Low engine temperatures

knotflying

Well-known member
Joined
Jul 25, 2010
Messages
6,014
Fluid Motion Model
C-28
Hull Identification Number
FMLT2731J011
Non-Fluid Motion Model
25' Parker & 246 Robalo Cayman
Vessel Name
http://illusionsmikeandjess.blogspot.com
I think I have figured out the issue, but figured I would put a post here for input. My normal temperature range is between 194 to 204. Currently at about 2500 rpm I am only getting 135 degrees and at WOT 200 degrees. I did use a laser thermometer at the engine and the block temperature is close to the Yanmar readings. Today while I am running I am going to check the temperature of the hot water from the head sink water. I am making the assumption that since the engine water circulates and heats this water the temperature should be close to the engine temperature. I will then compare this to the Yanmar display. My assumption at this point is it is a stuck engine thermostat and not a sensor or electrical issue.
I am told a defective thermostat is rare. Anyone had a similar issue?
 
Mike, I agree that the thermostat is the most likely cause. I would change it as a means of testing - yup, I are an expert technician, I change parts until the problem goes away (or the customer runs out of money).
I can't visualize at the moment where it is on your engine - hopefully it is more accessible than the raw water pump :roll:
 
Our Volvo runs between 174 and 200 degrees depending on rpms. I wonder if the water temps your running in has any effect on engine temps? Not in Mike's situation but as a general question.
 
I had a thermostat stick open in a 1963 4wd Willy's Wagon once back in the 70's. Found a new thermostat in rural N. GA, but had to use a ball peen hammer to tap out a new gasket that would work.

I'm curious, how many hours on your engine?
 
934 hours on the engine. I am told that the t-stat rarely fails. I never one the lottery, but won the one in a million t-stat.

I don't think outside water temperature, unless really drastic, should have an influence on the engine water temperature. Remember, it is a closed system and the t-stat opens and closes based on the closed system water temperature. If the ambient water is so cold then the t-stat should stay closed. If the ambient water is warm the t-stat would open. the t-stat opens full at 205 degrees. Therefore the ambient water would have to be fairly hot to not be able to cool down the closed system water.
 
Hi Mike, the engine temp on Gratitude has never gone above 197. At 2200-2800 RPMs we see 193-194 and at 3200-3300 we see 195 and those numbers are in the summer down here in FL. I've never run it at 4000 RPM's for more than a minute or two so I don't know how high the temp would go. I saw 197 once before I changed the impeller. Good luck with the thermostat change. Please post after you do it.

Tim
Gratitude
 
Update:
The new Thermostat is installed. WHAT A JOB! It took 10 hours for two men. I have not gone on the water with the boat yet to see if there is a difference in temperature. It is not possible to get the temperatures high enough on the trailer without a load and higher RPM's. The old thermostat was functional, but seemed to be dislodged from the seat. I am hoping all this work was not in vain, but I am suspecting it may be the sensor.
The other interesting thing is that between production years Yanmar changed the location of the thermostat. The manual shows it installed in a housing just above and slightly port of the seawater pump. On my engine you follow the outlet hose (larger hose starboard side) on that housing and it was located inside the housing that the outlet hose connects to. This is located underneath the heat exchange forward of the fill cap. The full procedure will require a book so if any other poor soul has to do this PM me and then we can talk on the phone. Make sure you have a nice big mirror, about 6" X 6" before you start.
I want to Thank Brian B of Gansett Ranger for his assistance. I could not have done it without his assistance and encouragement along the way. Also, Peter of Winter Island Yachts was a godsend in being able to tell me where the alternate location might be.
 
As much as we love our Tugs and as customer friendly the factory is, esp. Andy and Ron, it is time for the factory to step up and address these impossible to service issues. There is just no way to excuse this.
I would like to see the factory design and install after production access hatches to make access to the engine for all service items possible. And of course make those changes to the molds and production line.
 
Agreed, simple tasks should not require a major "pre-job" to get to "the job". However, we have small boats with big boat systems so we have to expect some inconvenience with service, but there are things that can be done to minimize the excruciating pain one has to experience at times.
 
I reported last time that the thermostat job was completed..WRONG! Things are working fine now but here is additional information. Since the service manual is incorrect there are no pictures or explanations on how to install a thermostat. When I removed the old thermostat I installed it the way the original was installed. WRONG! In retrospect the problem was that the old thermostat had dislodged and was not seating properly, hence too much coolant was passing through.
First, the location of the thermostat is on the bottom of the heat exchanger forward of the elbow that is in line with the coolant fill cap. Between the t-stat assembly and the elbow is a 90 degree hose elbow. You need to unbolt the metal elbow below the exchanger, remove the 90 degree hose elbow and the hose on the other end of the t-stat assembly. You now need to remove the t-stat assembly that is bolted to the block. You now have access to the t-stat. The t-stat actually "locks" into the assembly. It needs to be placed in the assembly properly otherwise you will not get an appropriate seal. There is a weep hole that needs to be strategically placed in position. To lock the t-stat in you need a large socket with a rubber material between the socket and t-stat to give you friction and a breaker bar to turn as you apply downward pressure.



The first picture depicts the t-stat top properly seated in lower protruding nib, which is on either side of casing.

The second picture depicts the underside seat of t-stat. notice location of weep hole. This is important.

The third picture shows small rubber piece cut from one of those jar opening rubber mats. Wife was a bit mad that I cut it up. Sorry about it being sideways.

Fourth picture shows large socket with breaker bar. Press and turn. Again, sorry for the sideways picture.

There are some important tips for removing the bolts. You need a good sized mirror, about 6 x 6, Allen wrench sockets 6mm, and a 6mm regular l shape allen wrench, a 13mm box wrench, 1/4 inch drive ratchet, 4" extension and a universal joint. There are two bolts on the heat exchanger that need to be removed to access one bolt on the metal elbow and one bolt on the t-stat housing. There are other incidental tools as well. You also need to drain as much coolant as possible. And by the way, you will be doing all this while looking at your mirror facing up as you work. A perfect fit for someone who is dyslexic Hopefully you will never have to do this, but feel free to contact me for additional info and I can talk you through it.
This is a two man job!! Thanks a million to Brian Beltrami of Gansett Ranger. He has lived through this entire project with me. We are now blood brothers!! :lol:
 
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