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Thread: High Oil Temp

  1. #1
    Need a little help,I run a 540 merlin with ext oil cooler.Over winter my oil temp would run 190 at high rpms water temp wouldnt get over 100 thought my water temp guage was bad tested guage and even replaced sending unit.two trips ago oil temp was up to 250 water was the same,I replaced the water pump impeller,Last trip oil temp ran 250 the water temp ran 105.I was told you dont want your oil temp any higher then 220. Is my engine running so cold that all the heat is going into the oil? Any HELP would be great.

  2. #2
    the water is also warmer now so it cools the oil less. make sure no clogging going to the cooler, but no, the cold engine won't make the oil hot. on easy cruise about 40 does the temp still climb that high or just when gettin it?

  3. #3
    It tops out at 250-255 The slower I run the cooler the oil temp,I get back down to idle the oil temp goes back down to 100.Im going to pull the oil cooler off maybe some sand pluging up the water flow.It just seems the water temp should be hotter then 105.What do you think is to hot for oil temp

  4. #4
    It runs 250 at 50 mph the boat runs 85mph top speed I didnt try and push it any harder.

  5. #5
    I agree that something may be clogging the oil cooler a bit but I think you'd have a happier engine running just a tad warmer. 100 is really cold, IMO a bit too cold. My jet is kind-of backwards as cooling goes with raw water cooling but I have a flat-out running temp of 130 to 140 and an idle temp of 170 (due to less water flow from the jet at idle). I wouldn't want my running temps any lower than 130 in any case. Your oil DOES need to get above 212 though in order to keep any condensation moisture boiled out of it. Personally I wouldn't sweat an oil temp of 250 as long as it stopped about there as I would just run synthetic (as I do in my jet). just my $0.02

  6. #6
    My cooling system is raw also no closed system.Thanks for the help.

  7. #7
    Oil cooler is not pluged up. Need to install a presure guage in the system were is the best place to install sending unit?

  8. #8
    Dunno a merlin block. On a Chevy block there is a row of small plugs along (at least) the left side of the block, each one lined up with a main bearing. If the merlin has these, they each tap into the same oil gallery feeder. Any one would do. I am running my backup mech gauge off the front one and my dash elec off of the sender location above my oil filter stock location.

  9. #9
    Thanks for all your help but I mean a water presure sending unit

  10. #10
    I install oil temp gauges on all the boats I build. Oil temp is more accurate then water. Water passes thru so quickly it cant absorb the heat. Oil temp should max around 220 under normal running. But will climb to 250+ under long hard runs. One thing forsure is you know you have "GOOD" oil temp!!!! Many engines have selfdestructed because the "INERDS" have not warmed up to normal temp ranges. Just make sure there are no blockages in your cooling system and you should be fine.

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