Thermostat 454

[northern]

We have twin 454 year 1989 3600 hours. Uses 1/2 Qt every 100 hours Port engine at 1200 RPM temperature fluctuates from o on gauge to 190F when it gets to 190 it drops to 100F. The Starboard engine goes to 160F at 1200 RPM and stays there. At 1600 RPM Port goes to 180 fluctuates to 190 never drops lower than 180. Starboard goes to 160 and stays there constantly. Both engines have 140F thermostats in them. Both changed 300 hours ago.
Any idea what my problem is?

 

[northern]

Both engines cooled by antifreeze risers and manifolds replaced 150 hours ago. Boat in salt water on west coat

 

[blaster]

Have you recently replaced the thermostats? Is one possibility installed upside down?

 

[northern]

Have you recently replaced the thermostats? Is one possibility installed upside down?

It is not installed upside down. I followed the service manual and both were put in the same way. it has 150 hours on each

 

[northern]

Went and got 2 new thermostats with all the gaskets one from NAPA and one from Sierra. Both gasket kits have the by pass hole around the thermostat blocked off. Is this correct there is no hole in the thermostat face.

 

[km1125]

You didn't mention anything about impellers or heat exchangers. When was the last time either was serviced and what was their condition at the time?

 

[electricaldoctor]

Although your hot water tank is electric, it also heats up the water from one of the engines and therefore affects the operating temperature of that engine. This would explain the difference in the readings of your gauges.

 

[km1125]

You might also want to get (or borrow) an IR temp gun to verify that the readings you're seeing on the gauge is what's really happening on the engine.

 

[Scott215]

3600 hrs, wow that's insane

 

[Scott215]

I have heard a lot of weird stuff about the temperature gauges and sending units lately so the IR is probably the way to go pointed at the thermostat housing and see what your actual temp is

 

[Pirate Lady]

3600! My god. I got a 91 454 with 600. Guess i good for a while.

 

[Scott215]

Another 40 years bud

 

[northern]

You didn't mention anything about impellers or heat exchangers. When was the last time either was serviced and what was their condition at the time?

All new heat exchangers 2 years ago. New raw water pump impeller last fall. Good water follow

 

[northern]

You might also want to get (or borrow) an IR temp gun to verify that the readings you're seeing on the gauge is what's really happening on the engine.

Did that and they are correct

 

[northern]

3600! My god. I got a 91 454 with 600. Guess i good for a while.

I use Shell T1 SAE 40. No idea if that is good or bad but manual says to use SAE 40 not multi grade oil

 

[Jimmy Buoy]

Might not be your issue, but wild temp fluxuations diagnosed using clear hoses. Might be worth a look.

 

[northern]

Might not be your issue, but wild temp fluxuations diagnosed using clear hoses. Might be worth a look.

Thanks looks like it might be problem