Outboard Temp Sensor
- Thread starter FourPoints
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Have a look at this website to see if it may fit your needs: enginewatchdog.com I've just purchased their TM4 dual temperature sensor model to install on my Yanmar 3GM30. One reading for engine temp and one for the transmission. I first saw it on a friends 1995 - 35.5, it was a single sensor model for engine temp alone. He swears by it to monitor engine temp. Installation is very simple, I'm looking forward to being able to know the temps on both the engine and transmission. Hope this site helps out.
Engine is a 1990, if it is easy to install I would like to have an alarm in case the water pump clogs and I, or whomever is at the helm didn't notice.
Hmm, that would be an easy solution. I could use the 2nd lead at the Batteries if I wanted that, or just go with the single. Any idea how much power it draws?
I had a temp sensor on a larger ob. -no alarm. its just a temp sensor touching the head connected to a gauge... it was helpful with a baseline temp, and when it got higher usually indicated a broken vane. not sure about wiring an alarm though.
Water pump impellers dont generally fail suddenly, and then almost not at all if replaced annually, or even bi-annually. They generally die slowly, with the first indication a slow to intermittent trickle at idle. Even when so bad they wont flow at idle, they will generally flow adequately with increased speed.
I dont feel its an issue worth worrying over if they are maintained.
I dont feel its an issue worth worrying over if they are maintained.
They don't frequently fail suddenly, but it does happen. Also you can get a plastic bag wrapped on the lower unit restricting water intake, or marine growth (less of an issue if you leave the engine out of the water most of the time). On a few occasions I have caught trash with the lower unit, thankfully it has never caused problems, and I would like to keep it that way.
Im just saying the water flow tell tale is a far better indicator of pumping function and cooling than any other means. But saying that, as well as my previous comments, I find Bills comments rather interesting.
If I were going to mount a guage, I would want it mounted on the motor itself so its all self contained. If you mounted a small mechanical gauge on a very stout metal (Stainless) bracket, you could arrange it so the hood would fit over it, and a hole drilled in the hood would allow you to see it. You should set the gauge in such a way the hood and gauge seal tightly against each other. I think rather than water temp though, I would go for a cylinder head temp off the upper most head bolt. Mechanical water temp gauges often drop when they are no longer submerged in water/coolant. A CHT gauge will indicate the temp of the bolt regardless.
If I were going to mount a guage, I would want it mounted on the motor itself so its all self contained. If you mounted a small mechanical gauge on a very stout metal (Stainless) bracket, you could arrange it so the hood would fit over it, and a hole drilled in the hood would allow you to see it. You should set the gauge in such a way the hood and gauge seal tightly against each other. I think rather than water temp though, I would go for a cylinder head temp off the upper most head bolt. Mechanical water temp gauges often drop when they are no longer submerged in water/coolant. A CHT gauge will indicate the temp of the bolt regardless.
Actually on many (most?) engines the piss tube water flow is independent of / before water flow through the water jacket, and as such provides zero indication of actual cooling flow through the engine. It does provide a clear evidence of water pump activity, but if you loose a spline from the impeller and it gets lodged inside the engine block restricting water flow, it could actually make the piss tube pump even more water than normal by the increased pressure resulting from the restricted water flow, even though the impeller is pumping less water.
If you want to see cooling flow, look at the water spitting out the two ports in the aft side center of the exhaust leg, that is cooling water output, but it is much harder to actually see from the boat or measure.
I don't have a typical small boat outboard setup. Specifically I have no tiller arm, any my engine is 100% controlled from the cockpit with electric ignition and remote shift / throttle controls, except for tilt which is manual. Also since I have a sugar scoop walk through transom my engine sits about 3-4 feet behind, and 12-18 inches below the cockpit and is fixed in position so it can't turn. Given it's placement it is difficult to even see when seated anywhere but the aft most seat. As such any alarm on the engine would be hard if not impossible to hear from the cockpit when operating at anything above idle speed.
Since I already have a wiring harness ran from the engine it wouldn't be difficult to just add one additional wire next to the harness and wire tie them together. It would be simple to install in the lazerette under the port side aft seat where it is easy to get to, and would be easy enough to hear going off since it would be directly under you.
Do you have some examples you can share, as I have never seen this. Every one ive ever seen had the tube coming off the top of the powerhead.
Thanks, I didn't see that info on their website. 15mA is a negligible draw, especially if you only power it when the ignition is on / engine is running, plus I would assume the single sensor probably draws even less.
I think that is going to be my solution. I'm adding that to my mid to late summer projects list.
All the OB's I've used the pisser was connected to the supply to the water jacket.
and they were good indicators of an impeller problem
and I've had more than a few OB's. 3.5nissan, 6johnson, 9.5 evenrude, 9.8merd, 15evenrude, 200merc, 235johnson.
+ I probably missed some...
water going to the head needs some pressure tube to get that high... can't imagine a stand alone hose for the pisser...
You are exactly correct, the piss tube is normally on the SUPPLY side of the water jacket, NOT on the DISCHARGE side. If there is a clog IN the water jacket (like a chunk of broken impeller vane or sand / salt buildup etc) that clogs or restricts the water flow going THROUGH the water jacket, the piss tube will never indicate the problem since it is upstream of the restriction.
On many / most engines piss tube pressure is a good indication of water pressure / flow from the pump to the engine (i.e. is it pumping or not), but is meaningless for water flow through the engine actually cooling the block.
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