2GM20F - How long for FW temp to rise above 100F?

[tmaccabe]

Hello, I'm troubleshooting my gauges after both oil press and water temp pegged high during our last outing. Slowing brought both down (all of a sudden) and speeding made them peg again suddenly (and they wouldn't come down again). We were close to the slip so we didn't run long like this.

This is a new boat for me and my first inboard/diesel, a 1986 Pearson 303.

I just finished re-doing the connections at the gauges. Oil reads 20psi when system is off and 40psi when engine is running. My water temp gauge sits at about 165F when the system is off (battery switch is off as well). When I start the engine the temp pegs low at 100F. I sat there for over 5 min running the engine but the needle never moved. I don't know what to think. I put my hand on top of the heat exchanger afterwards and it wasn't too warm to touch, barely hot. Probably 105F if I had to guess. How long is long enough to see temperature rise? I'm thinking of closing the raw water seacock for testing. Advice?

 

[Charles Erwin]

Oil pressure and water gauges with this motor means they are aftermarket - not Yanmar. So senders and wiring are add ons. Oil and water gauges senders should not peg in unison (ie both pegged high). If the wires from each sender were somehow shorted to DC negative both meters will peg. So follow the sender wires to find the DC neg fault. As to oil pressure and temp - with ignition off, engine off both gauges should show 0. Ignition on, engine off, engine cold they should move slightly upward but still show essentially zero. What brand gauges? Are these gauges new? If so, do you have euro senders mixed with US gauges - or vice versa? If not new, did they work differently before? Did you make certain dash lights, DC positive, DC negative and Sender feeds are not mixed up at the gauge posts? If DC positive is connected to sender post the gauge will probably be permanently damaged

 

[tmaccabe]

David, just got back from the boat. I ran engine with raw water closed until FW was hot to the touch. No increase at the temp gauge. Sender wire shows good continuity and gauge pegs high if I short the sender post to ground. Sender was reading about 350 ohms post to ground with engine warm and climbed to 400+ as it cooled. My understanding is it should have read <50 ohms when hot. I'm going to order a new sender and gauge to make sure they are compatible. The gauges are old. I can see that they are aftermarket because some yahoo installed them using T-Tap splicers right up close to the wiring harness connector for the engine panel. I added a better ground to the circuit but I'm not sure how to improve the connection coming from the engine switch. Doesn't appear to be an issue so I may leave it be.

 

[Johnb]

If you close your raw water off for too long you will burn up the impeller and ruin your day.

The only time you do that is if you are cranking a lot and don’t want to risk flooding the engine. Then you open the through hull as soon as the engine starts.

 

[Charles Erwin]

Here is some reliable data:

 

[kappykaplan]

Here is some reliable data:

Where?

 

[Charles Erwin]

Ooops