Our starboard engine has been running a touch cooler than the port, so we pulled the thermostats to check them.
Heating them up in a pan of water showed them starting to open at 160 degrees F and fully open by 175. This seems normal, but we replaced them with spares anyway. Engine temps are from our mechanical Murphy gauges, so the senders are not likely wrong.
After installing the new t-stats, the engine still runs a little cooler than its brother, 165F compared to 175F with sea water temperature about 60F at cruise RPM.
Impellers are new on the raw water pumps, heat exchangers are clean.
Suggestions are welcome.
Posted by Steve Dashew (October 16, 2012)
October 16th, 2012 at 4:27 am
Swap the gauges or take an independent measurement of both engines with the same instrument. You know what they say about assumptions!
October 16th, 2012 at 4:32 pm
I should point out that the variance is on the LOW side. We have never had an overheat problem. It is just that running a little cool is not optimum.
October 16th, 2012 at 6:09 am
Is there a way to swap the Murphy temp sending units to confirm they are working?
Don
October 16th, 2012 at 6:11 am
If it the problem isn’t on the cooling side, it must on the side generating the heat in the first place, meaning that one of the engines is operating less efficiently. Perhaps an issue with one of the injectors?
If so, one would expect to see a difference in fuel consumption between the pair – do you have a way of measuring that?
Also, is it an issue of one of them running cooler, or the other just a bit hotter to attain the same rpm?
October 16th, 2012 at 7:54 am
HI STEVE,
I PRESUME THE DEERE HAS A WATER CONDITIONER/FILTER WHICH IS CHANGED AS SERVICE INTERVALS. IF THESE ARE NOT ADHERED TO A SCALE BUILDUP IN THE WATER GALARIES IN C/HEAD & BLOCK WILL HAPPEN WHICH WOULD IMPEDE WATER FLOW. AND OR THERE MIGHT BE A SMALL OBSTRUCTION SOMEWHERE CAUSING THIS SMALL TEMP DIFFERENCE.
BEST
GRAHAM
October 16th, 2012 at 4:07 pm
Good idea. We’ll see about descaling. We do have good salt water flow, and have always used Deere coolant, undiluted.
October 16th, 2012 at 10:36 am
Steve,
Is the port prop fouled?
What are the relative exhaust temps prior to cooling water injection? This could indicate a leaner fuel/air ratio on the port engine.
Jeff
October 16th, 2012 at 4:08 pm
EGT typically is within a few degrees, usually one percent, using K type thermocouples on the N2K system.
October 16th, 2012 at 12:25 pm
Hi Steve. I came across this once. The water flow was the same in both engines but it turned out that the lube oil flow was restricted. Still had pressure but limited flow to the head. Just a thought.
Ken
October 16th, 2012 at 4:09 pm
Interesting idea. We’ll pursue this line of thinking. I assume there would be a temperature delta on the lube oil if this were the case?
October 16th, 2012 at 1:34 pm
The following is a Wild Amateur Guess, my knowledge of diesel engines is shallow and untempered by serious work. I’ve owned diesel vehicles and studied the acoustic signature of diesel engines for the purposes of imposing torpedoes on their operation, but I’m light years away from real experience as a mechanic. A relatively small obstruction in the cooling flow could cause a non-catastrophic variation like this. If you measure cooling fluid pressure on the input and outflow from the engine this might show a different level of pressure drop. Do the engines both use the same heat exchangers, and if so, can you swap them? If this is something new, and the heat exchangers use different raw water feeds, I’d look for plastic debris getting past the filters. I don’t know how amenable that system is to coat hanger clearance, but this may be a long afternoon of using naughty words while mucking with the plumbing.
October 16th, 2012 at 4:11 pm
Salt water side has good flow and temperature at injection elbows of the salt water shows identical temperature. So, the odds are it is on the fresh water side.
October 16th, 2012 at 1:39 pm
By the way, I’m going to take this as the final proof that not everything steamed goes well with hollandaise sauce. As always, if I’m wrong, please correct me. Your lady constantly impresses with her ability to accomplish marvels on a yacht, and she might well have a recipe for thermostats that makes them entirely palatable.
October 16th, 2012 at 2:05 pm
I would start by checking the accuracy of the Murphy gauges. If one was reading five degrees low and the other 5 degrees high that would be your ten degree difference.
October 16th, 2012 at 4:59 pm
Were the gauges (and/or) temperature pickups ever actually calibrated to a known standard? A 5 or 10 degree variance over the range of a mechanical temperature gauge isn’t that big, it could easily be within design tolerances for the gauges.
What does your IR thermometer show for the respective housings?
October 16th, 2012 at 9:51 pm
Both Murphy gauges and VDO electrical gauges show a similar trends. However, these are relatively inaccurate. On the other hand, the K-type theromouples wew have on the engines are very accurate,and positioned exactly the same.Bottom line, all three sources show similar results.
October 16th, 2012 at 7:59 pm
Do the electronic gauges mirror the Murphy gauges? I would also swap gauges first. If the swapped gauges show the same issue swapping the heat exchangers between engines makes sense.
The only original thought to this discussion I would add is that hoses between the engine and heat exchangers may be suspect. I have seen failure (partial) of oil lines to oil coolers that caused reduced oil flow to the cooler and an increase in oil temp. on an air cooled engine. I changed old oil cooler lines on Lehman 2715s and the water temp decreased a small but noticeable amount.
October 16th, 2012 at 9:52 pm
All hoses on both engines, both connection to the salt water feed, and the custom moldings, were replaced as part of the 6000 hour preventative maintenance cycle.
October 16th, 2012 at 8:00 pm
Just saw Ken’s comment. So much for original….
October 16th, 2012 at 10:11 pm
Hi Steve. Only the oil in one part of the motor was restricted so the heat buildup was localized and the oil temps were only slightly different but the cooling water was hotter.
October 17th, 2012 at 4:02 am
A few more thoughts Steve, might be an idea to pressure test the water system via your coolant tank. This will negate the obvious. Also try to check temperatures per cylinder as your Deere has wet sleeves and one might be in need of replacement.(because of rust and or o-ring breakdown causing restriction on coolant flow)
October 17th, 2012 at 2:11 pm
If I may ask a few clarifying questions. Did the starboard engine’s temperature drop or did the port engine’s temperature rise? When did this occur? What changes were made right before the temperature changed. Are you running the same coolant in both engines and are the same dilution ratios used.
October 17th, 2012 at 3:25 pm
Starboard has been cool for three years. Same coolant, have changed T-stats three years ago with no impact. No dilution – as it comes from Deere. No changes to the engines of which we are aware.
October 18th, 2012 at 2:06 pm
I am still trying to decide are we trying to explain why the starboard engine started running 10 degrees cooler or are we trying to explain why the port engine started running 10 degrees warmer.
October 18th, 2012 at 6:56 pm
The cooler engine is the question,and it not a recent occurance.
October 17th, 2012 at 2:49 pm
Steve,
I had a similar issue with my twin Yanmars. On the Yanmar heat exchangers the cooling water flows through half the heat exchanger tubes, reverses direction at the end cap and then flows back through the other half of the tubes and then exits. For some reason, small stiff straight organic fibers about twice the diameter of human hair couldn’t make the 180 deg flow reversal on the port heat exchanger and restricted the flow through the system just enough to make a 10 deg difference. This only on my port engine. The starboard engine did not have any of the fibers when it was inspected. It is a mystery as to why only one engine would pick these up and pass them through the strainers and raw water pump and not the other engine. Raw water intakes are separated by only about two feet. But that fixed it. I, like you, check multiple points on one engine against the other engine with my laser thermometer, which is what got me investigating in the first place.
October 17th, 2012 at 3:27 pm
Interesting, but in our case the temp issue is cooler, rather than hotter. Probably not a biog deal, but it has bothered me for a long time…
October 18th, 2012 at 6:37 am
As Daril says, first of all swap gauges, if difference remain, swap sensors.
I’m Telecom Eng. and never will forget what a professor on the university says, “the only electronics you can be sure will never fail is the one that don’t exist” Absolutely any device, being as good as you want is subject to failures. And if this is a matter of live or dead, make a redundant system.
October 18th, 2012 at 10:34 am
Just an idea: Do you have a water heater connected on one of the engines?
October 18th, 2012 at 11:33 am
Heat exchangers on both engine for domestic heat, however these are normally shut off.
October 18th, 2012 at 5:55 pm
How about using your non contact thermometer on various parts of the cooling system of both engines? See where the differences start to arise…
October 19th, 2012 at 11:27 am
Hi Steve, might be worth checking out both engines S/N & ask JD if there have been any modifications (on galleries etc). One of your blocks/cylinder-heads might be from a different batch to the other in this respect.
October 22nd, 2012 at 2:40 pm
Hi Steve,Please consider the variable accuracy of the K type thermocouples (2-4%) at full range. Apply Charles Law and convert to a 4-20ma output. You’re not likely to see a stable output without dampening the signal. I would recommend rescaling or at least verify the thermocouples match.
October 23rd, 2012 at 5:47 am
Hi Steve,
3 Years??? Long Time!!! What have you change at this time, and never change it since?
As engine temp are made from a conjunction of so many different factor, try reverse thinking:
What make the port engine temp rise 3 years ago???
Unless a broken thermostat, or broken thermostat seal, I have some really difficulties to believe that one engine temp can drop!
Have you take care about singing propeller 3 years ago???
Regards
Alain
October 23rd, 2012 at 7:52 pm
The three years, Alain, is a guess. But the props have been balanced to class S, thermostats replaced, and during this period the fuel injection pumps have been overhauled and fuel injectors replaced. The exhaust system has also been modified on both engines. So, we are left with a mystery. The slightly cooler running engine is not a problem, it is just a mystery.
Thanks to all the SetSailors who have sent in ideas. If we find the answer one of these days we’ll so advise!
October 24th, 2012 at 7:25 am
Steve, my apologies if I’m being obtuse, but on reading your original post and all the comments I return always to the same point (which some other people have also raised and you have not addressed): why do you characterise this situation as (a) the starboard engine as being cool, rather than as (b) the port engine being hot or as (c) there being a difference in temperature between the two engines? What I’m getting at is that there may not be a single explanation to be found in the starboard engine, but there may be one or more factors in the starboard and/or the port engines.
October 24th, 2012 at 2:06 pm
Good point, Justin:
The port engine temp runs in a normal range, so our feeling is the starboard is a little cooler.But not a big deal, just a mystery we’ve been unable to solve.
November 23rd, 2012 at 10:32 pm
Steve, I would strongly consider swapping the engines, side for side. Then run them in reverse. That is the only way…
Um… Actually I enjoyed this post and all the intelligent responses. And your (and others) undying curiosity and work to find this vexing issue. I was thinking maybe a casting passage issue, and scaling was suggested… then the aux heating tap, but you all have it covered. Short of a dyno to see how much heat/fuel was going in and out, im kinda tapped. This problem STARTED right? Not just born that way? EGT on individual ports, even non contact, just a relative reading between jugs has probably been done? This would reduce the chance of it being a valve/injector/fueling/cylinder balance type problem. OK, how about fresh coolant bypass? Could one be bypassing more water around the thermostat? Air Bleed or air pocket issue? How about the fresh water pump flow. If the clearances change between the impeller and the pump body, by rebuilding or wear, this can really affect pump flow. Ignorance might very well be bliss for some….
Nice job all. The internet gains a point.