Temp Gauge Fluctuates

[yeahmag]

I'm not certain this is a problem, but for the first 20-30 minutes of cruising, the temp gauge swings back and forth from 170F-200F. This is a RWC engine with a Moyer thermostat in it. After extend cruising time, it settles in right around 180F.

My suspicion is the thermostat is opening and closing while then engine itself is still getting up to a consistent thermostat, but I wanted to get some other options.

Thanks

-Aaron

[joe_db]

Originally Posted by yeahmag

I'm not certain this is a problem, but for the first 20-30 minutes of cruising, the temp gauge swings back and forth from 170F-200F. This is a RWC engine with a Moyer thermostat in it. After extend cruising time, it settles in right around 180F.

My suspicion is the thermostat is opening and closing while then engine itself is still getting up to a consistent thermostat, but I wanted to get some other options.

Thanks

-Aaron

My previous engine would do that, it eventually got to going past 240
The long-term cure was another engine, but the short term cure was a good acid flush.
Best case is clearing salt, algae, dead fish, and so on will put her back to normal. Worst case is there is enough corrosion and rust that metal bits will keep getting loose and causing problems.
The other possibility is the thermostat has gone nuts, a quick test is to remove it and use a bypass valve.

[sastanley]

Aaron, I agree with joe...Take out the t-stat and see how it runs...if you don't totally tear apart the gasket in the process, you can just bolt the housing back on for the test, and maybe use some Permatex (#3 in the can with a brush) to help seal the gasket area and report back.
200°F is not too hot, but you are running out of margin much past that..most RWC'd motors are 150-170°F.

Do you already have the bypass valve on the 1/2" hose from the side plate that goes into the stbd side of the t-stat housing? You can simulate a valve (closing the flow in the bypass hose) to force the water up thru the block and t-stat housing with a pair of needle nose vice grips or similar tool.

[W2ET]

I think I'd clean up the relevant electrical connections, too.

Bill

[yeahmag]

Before my ownership it was run with (i believe) a non functional automotive style thermostat in the stock, late housing with no restriction on the side plate. In this mode the temp would never come off the stop, but I suspect that was a false reading and it was probably running quite warm as it blew a head gasket not long after I purchased the boat.

I have tried clamping the 1/2" hose before the thermostat to see if it made any difference and it did not. I've done some simple electrical diagnostics and nothing jumps out at me. I've also shot the head with an IR gun and all the temps look OK there. Obviously I won't see any fast fluctuations there due to the thermal mass of the head.

These fluctuations move quick enough (like 5-10 seconds from 200 down to 170) that I do suspect some sort of problem with the thermostat or the gauge.

Originally Posted by sastanley

Aaron, I agree with joe...Take out the t-stat and see how it runs...if you don't totally tear apart the gasket in the process, you can just bolt the housing back on for the test, and maybe use some Permatex (#3 in the can with a brush) to help seal the gasket area and report back.
200°F is not too hot, but you are running out of margin much past that..most RWC'd motors are 150-170°F.

Do you already have the bypass valve on the 1/2" hose from the side plate that goes into the stbd side of the t-stat housing? You can simulate a valve (closing the flow in the bypass hose) to force the water up thru the block and t-stat housing with a pair of needle nose vice grips or similar tool.

[joe_db]

Originally Posted by sastanley

200°F is not too hot, but you are running out of margin much past that..most RWC'd motors are 150-170°F.

200 is WAY too hot for a RWC engine. Anything past 140 and you get salt and mineral plating out at an increasing rate.
My current engine might maybe hit 140 if run hard for a long time in 85 degree water.
My old engine would start the year at 160-170 and get hotter every week it seemed. When it hit 200 or so I would acid-flush it and it would mostly go back to 160 until the corrosion got too bad one year and that was the end of it.

[Al Schober]

Have you considered relocating the temperature sender? I was never happy with my temperature readings and it seemed the the location of the sender in the head was in an area of variable water circulation. Readings seemed to vary from water temperature (with flow) to head temperature (limited flow). IR thermometers are a neat tool!
I relocated my sender to the outlet from the manifold. I put in a tee and screwed the sender into the side of the tee. Not once did I have an urge to move it back to the head.

[joe_db]

Originally Posted by Al Schober

Have you considered relocating the temperature sender? I was never happy with my temperature readings and it seemed the the location of the sender in the head was in an area of variable water circulation. Readings seemed to vary from water temperature (with flow) to head temperature (limited flow). IR thermometers are a neat tool!
I relocated my sender to the outlet from the manifold. I put in a tee and screwed the sender into the side of the tee. Not once did I have an urge to move it back to the head.

My temp gauge is also moved. The thermostat housing deadends with the temp alarm sensor, the water exits from the spot where the stock temp sensor used to go, it has a T, one branch has the gauge temp sensor and the other branch goes to the exhaust manifold.
I have used my IR on it enough times to know it is reasonably accurate.

[Dave Neptune]

Al, I did not like the warm and cold proximity to the sensor either and found it troublesome to get my bypass adjusted to where I could leave it alone at various speeds. What I did was to plug the bypass inlet to the t-stat housing and reroute the bypass to my exit fitting on the exhaust manifold via a "Y fitting". My gage fluctuations during adjusting of the bypass became easy and I was then getting accurate block temp readings and no longer needed an adjustment once in a while. I found my temps varied by RPM or water flow with the stock plumbing and not with the reroute.
A pic of my set-up was posted some years ago.

Dave Neptune