Engine Operating Temperature

D

dclagett

Well-known member
Joined
Aug 9, 2016
Messages
498
Fluid Motion Model
C-26
I am looking for other Volvo Penta D3 owners experiences with their engine operating temperature. I have a RT 25SC with a D3 150 engine and I operate the boat on the Chesapeake Bay.

When I first purchased the boat at the end of August last year my operating temperature was about 187 degrees cruising at 2700 rpm. At the time the impeller had just been replaced and the hull bottom was clean. This temperature was consistent at the 2700 rpm until I hauled the boat in mid November. When the boat was hauled there was minimal growth on the bottom, mostly on the trim tabs and some on the prop. Also, during this time period the bay water temperature had cooled considerably while the operating temperature stayed the same.

This year when the boat was put back into service at the end of April the operating temperature was about 187 degrees. I did not change the impeller, based on past experience with other boats. The bottom was completely cleaned and repainted with Micron CSC and all metals were painted with Pettit Barnacle Barrier. Over the last 3 months since the boat has been in the water the operating temperature at 2700 rpm cruise has climbed slowly until now it is running 198 degrees. We have had a very hot summer and the bay water temperature has increased to about 84 degrees. The engine operating temperature does reduce immediately when the rpms are reduces and returns to about 177 degrees at idle (same as last year). Also the boat has been operated almost every week and over the 3 month period I have put about 45 hours on the engine.

Over the last 3 months the bottom accumulates some slime sitting in the marina which washes off when running. The trim tabs have accumulated a coating of algae, looks like hair, and does not wash off with running. The engine raw water strainer has been completely clean during this period and the raw water wash down, which uses the same sea strainer, seems to have the same water pressure/flow. So it seems that the engine should be getting the same amount of raw water, if the impeller is OK. I have not noticed any vibration when operating so I assume the prop has not accumulated any growth.

I have been told by several folks that this climb in operating temperature is normal based on the bay water temperature increasing. I guess I am not sure this is correct. Before I change the impeller or haul the boat I would like to know if others have had a similar experience and did they find a problem or find that this is normal.

Thanks in advance for your response.
 
Our 2015 R25SC operates at 178 degrees at all throttle settings up to about 2600 where it climbs to 185 or so. Fresh water lakes.
 
tlkenyon":1uqlphfa said:
Our 2015 R25SC operates at 178 degrees at all throttle settings up to about 2600 where it climbs to 185 or so. Fresh water lakes.
Click to expand...
Those are the numbers with our 2017 with 75 hours. Didn't change over the winter but then water temperature doesn't change much. We spent 20 years in the Chesapeake and can relate to that slimy goop you are boating in right now.
 
I would like to hear from someone that operates in water temperatures that change 25 to 30 degrees over the season.

Thanks
 
At the beginning of our season, the water is at 50 or so. Right now, the water is approaching 80. Water temp does not have much to do with the normal operating temps, as the thermostat in the engine controls the temp. At the higher op temps when approaching WOT, the thermostat is wide open and cooler water temps might have some influence.

TK
 
TK,

Thanks, I would agree with your assessment as long as sufficient water flow is available. I can't find it now but there is a reference to thru-hull size for sea strainer on this site. Apparently at one point the thru-hull was sized by Fluid Motion for the cooler waters of the West Coast. It took a larger size thru-hull to support operation on the East Coast. You have the temperature differential I was looking for, what year is you Tug?
 
My Classic R21 is 2005. My R25sc is 2015. We use the little tug "Little Nellie" on the lake where we live, and the 25 "Big Nellie" on larger lakes in the area. We are leaving in about 5 weeks for the loop...with Big Nellie, of course. 🙂

TK
 
Thanks for your reply. My Tug is a 2014 so I assume if it is a restriction problem with the water flow it would not be the thru-hull size. I found some another references on this site to restricted water flow in thru-hulls where marine growth inside the thru-hull has caused engine temperature problems. The way they solved the problem was with a dowel to clean out the thru-hull from inside the boat. I think I will try that first, before I go to other costly measures. I don't think is is a scaling issue inside the heat exchanger since the boat has only been in service 2.5 years. If that doesn't work I will try the reverse gear heat exchanger flush, but I don't think that is a problem since the sea strainer has always been clean.

TK, have a great time on the loop. Are you going to do it in segments or are you going to go for the entire loop until complete? Either way safe travels.

Richard
 
From my unfortunate experience, impeller failure can be gradual, wherein it keeps up with the heat load of low RPMs but cannot keep up with the heat load of high(er) RPMs. Add to that the possibility of a partially lost impeller vane in the heat exchanger. In the absence of any other clear cause, you might consider an impeller change....something I have been dreading. The impeller in the Classic 21 is EASY by comparison, only tool required being a screwdriver.

We are doing the loop in one shot (or at least plan to). Starting in mid-Illinois and heading south. You can follow us on Nelliemay.com.

TK
 
The impeller is on my list of things to try if needed. I was thinking that it should be OK since it was changed 1 year ago. I viewed the movie put out by RT and have changed impellers on my larger boat years ago, however in trying to get the cover plates off to just take a look at any access issues I found that someone has stripped the heads of the screws holding the covers in place. Fixing the screws was on my list of things to do this week. Power screw drivers are good if used correctly.

I look forward to following your adventure. Thanks for sharing the site. My wife and I love boating but don't think we could stay on our 25 long enough to do the entire loop.

Richard
 
...guess we are gonna find out just how long a year really is.....

TK
 
If you have a clear strainer you should be able to tell if the inlet is fouled. The strainer should be completely liquid full at running speed. If you can see air in the strainer when running then the inlet is restricted. Maybe just the algae that you described causing a restriction.
 
Dan,

That is a good point. I do have air at the top of the strainer. The air has been there since it was launched this season. Not having the boat that long I am still learning. I think I will spend the $$ and do a short haul this week. I can't remember if there is a strainer on the water intake on the outside of the hull. If so maybe in painting the metals the yard applied to much paint to the slots restricting the water flow. I was not able to inspect the work before the boat was launched.

Thanks

Richard
 
I'll throw this out there, but I (and others) have had problems with the belt tensioner sticking or freezing from corrosion on my D3-150. This condition might be allowing some belt slippage on the water pump at higher rpm. I encountered the issue on my 2013 25se on the first impeller change. Just a thought...
 
Check your reverse gear heat exchanger. This symptom is indicative that you have some build up of debris in there. Just because your strainer looks clean does not mean that small particles did not get through and clogged the reverse gear heat exchanger. If I were a betting man this is the first place I would address.
 
I was also going to change the impeller this week, so I will find out it the tensioner is ok or not.

Thanks
 
The reverse gear is on my list of items to look at. That is easy to do, maybe I will do this first. Dan does have me concerned about the air in the seawater strainer, if he is correct then I have an issue with the water intake.

Thanks
 
I think there are 2 main reasons for the increase in temperature on your volvo D3 assuming your strainer is clear (the most obvious reason)

1) Disconnect the hoses on either side of the intercooler and backflush with a hose and pick out all the weeds and debris that can slip through the strainer, but still get caught in the intercooler. This is where the raw water connects to the engine. Someone posted a nice picture of how to do this in the past but I can't find it now. To back flush spray from starboard toward port side. I was surprised to see how much small seaweed and sea grass was trapped there.

2) The small section of hosing on the starboard side of the intercooler can collapse under high speed if it has softened or cannot get enough flow due to restriction from above. Mine seemed to collapse after 3000 RPM's and temp would go up to the 195 or higher range (even after I cleaned the intercooler weed out). After replacing this section of hose (on my 2014 R27), the new hose doesn't collapse at higher RPM's and no more problems with temperature! Hope this helps.
 
I want to thank everyone for their comments and advice on my engine temperature rise and follow up on the solution to my problem. I tried a couple easy items such as backflushing the reverse gear heat exchanger and checking the tensioner for the raw water pump belt, no problems found with either item. I did not change the raw water pump impeller since it only had 75 hours on it and it had never been run dry.

I had a diver checkout and clean the metals today and he found that the external raw water strainer was almost completely blocked by barnacles. In addition the diver was quite surprised on the small size of that strainer. I was surprised that the raw water strainer had barnacles since the metals I could see (trim tab, rudder) did not have barnacles just some algae and all metals were painted with the same antifouling paint.

So the engine is now back to running at 187 degrees at 2700 rpm in 84 degree water.

This winter I may increase the size of the external raw water strainer to help extend the time between dives.

Thanks again for all your help.

Richard
 
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