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Glenn Simpson
Member
Username: trackhappy
Post Number: 13
Registered: 07-2009
| | Posted on Sunday, October 04, 2009 - 09:04 pm: | 
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I have just changed the thermostats in both my 4236's because they were running cold. It has fixed one, but the other still does not go much above 130. The gauge is accurate As I have checked with a laser gun. So given the new thermostat, what else can make her run cold??? Pump not set right? Injector pump timing? (How do you set it) Injectors?
High idle is 2750 approx, she seems to pull almost as well as the port does (similar RPM loaded flat out).
I note the oil runs through the heat exchanger, could there be too much flow there? (Oil pressures are fine and both similar). The head and block are pretty cool. There is no way the water can bypass the thermostat that I can see, so she must be generating less heat then the port baby. She has a water heater loop, but I have that shut off for testing
Any suggestions? |
Bob Slawson
New member
Username: bslawson
Post Number: 2
Registered: 03-2009
| | Posted on Monday, October 05, 2009 - 06:03 am: |
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can the thermostat slip out of position as you put the cover on? They can if the surface is vertical - like it happened on my 6354.
bob |
nat wales
Member
Username: bigtimeoperator
Post Number: 8
Registered: 08-2008
| | Posted on Monday, October 05, 2009 - 10:41 pm: |
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Hey Glenn,
I'm not sure I will be able to offer anything else. It does seem likely that it's something keeping the thermostat open or that it's not seated properly. Could debris get lodged in when the thermostat is open preventing it from shutting? It also seems surprising that BOTH of your engines were running cold like that. Did you determine that the cause was definitely the thermostat in each engine and could you see that they were both defective? Is it possible that you got one of the bad ones mixed up? I can't think what else would cause the engine to run so cool.
I assume these are running under a load an not just idle? The boat is running straight, yeah? My single 4.236 doesn't get much above 130 unless it's under load and turning at at least 1500 rpms. Also, 2750 seems high. I cruise at 2000 and max out at 2200. I was told to never go to much higher than 2000 on this engine.
Let me know if you solve the problem. Also, I'd love to know how you have your hot water heater piped up. I'm considering putting a heater in my boat this winter, but I'm not sure exactly what ports to tap into. |
Glenn Simpson
Member
Username: trackhappy
Post Number: 14
Registered: 07-2009
| | Posted on Monday, October 05, 2009 - 11:59 pm: |
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Hi Nat,
It is a bit confusing. If I only had one engine (no comparison) it probably wouldn't worry me. No chance I mixed up the thermostats, but I guess I will have to check now that you have mentioned it  . Even under no real load, just sitting at 1200 rpm the Port engine will eventually warm up and sit right at thermostat temp. Thats the behaviour I expect of most diesels, as the thermostat lets very little through until it opens up.
These engines are rated at 85 HP at 2800 RPM from what I can find (Also seen quoted 72HP at 2600 RPM, but not official). High idle (governed maximum rpm) at 2750 seems spot on. Everything I have been told is that if the props are right size, you should be able to approach high idle speed running flat out. If you can't, then she is overloaded (that holds true for most fixed duty engines, if you manually open the throttle and she doesn't speed up, there is too much load). Mine maxes out at 2100 at present, thats quite a bit down on what it should be capable of - not that I run like that though, just should be able to. Possibly, 1800-2000 might be the best economy speed for these babies, but I have not seen a chart and it depends on load. Another school of thought seems to be to load them down for cruising at lower rpm for the same speed (if you have excess engine HP). I don't much like that idea, as it seems to be purposely overloading an engine. This old gal used to have larger Cat diesels, and I am guessing they didn't change the props. I initially assumed that they had not got thermostats in them. Turned out that they had them, just 68 deg. ones. They now have 78, which is closer to the recommended 82. Port responded properly, Starboard didn't. One other thing I should mention, since I fitted them, the Stboard isn't reaching the same RPM as the Port. I adjusted the stop cable, and I suspect I did it up a wee bit too much so she isn't feeding as well as she should. I'll check that first to see if it makes a difference.
As for the heater circuit, I'll check exactly and get back to you. Maybe a piccie or two if I can. The heater pipe returns from the hot water service via a valve, to a nipple on the starboard side of the header tank, and feeds from an elbow on the water pump (before the thermostat, just like a car heater). That makes sense, as the hot engine water heats the hot water unit, and when it is hot, the thermostat opens to let more out to the heat exchanger as required. (Get out of trouble tip # 23 here..... raw water restricion, engine overheating, turn on the hot water tap).
Thanks Bob, the surface is horizontal and the hole above is much smaller so it pretty my can't move.
I should be back to her on the weekend for further investigation. Honestly, I am just an engine perfectionist. I believe manufacturers supply speeds and temperatures for a reason, and running an engine contrary to them just seems wrong. Think about this.... if they were under warranty and you told the dealer you had them running cold and overloaded, what are they likely to say???
Love a good mystery!!! |
Glenn Simpson
Member
Username: trackhappy
Post Number: 18
Registered: 07-2009
| | Posted on Sunday, October 18, 2009 - 07:28 pm: |
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Ok, heating circuit is easy on this engine. (Well, apart from having to remove the heat exchanger to add the elbow).
On the engine fresh water pump, just below where the big hose comes off there is a vertical flat spot which is tapped and an elbow screwed in for one hose to the heater. The return goes into a tapped hole on the left hand end (looking from the front) of the header (Bowman heat exchanger) tank. In a photo in the manual it seems this normally has a plug installed.
Hope this helps. |
Glenn Simpson
Member
Username: trackhappy
Post Number: 26
Registered: 07-2009
| | Posted on Sunday, November 15, 2009 - 01:47 am: |
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Ah Hah!!!!
I pulled the header tank/heat exchanger off and looked carefully. The hole above the thermostat had corroded just enough to be bigger than the thermostat O.D. when the engine started, the thermostat was pushed up into the hole and the water bypassed it. Made a stainless plate to go
in between and Voila!.
Thanks for everybody's input. |
crzhors
Member
Username: crzhors
Post Number: 54
Registered: 09-2006
| | Posted on Sunday, November 15, 2009 - 08:22 am: |
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Glenn, Great detective work! Thanks for sharing your cure.I'm constantly finding these strange problems and doing the forensics to cure them.I'd like to start a "Frustrated Mechanic forum" where we can vent and commiserate... JD |
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