Trouble shooting Engine Temp

I just changed my impeller and did a 65 mile run the Other day...boat ran perfect. I noticed a temp of 170 degrees....then 160....and around 150. Water temperature was 80 degrees then 73 degrees during the run. Is there a test for the sending unit, the gage, or the thermostat? Engine is cool but it bugs me as it is not working correctly!

Thanks!

Otto

Ok Great...I assume that sits right on top above the center fully? Also, can I use a thermostat I pick up from the auto parts store for a Ford 351?

It will be nice to change the too so i will know the time on each component!

Thanks!

Otto

Chris,
I wouldn't condemn the T stat just yet. Considering what you just went though with your alternator/battery problem only to find bad connections, I'd suggest checking the circuit for the temp sender and temp gauge too. Get that VOM out again and check the Ohms.

Yes, plus 1 on the IR gun. Have you checked the temp with one?

Also understand that engine temps will vary depending on how hard the you're running the engine.

8122pbrainard wrote: Chris, Also understand that engine temps will vary depending on how hard the you're running the engine.

What he said

And I don't know why Jonny is stuck on a 160 degree thermostat if you're gonna replace yours.

You could very well have a 143 degree in there, being a raw water cooled, carbureted, PCM 351. The 160 degree ones were in the fuel injected engines.

And if you don't have a 143, maybe you should. Once it's open, your temperature will depend on load on the engine, injection temperature and response time to go from one let's say steady state condition to another.

If that big hot hunk of metal known as the engine is run hard and you come down to idle, temperature will go up since your cooling water flow has been cut back from around 20 gallons/minute to 5 or so gallons/minute and it has to cool off that hot hunk of metal which will take a little time.

You may have nothing wrong at all, but if you check with an IR gun you'll have a good idea whether the gauge is right. Aim it right at the manifold where the temperature sensor is located to compare it to the gauge.

There's bound to be a little difference due to heat transfer through the metal of the manifold as compared to the sensor being immersed in the water,sensing the water temperature

Otto Throttle wrote: Was running nicely today at 150 degrees...could the improved flow of the new impeller Improve efficiency like this? Going to try and find a temp gun today... Great points being made... my new multi meter will get some use too! I am going to order a spare thermostat as well... being in OH and running in water temps from 60 to 80 what are the pros and cons of the temperature choice ? Before taking off the thermostat housing (mine looks like it has Allen head bolts), should I take off the hoses or can you just loosen the clamps and have enough room to work. Thanks to all that are helping! Otto

The new impeller can definitely help.

It's easier to take the housing off if you take off the hose that goes to the left exhaust manifold, then you can flop the housing over to the right with the other hoses still attached.

I think you're looking for a problem that may not exist, but if you're getting a new thermostat get a 143   

Otto Throttle wrote:    I am going to order a 143 thermostat just to have on hand.... Otto

Chris,
Have you confirmed or know what temp T stat is in there now? If it isn't the 143, then change it to the 143. That's the correct one.

I'm running a 143F thermostat on my 93's 351W..and my temps are a pretty constant 125-130F no matter if I am running at idle or WOT.

Dan

take this for what it's worth. From all I have read and have heard from others who have run both the 143 and 160f t-stats is that there is a LOT of starting and stopping with a marine application and when you turn the motor off...cooling is gone. the higher temp thermostat can let the engine head temp get well over 200F. as opposed to a close system with coolant.

also, the water flowing around the engine can start boiling, and when it gets that hot it creates vapor or steam pockets, and those pockets dont conduct heat away from the engine, so to reduce that temp, they installed the 143F T-stats to lower the water temp in the engine. The trade off for going from a 160F to a 143F is a bit lower fuel economy.

Now...again, this is only what I've been told, so take it at face value.

Interesting as my engine is running around the 140-150 range, so that may be normal for this thermostat set up. I was told 180 is the normal range which is why I was questioning the temperature to begin with. New impeller is better efficiency is lower operating temp...what effect is noticeable when running higher octane fuel...I am running 93?


Otto

A real quick and free check, make sure your water strainer is free of junk, that the o ring is in place, and that it's screwed on snuggly.