Overheating

I have fitted up and worked on hundreds of twin rigs and called them indicators as no two gauges ever read the same

 

No ... there is no bi metal sping in a temp sensor its a NTC material and its held in place and contct is made to it by a simple coil spring .

some designs of Oil pressure senders can have bi metal within them but not temp senders

 

But if you replace everything in pairs when only one is faulty you are essentially doubling your replacement parts cost. Your car doesn't have a second engine to compare engine temperatures with, and there are plenty of single engine boats as well. You can achieve perfectly acceptable diagnostic information by comparing an engine's temperature to it's own history.

 

I have the same problem with both my 5.7 lt Mercruisers 255HP.

If I run at 1200 RPM they both run at about 1/4 all day. If I take them up to 2000 RPM the temp rises to 1/2. Anything over 2000 RPM and they start to climb up to 3/4.

I too have replaced risers etc.

One thing of interest is that I can't get them to rev over 3000 RPM.

They should rev up to 4200 RPM, which makes me think if could be a prop problem.

What do you guys think?

Thanks

 

If you're not reaching your target RPM it's very probable that it's a prop problem, likely too much prop to be precise.

 

Thank you for the reply.

Would anyone know what size props should be on her.

The boat is a 31' Mariner, Australian built. It's similar to a Carver or a Bertram. For those who are unfamilar to the make.

Approx weight is 7 tons. I have no idea what the gearbox ratios are, other to say they should be original, and I can't see any sizes or markings on the props.

The current props are three bladers.

Thanks