Trojan Boat Forum

Trying to figure out the proper operating temperture for my 76 F-28, w/318's. The engines seem to be running fine and the gauges on the fly and salon are reading the same. Im not even sure that I have a reason of concern but both engines are running around 170 degrees when warmed up and running WOT.

Friday I changed both impellers, starboard side the impeller was complete, but a couple of the veins was cracked. the port side impeller was in worst condition, missing three or four viens and others were split. got everything back together. and ran the boat for hour or so. the temperature stayed the same. I dont know what t-stats (temps) are in the boat.

Should I be concerned?? is 170 to hot?

at first I was concerned that pieces of the impeller may have gotten lodged somewhere in the system, but with both engines running the same temps, i dont think that is the case.

but like I said, the boat seems to be running fine. So any input would be great.

Freash or raw water cooled ?

Gets water from the lake. I'm not sure the diff between fresh water and raw

Raw water cooling (RWC) is lake water running thru the block for cooling. Fresh water cooling (FWC) is a closed system where coolant runs thru the block and then thru a heat exchanger which is cooled by lake water. Both methods are appropriate in fresh water, but FWC is the norm in salt water. Sounds like your boat is RWC.

If I recall correctly, Chrysler Mariine issued a service bulletin specifying a 140F thermostat for the M318.

Raw water cooled means the engine and exhaust both get cooled by water coming in through the raw water intake in the bottom of the hull and expelling it out the exhaust. Fresh water cooled means the engine has a heat exchanger (like a radiator without the fins) and sealed engine (seperate from the exhaust system) where the engine is cooled by antifreeze (coolant, like a car) and the exhaust is cooled by raw water coming in through the hull. Kinda strange because even though it's called fresh water cooled there is nothing fresh about antifreeze. To make a long story longer, if you have a heat exchanger on your engine with antifreeze in it you are fresh water cooled, if not you are raw water cooled.

Sorry jon_e, I posted before seeing you had it covered.

170 is what I was getting from my old thermostat at cruise speed... put in 160 deg thermostats and the temp dropped to 160 (the spec ones).... duh!!

I don't think 170 is too hot but cooler is always better......

Something to consider. There is an optimum engine temperature for gasoline atomization, therefore affecting performance and economy. Personally, I like to run my engines in the higher temperature range just for that reason. Without going into too much detail, I will say that newer cars run higher temperatures to help with performance and economy while burning less effficient fuels. Simply put, gas burned a little better 35 years ago but not enough to notice the difference in the lawnmower or driving the car around town.

I think 'factory' thermostat was 165 degrees in my 360s.

I've heard if you are running in salt water and you are raw water cooled you want the 140 degree themostat. Apparently, at higher tempertures, you'll get salt build up in the block due to the salt water starts to crystalize at the higher temps. If you are fresh water cooled you want a 160 degree themostat. If you're in a fresh water and don't plan on running in salt water, 160 degree thermostat would probably be fine for a raw water cooled boat.

My Mercs spec a 140 degree thermostat. Your owner's manual or maintenance manual should specify what temperature yours should be set at.

My mechanic recently replaced both of the thermostats and I questioned him about that very thing. He showed me the Mercruiser engine specification for my '79 255s and he was right on the money.

Thanks for the input! Mine is a raw water system, so I guess if both engines are maintaining tthe same temp there shouldn't be an issue, I'll keep an eye on the guages. Maybe change the t-stats end of season.
R

Just an FYI. Whenever you remove an impellor that has missing blades, they are most likely lodged in the cooling system and may come back to haunt you one day. Always back flush the system and try to recover as many pieces as are missing. In your case they may be at your oil cooler.

Big D, thanks for the reminder!!! where do I start the back flush?? at the oil cooler?? disconnect from the output of the pump and back flush form there? If I recal, there are three lines that go into the t-stat housing.

I thought the pieces would have blown thru the exhaust by know. there was a couple pieces lodged in the pump itself. but that left a couple missing.

I trust you have a single pocket pump (one impeller). The first item in the circuit should be the oil cooler/s. I suspect if there are any pieces, they would be there. Shut off the seacock, remove the outlet hose from the pump, remove the hose at the engine end that comes off the cooler and flush it from that end with a garden hose. If you can get the hose at the pump end into a small bucket, it will catch everything that comes out.