Reckless32

See the email below of a friend of mine (SuperHawaii 40) who put this out to our club who is having this problem with one of his 502's. Any suggestions?

"Please let me know if you might know why one of my motors would all of a sudden be showing a lower temp on water. Not only lower but it would fluctuate from 145 - 120 and go as low as 105 when under hard 5100 RPM's. (Drew ran them full throttle from Hampton to Little Creek chasing down Tommy Kimball and they both ran like a champ, the one was 165, the other, 105 when we got there to climb to 150 when we came off plane in the no wake zone) The faster the RPM, the lower the temp. Stop and let it then sit (keys on, motor not running) and it climbs up to 175. Start it, down to 145 and on & on.
All this time the other motor is 165, up 7 - 8 when running hard. The first used to.
1. Changed Thermostat (165) Still cold.
2. Flushed engine and replaced with a second new thermostat in case sand might be persistent.
3. Flushed engine (with Dave Lauterbach's help) and put in a third thermostat to make doubly sure it can't be that.
4. Pulled and changed both Sensors with each other.
5. Wired the sensor to the other motor's gauge.
THIS MACHINE IS RUNNING TEMP SHIFTS I CAN'T UNDERSTAND. It takes it 3 - 4 seconds to come from the 175 sitting temp after a long hard run to 115 if I start it and put the throttle down.
I know its cold, Better then hot, but it never did it before and started instantly.
Give me a clue! "

Gary Anderson

Did he try the simple stuff:
Change the impeller, backflush the oil cooler, check the raw water & recirculating belts for tension, glazing, blockage in bypass circuit. Stranger things have affected water temp.
Gary

MESABALANCING

Looking Towards The Simple Stuff Do Both Engines Run The Same Water Press. If Not It May Be As Simple As Perhaps A Worn Belt Or Even A Worn Impeller.good Luck Laz Mesa

robyw1

If the seawater pump checks out okay, you might be drawing air into the cooling system from the circulation pump. When the engine of concern is running how much water is coming out of the exhaust? Are both the same? If so you need to look at the circulation pump. You see the sensor will detect air temperature cooler than water. This is bad because in actuality the engine you think is too cold is actually on the brink of overheating. First thing to look for is a hose collapse on the intake of the circulation pump. The cause of this is the increased vacuum draw on the hose as RPMs come up.

Roby

rookie_j

bad guage or sender?

krypto 1 in CT

yep,sounds like the sending unit is seeing some air.

J-Bonz

Did some one try physically touching the pipes to see if there is a change in temp between stb and prt?

dykstra

sending unit

Bryanw

I would check for a bad sender. If you have access to a infrared temp sensor you can check the temp of the intake and blocks on both motors. I use one on my drag car on a regular basis... If you see that quick of a temp change I'd guess the sender is seeing air. Try switching the sensors from side to side and check if it still happens on the same engine.

28SS

Maybe thermostat staying is staying open.
This dosn't give block enough time to heat water in block
cause water pressure moving water through block to fast.
This also could also cause oil temp to rise