Offshoreonly.com - Water Pressure Bouncing!

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Q & A (https://www.offshoreonly.com/forums/general-q-20/)

- - Water Pressure Bouncing! (https://www.offshoreonly.com/forums/general-q/385314-water-pressure-bouncing.html)

Any suggestions for good Thermostats? High flow or whatever? Or just original 160F ?

Test drove her yesterday without Thermostst.
No fluctruating Water press. Idle 3psi, went up to 4200rpm @17psi. Engine cold, Manifolds hand warm.
I'm wondering if the thermostat was bad or if the fluctruating comes back with the new thermostat.

Quote:

Originally Posted by cig28 (Post 4925657)

35 is to high. With pressure getting high the water is not getting out of the engines fast enough. You could end up with intake or head gasket problems. I had this problem with my boat. Mercury had a solution and put out a service bulletin because of high water pressures. The solution was to put set screw in the side pickups on the bravo drives. My top 3 hole are plugged and the dropped my pressure down to 15-20 psi running wide open and 10-12 cruising.

I agree that 35+ is too high, and even questioned it when I bought my boat years ago, but my stock 502mpi's have close to 900hrs and haven't had any issues related to it. I have transom mounted water pick ups, so can't plug drive holes.

Quote:

Originally Posted by AP700 (Post 4925722)

I would try a new 160* OEM thermostat first. If it is still bouncing, I'd drill a 3/16" hole in the tstat and test again.

Drilling a weep flow hole in the thermostat, and getting some water flow in the engine as it heats up is good to have.

Cummins 5.9 engines has this weird temp fluctuation as the thermostat cycles. It's unnerving. I think Dodge changed the gauge to respond less.

Tried today. I took the original thermostat, drilled 2 holes 1/8. The water pressure does not fluctruating anymore but she would peg the gauge. Reved 4500 and had 35psi. Pulled back the stick then.
so whats the best solutuon now? Bypass?

Quote:

Originally Posted by AP700 (Post 4925843)

Like I posted above, my 502mpis will push 35psi + also. When I first got my boat with 250hrs, I was going to install pressure relief valves. I wasn't having issuies and never did install them. The engines have almost 900hrs on them.
You would need to either reduce the amount of water coming in or get a pressure relief valve to get it out faster.

What happened to trying a new 160° thermostat?

I would like to install a pressure relief valve. Whats the best place to tee in? CPPerformance has the T in 1-1/4 inch. Looks like it should be between seawater pump and oil cooler? I weld the T by myself so i can size it how i like it. so whats the best place to tee in?

Thanks!

After the oil cooler. You want full flow to the oil cooler.

Quote:

Originally Posted by fbc25el (Post 4926740)

After the oil cooler. You want full flow to the oil cooler.

Not sure what pressure he's popping of to, but wouldn't 35psi would pretty much be 'full flow'?

Then he's not getting surges on his oil cooler.