Click for Cheoy Lee List Your Boat Click for Cross Click for Lurssen Click for Glendinning

6v-92 thermostats

Discussion in 'Engines' started by Capt Bill11, Apr 14, 2018.

You need to be registered and signed in to view this content.
  1. Capt Bill11

    Capt Bill11 Senior Member

    Joined:
    Feb 27, 2006
    Messages:
    1,450
    Location:
    Sarasota/Ft. Lauderdale FL
    Pair of 6V-92s with the fuel/boost coolers that for the most part will be run at lower RPMs.

    Is there any advantage to changing the 160 degree thermostats to 180 degree ones?

    Especially in lieu of the fact that they have the fuel/boost coolers installed.
  2. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    10,035
    Location:
    Satsuma, FL
    Should be 170s. What temps are you reading with IR at the thermostat housing tops?
    Assuming TA's.
    As we have repeated, slow down to save fuel, open them up from time to time to clean the slobber out.
    Fuel coolers usually cool the fuel before tank return.
  3. Capt Bill11

    Capt Bill11 Senior Member

    Joined:
    Feb 27, 2006
    Messages:
    1,450
    Location:
    Sarasota/Ft. Lauderdale FL
    Thanks I’m aware of the need to run them up periodically.

    But it’s my understanding that because of the fuel/boost coolers on the 550 up version of the 6V-92s that the coolant water gets extra cooling from the fuel/boost cooler and because of that changing to higher temperature thermostats may not help get the engine temperatures up at lower RPM
    as they do on engines with just the fuel only cooler.

    Looking to see if anyone has any real world experience with running with the 180s.
  4. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    10,035
    Location:
    Satsuma, FL
    I'm thinking the cooler your referring to is the air charge after cooler heat exchanger. It probably does cool fuel.
    Some engine coolant is diverted to it and cools it again with the first flow of cool raw water. This now, real cool coolant is then pushed thru a air cooler (after cooler) under the blower, cooling the air charge rite before it's blown into the lungs. Cool air is more dense, more O2. The flash may be hotter and more complete.
    After cooling down the air charge after the turbo and blower, the return coolant can be pretty warm. The engine coolant then rejoins the motors circulation before the main heat exchanger.
    The engine thermostats does not control the temperature of the after cooler.
    If your motors are not coming up to thermostat opening temperature (your notes 160) during operation, you may be replacing them anyway.
    Those IR guns sure are handy vs trusting old remote gauges.
    You probably will never see your thermostats open up at dock side.

    I got a lil long winded here not to preach to you, but to ensure were on the same page and help others under stand.
    I also would like to hear from anybody that has experimented with different thermostat specs.
  5. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    10,035
    Location:
    Satsuma, FL
    BTW; The 12V71TAs and TIs we work on (including our TIs) use 170 degree thermostats. Their making HP for a while before all four of the thermostats are wide open.
    It is interesting our loaded temperature is 180 on all, at speed.
  6. Hall Engine

    Hall Engine New Member

    Joined:
    May 29, 2019
    Messages:
    4
    Location:
    Fort Lauderdale
    180 is great!
  7. MBevins

    MBevins Senior Member

    Joined:
    May 23, 2008
    Messages:
    775
    Location:
    Windsor On. Canada
    Same topic,
    On my 6-71s the t-stats open at 170 , what is the temperature we should expect them to close again?
    When I run at speed they open as requested however when I drop down to 900rpm the temp drops to 120° and stays there causing them to run cold.
    To me they should close again allowing my engine to stay closer to 160°.
    Also if I just stay at 900rpm from initial start the engines run at a nice 160 which I think is pretty good.
    This comes into play because I speed up to "clean out the slobber"
  8. Capt Fred

    Capt Fred Senior Member

    Joined:
    Jun 22, 2009
    Messages:
    298
    Location:
    Long Beach CA
    On my 6-71 TIs the t-stats open at 170, will regulate temp around 175 to 180 dependent on load but even at 700 rpm for trolling, maintain 170.
  9. MBevins

    MBevins Senior Member

    Joined:
    May 23, 2008
    Messages:
    775
    Location:
    Windsor On. Canada
    Thanks, this is why I think my stats are buggered. One is worse than the other.
  10. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,977
    Location:
    Fort Lauderdale
    I have run a lot of detroits that wouldn't stay at temperature under 1000 rpms. They wouldn't run as cold as yours, but then again most of the ones I ran were in FL water temps and would generally run 130-135 F under 1000 rpms...…..
  11. chesapeake46

    chesapeake46 Senior Member

    Joined:
    Jul 26, 2009
    Messages:
    1,629
    Location:
    Chesapeake Bay, Delaware Bay & S.Jersey
    I thought Thermostats did not " open" & " Close" 100 % but gradually opened and then restricted the flow to maintain temp. In other words they may open 100 % under full load and then restrict to maybe 60% flow when trolling, thereby keeping the temps pretty steady.

    That leads me to believe that the stats need to be replaced on yours, MBEVINS.

    Am I wrong about the stat operation ?
  12. Capt Fred

    Capt Fred Senior Member

    Joined:
    Jun 22, 2009
    Messages:
    298
    Location:
    Long Beach CA
    Chesapeake46, you are basically correct. On my 71s the stats are nearly 100% closed when below the operating temp. When I got my boat, one engine would not hold temp, It had to be loaded to get her to warm up. I removed the stat and found a small piece of metal had lodged in the stat. I removed the metal and she now holds temp. Never determined where that metal came from. I'm in the camp that believes that something is wrong with MBEVINS stats.
  13. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    10,035
    Location:
    Satsuma, FL
    Raw-sea water temps and cooling design have a lot to do with block temps.
    My 12s cool off to around 150-160* when not running hard.
  14. MBevins

    MBevins Senior Member

    Joined:
    May 23, 2008
    Messages:
    775
    Location:
    Windsor On. Canada
    I would agree with you however no matter what the seawater Temp is the stat should not allow the engine to drop down to 120° within 5 minutes of coming off plane.
  15. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    10,035
    Location:
    Satsuma, FL
    The stats very well may be closed at 120*. There are by-passes that keep coolant ALWAYS moving.
    These by-passes and a H/D heat exchanger probably can cool the motor off to 120*.
  16. MBevins

    MBevins Senior Member

    Joined:
    May 23, 2008
    Messages:
    775
    Location:
    Windsor On. Canada
    Again would agree but the starboard engine cools to 25° cooler than the port. So I keep coming back to the stat.
  17. MBevins

    MBevins Senior Member

    Joined:
    May 23, 2008
    Messages:
    775
    Location:
    Windsor On. Canada
    Are there different temp ranges for these stats?
  18. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    10,035
    Location:
    Satsuma, FL
    I have 4 stats per engine. When we rebuilt the stb main 15+ years ago, new stats went into both engines.
    All fresh 170s.
    The further up the St Johns river, we find more cool spring water.
    Just at a fast idle, say 1000 to 1100 RPM, south of Astor, I don't think our 12s read over 120*.
    I had to clear some grass from our thru hulls once, super quick time under the water, darn cold and gators about.
  19. Capt Fred

    Capt Fred Senior Member

    Joined:
    Jun 22, 2009
    Messages:
    298
    Location:
    Long Beach CA
    It really is not that hard to check the stat if you can get to the top of the engine. Drain a little coolant, pop out the stat and inspect. If all ok, put the stat in water and heat watching the temp of the stat with an IR gun or thermometer. The stat should begin to open around 170, be fairly open at 180 and fully open at 185. Then cool the water slowly and watch how it closes. It should be fully closed at 160 or above. These are approximate number. If your stat follows these numbers then it is ok, if not replace. Get a new gasket and replace the stat add back the coolant and start the engine and check for leaks. I'm pretty sure the stat will only go in one way but the spring part goes toward the engine side of the water flow. Alternately you could consider changing the stat and coolant with fresh stuff. If you do, drain the system and use proper coolant and distilled water.
  20. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,977
    Location:
    Fort Lauderdale
    If I'm going to pull something as cheap as a thermostat, I'm going to just replace it.

    Last year, I came across overheating issues on a set of 6v53's with about 300 hours SMOH, but they had some years on the rebuild. So the mechanic pulled the heat exchanger end caps and they looked great inside the bundles. That was until he pulled them out of the housing, the coolant side was chaulk full of sediment from the coolant and the bundles were clogged halfway up on the coolant side. Moral of this story is I am a very strong believer of changing coolant every 2 years!