regardless of revs. Both trips were circa  1hr 30 min of steady running.

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hmm...

 

research rather than memory

 

seems to suggest 90C is about normal operating temp, at idle?

 

but up to about 110C is ok if engine is working hard

 

http://mechanics.stackexchange.com/questions/1340/my-cars-coolant-temperature-reaches-almost-100-c-212-f-in-a-fast-pace

 

as well as anti-freeze and corrosion inhibitor, glycol coolants also raise the boiling point to about 120C 

 

The PCM commands Low Speed Fans ON under the following conditions: Engine coolant temperature(ECT) exceeds approximately 106°C 

 

 

What I been told is, the perfect working temperature for a diesel engine is 90ºC, thats why all brands diesel engine work at that temperature.

Not all of them. I think 90ºC is a tad hot, though certainly not detrimental. One can swap out thermostats to open at a cooler temp. My Dodge runs a steady 82ºC and runs just fine. :v 

You can push a diesel to run hotter than 100ºC...put a real load on it when its hot outside

 

does the engine have an overheat sensor and light?

 

up to 120C shouldn't be too much of a worry but jumping around sounds a little odd

 

if it is an old engine

 

when was the last time the heat exchanger core was taken out and cleaned?

 

if it's the brass type made of small tubes they do eventually clog up if not cleaned yearly and lose effectiveness

 

but that wouldn't cause fluctuations......

 

dodgy thermostat might? 

 

it'll cost a new gasket but they can be tested by removing and slowly heating in water to see what temp they open

 

often stamped on to them 80C, 85C, 87C etc

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The cooling system is designed to run at normally 83 deg c. That's what's on the thermostat as well, for most engines. It should NEVER get hotter than thermostat fully open temp. 100 is too high. Confirm temp at thermostat housing with IR thermometer (cheap on trade me, and worthwhile tool for your boat). If the 100 is right, and the impeller is ok, it will get worse, as above it's probably the heat exchanger being fouled. Run it flat out for a few mins - does the temp go up more? If so, impeller, thermostat, or fouled heat exchanger are the likely causes. I wrote a bit about cleaning heat exchangers on another thread a while ago - I'll find the link.

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Sorry, measuring coolant near top of the head, in the same spot as the thermostat.

The sender and gauge aren't old (i.e have been replaced at some stage, the engine is circa 30 years old). Wouldn't say they are calibrated, but believe them to be adequately accurate.

 

Temp usually sits at 90 degs as we cruise off the mooring and out of the river being 15 min at low revs (as as not to speed in the mooring area). However, after motoring for a bit, the gauge has had a habit of jumping rapidly from 90 to 100 and back again, and occasionally up to 105. This initially gave me the shits, so I throttle back to avoid any risk of engine damage. One school of thought is this is actually the thermostat opening and closing as the coolant reaches operating temp. The gauge is in the same piece of manifold as the thermostat.

 

The owner has been wondering if we have had a loose earth wire making the sender temp jump round. i.e. temp change has been appearing random and intermittent.

 

This last weekend, motoring out the gauge was jumping around (unstable temp) between 90 and 100, but coming back was steady on 100 the whole way, regardless of revs. Both trips were circa  1hr 30 min of steady running.

Thermostats do die,I suggest you change that as well as all the other checks that are talked about here.
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Yep as IT said.
The very fist thing to check is rubber impeller on Raw water cooling pump and if it is an old pump, check the pump body is not too worn.
After that, Thermostat. I would not even bother with testing it, simply replace it. They are cheap. A sure sign they are not working properly is the sudden temp changes. A Thermostat should work fairly smoothly. They don't "switch" open, they open slowly as temp rises. You will see a point where the gauge sits reading cold then rises fairly fast, but it should not be a sudden jump.
Temp gauges are not accurate to the degree, but within a few is fine.
Operating temps of engines vary slightly, but Marine Engines normally work in the low to mid 80's. Not like a Vehicle engine where there is a huge amount of cooling available via a Radiator and they can afford to run at higher temps. Yes higher temps make the engine more efficient, but there is a lot of air around the engine in a Vehicle. 40% of the cooling is done buy the Oil. A Boat does not have that luxury of cooling air and the larger engines need heat exchangers on the Oil as well.
Back to subject, also as IT said, Heat exchanger is third on the list.
Also, how long ago since you drained the Coolant and put in fresh? Often the coolant becomes damn near a soup of rusty old water. Coolant has a limited lifetime as a corrosion inhibitor. Which is VERY IMPORTANT. The cheaper coolants need to be replaced annually. Better ones are around two yrs. There are some new ones on the market now that have service times of 7 and 10yrs. A good coolant does several things. Anti corrosion, Anti Cavitation corrosion, and a wetting agent that creates a better water to metal surface contact to aid getting the heat away from the engine walls.

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Thanks for the info, sounds like I've got some work to do.

We do check coolant regularly but haven't changed it in a while. Raw water pump was recently re built. Heat exchanger has been given a full birthday, but prob 10 years ago now.

 

I'll start with thermostat and move on from there.

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Supplementary question, I've been mucking around with the prop, increased diameter and have been adjusting the pitch (Kiwiprops) initially we were miles off max revs, now we are close to being within 10% of max revs, but have a reasonable cruise speed.

 

Would changing the engine's 'work' cause or contribute to this high running temp?

We were a long way from max revs when it was running at 100 deg. Cruise is approx 1,800 rpm giving 6 knots (hull speed around 7.5 knts or so). We are getting about 2,500 rpm max with the current prop set up, while designed max revs is 2,800 rpm. Max torque is around the 1,800 to 2,000 rpm range.

Engine was not labouring or doing black smoke, was running sweetly other than the temp issue

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How embarrassing, while poking around in the engine instruction book for details of the thermostat (to replace it), I found this little gem

"The cooling water temperature is normal if the thermometer indicator falls with 70 to 85 deg."

So I clearly have a problem. With the engine that is and not my ability to read a manual. That info is in the pre start checks section, not any of the technical sections.

 

Also turns out, under the fault finding section is that everything you have all said is applicable, including overloading.

I don't think it's overloading due to my prop tinkering, I'm going with dodgy thermostat and carrying on from there until I clean the heat exchanger.

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The prop will effect the loading on the engine at revs where its not producing max power, if overpropped. Normally a labouring engine will produce back smoke. The engine should have plenty of cooling capacity if in good order, and you should NEVER be ABLE TO OVERHEAT it regardless of what you do, 70 deg seems cold to me , are you sure thats not for a raw water cooled version?

In my experience, thermostat is possible but less likely than a problem heat exchanger, but easier to check, so do that 1st :-) Take it out, if you want to test it, put it in a pot and boil it. It should start to open near its rated temp, and open smoothly, without catching and then moving more quickly. Same when it cools and closes. Most of them are pretty low cost - except for some modern engines where you ahve to change the whole housing!

 

You should  prop the boat to actually acheive max revs, then run it at about 80% of that for cruising. This ensures proper loading and will give best economy.

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depending on the type of heat exchanger core

 

they like to be removed every year or 2 

 

cleaned, (pipe cleaner down each tube) greased? and put back in with new coolant

 

coolant that is so old it has changed from green to skanky khaki 

 

can mean they've been allowed to weld themselves in....

 

1325664--002.jpg

 

making them very very hard to clean without damaging

 

don't ask me how...

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Yes load on the prop will cause over heating. What IT said about the engine being able to keep ool at all speeds/loads is correct, except the older engines sometimes did have cooling issues under heavy loads. for instance, if you read the post I made about my boat having a speed problem which turned out to be the prop severely fouled, the engine temp would rocket up through 100 deg and the alarm would go off is i tried to puch the revs over 1400RPM and all I could get was 4kts and into a head wind, down to 2 kts and then in a head on Gale, no headway at all. After the prop was cleaned, I could push the engine to full RPM and just over 8kts and no over heating. Remember that Raw water volume is also subject to RPM. Low RPM and not enough cold water for an engine working hard.

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Phosphoric acid at a 4 or 5 (water) to 1 (acid) concentration will take care of any build up in the HE tubes, it will not damage them. It "can" be done in situe, as long as you can raise the inlet and outlet hoses above the HE. carefully pour the mixture into one end, it will bubble as it re-acts with the lime deposits, hence the slow pour to stop it overflowing while working. Once the bubbling has stopped (10 minutes or less ) its work is done,. re-adjust hoses to allow the HE to drain into a container so you can dispose of the solution in a correct manner. Re-connect and run engine, any residue (minimal) will be diluted and flushed out.

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Thanks for that Steve, that information is really handy for where we are at with it just now.

The owner has taken the heat exchanger off previously and reckons it is a fairly major job. It is integrated with inlet manifold. Last time he did it he ended up having to re-tap some studs, so I am interested in having a go at cleaning it in-situ. We are fairly sure we can take the ends off to inspected the element. If we can then clean it with phosphoric acid in situ, with the judicious use of hoses, then that will simplify the job considerably.

 

Is phosphoric acid easy to get hold of?

 

For our jumping temp gauge issue, our maintenance records show we have moderately recently (couple of years ago) changed the temp sender unit and the gauge. On discussion with the supplier, the most likely cause of our jumping issue is a dodgy earth connection apparently, followed closely by a stuffed thermostat.

 

So hopefully my hot engine issue is actually an instrumentation problem and not a hot problem. We do have an over temp alarm, that has not gone off yet. Regardless, I'm still keen to at least inspect the heat exchanger, and if I can clean it in place, will do so.

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I replaced my dodgy thermostat before christmas, it cost $60something at Repco. I then heard about hi flow thermostats as used in performance cars, and bought one of those to fit or carry as a spare. It cost $40 something at Segedins on Dominion rd.

Its best to pull the old one and take it along with a vernier or ruler. . some are simple single action things , some ( like mine ) are diverter types and work in a duplex kind of way.

Get the multi fit gasket kit while you're there.( or better , take the neck along too.)

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