[Jeff Barnett]

Hi folks,
I was just wondering what water temp your engines run at. my 96 Z255 with a 2000 7.4 mercrusier seems to stick around 175 degrees, maybe a tad over if I'm running it hard. I'm just curious to see what water temps other engines are running. 175 is great for a BB chevy in a car application, but I have no idea if thats considered good for a marine engine.

[MariahMan]

The Volvo 5.7 GXi in our boat runs just a hair under 175. The needle is always sitting literally just under the mark for 175. It has never gone higher. When we bought the boat the dealer said if it ever goes above that mark to shut it off for fear of overheating.

If we use the heater we installed in the boat the temp drops, but otherwise the boat engine stays just under 175 consistently.

[ShabahZ250]

My boat's got the 7.4L MPI in it, and it runs consistently at 175. The Mercruiser manual states this is the optimum temp. Anything above that and you're starting to get into overheating territory.

[Z 202]

Depends on the time of year. In May it runs well south of 175, but then the lake water is only 4 or 5 degrees Celcius.

August it runs closer to 175 but never quite on the mark.

[moondance100]

ok, I"m convinced....I need a thermostat!! Mine runs much cooler....probably 115 to 120....not warm enough!

[KSP181]

Mine runs 175 even.

[mikeyt]

me thinks we have a concensus here. 175 it is! Now is that Celcius or Farhenheit?

[schweddy]

Originally Posted by moondance100

ok, I"m convinced....I need a thermostat!! Mine runs much cooler....probably 115 to 120....not warm enough!

You run without a thermostat?! Don't want to flame or anything... but...

#1) 115-120F is WAAAAAYYYY too cold for internal combustion engines. Engines are designed for an ideal operating temperature where all tolerances are as close to ideal as possible. Running too cold increases wear, and decreases the efficiency of your engine. A good general rule is 80C or about 175F.

#2) Not sure what engine management you run, but modern EFI systems are tuned at these "normal" operating temperatures, and a pretty simple calibration curve is set to bias fuel according to engine temperature. Yes, the amount of fuel going into your engine needs to change dependent on engine temperature in order to retain maximum efficiency.

#3) What is the highest temperature the water you run in ever reaches? Probably never within 30-40F of 115-120F let alone the general 170-180F "rule". This means you are pumping in COLD water right into your block, which means that some parts of your engine are running a lot cooler than others. Big temperature gradients are bad.

In some situations you can get away with running sans thermostat, like if you have a radiator. However the correct way to do this is to size an orifice in place of the thermostat to obtain the correct coolant flow levels through the radiator.

Get one in there right away...

[indykoch]

I'm guessing Doug meant he needs a "new" one, but I'll let him answer that. I just hope it hasn't caused premature wear to that bad boy 502!!!

I'm checking mine today, but I believe it's right under the 175 mark as well.

[boatman]

I have the 5.7L, and it runs just under 175.