PVC Exhaust

whats a qualified marine surveyor?
he's not coming to check for class
he's not coming to check USCG compliance
he's not coming to check EU CE compliance
sure he'll find Thailand compliance is perfect

 

Good question ---when he comes what shall I ask him.

Im not in Thailand I live there but keep my boat in Malaysia.

Again ---sigh---He is swiss not Thai

 

perfect, Malaysia has absolutely no rules at all for pleasure craft

 

I keep it in Malaysia but is not there now I am in Singapore.

 

I forgot I had a very hot hair dryer. I put the cooking thermometer in the hot air stream and the most i could get was 74 degrees. I then placed the hot air stream right at some PVC plastic piping. I honestly expected to be able to bend it.

After a good 10 minutes concentrated in one place on the edge of a pipe it became far too hot to touch. I got some pliers and I could not move it or bend it at all.

I think we just got to think of PVC in another light. Which is all the thread is about. Dinosaur theories left to wander into the future.

 

My exhaust has some plastic parts on the old 1970 eggharbor power boat.
V8 engine
Off the cast iron risers it is rubber hose about 4 feet.
The twin outputs recombine into a large bronze Y receiver with a 5 or 6 inch exit. That bronze receiver also has a water injection port.
Then a 1 foot section of rubber 5 or 6 inch diameter hose to a long large fiberglass muffler. Then another 6 inch section of rubber hose connects to a 5 foot black plastic tube. Then another rubber connector then the exhaust exit is a large diameter section of copper tube goes out the transom. On the transom of the boat I have added rubber underwater extensions to vent the exhaust underneath the surface. It has made a difference on the fumes.

So this is original to the boat from 1970. Last year one of the raw water pump impellers disintegrated. I immediately noticed the engine beginning to overheat up to about 260F. It overheats quite fast.

Shut down quick with no fire no damage. I think a good idea would be to have a temperature sensor strapped to an exhaust pipe. Wire it to break the engine ignition if it overheats to shut off the motor.

The clothes driers use these sensors to monitor the air temp. I think one would work for that?
question is where to mount it. Put it on the black plastic tube or the bronze Y ?
The clothes drier sensors are directly exposed to the hot air stream to react quickly. Our drier has 3 and they come in various temp ratings. Thing is you will have an insulating effect mounted on plastic. so perhaps better to mount on the metal riser or the metal Y. Somewhere to actually measure the exhaust temperature, not the coolant temp.

Do they make a thermal sensor to thread into a housing that can withstand hot salt water?

 

Ive used a common strap on heat sensor on the wet exhaust for years.

Now that correct sensors are widely available its worthwhile to use them. Contact your marine engine shop to see what is available.

http://www.halyard.eu.com/Products/alert_configurations.html

Halyard supplies very many components to the yacht building industry.

The LAW states that all new builds must have a sensor in the wet exhaust to warn of coolant loss.

 

But are they suitable for plastic wet exhausts?
Strap-on sensors work well on metallic pipes and ducts because metals are good heat conductors. The temperature on the hot side of the pipe wall is pretty much the same sensed on the cold side.
But plastic is a heat insulator. Thermal conductivity of PVC is 0.1-0.2 W/m°C , against 20-40 W/m°C of various steel alloys. So the temperatures on two sides of the plastic wall be pretty different. How do you resolve that problem with a strap-on sensor? By setting a much lower max. temperature for alarm activation?

 

Yup, unfortunatly my strap on is not the best solution, but 20 years ago when I installed it, it seemed a good idea.

The sensor saddles the hose clamp after the water injection jacket and is user adjustable so it will fire off at low temperture setting. Mine is set at 60 degrees.

If your building a new system, you should use a temp probe into the wet exhaust.

Im sure there are many suitable products since it is now the law.

I only know the Halyard system because I installed it on a new generator exhaust sytem.

Check with your local engine shop for advice .

 

if your looking for a cheap idea, then drill a hole in the rubber hose
Screw in an automotive engine heat overheat sensor unit. Back it up with a bronze female pipe joiner that you cut off of a fitting. And seal it with permatex silicone gasket maker.

Or weld a threaded bronze or copper fitting into the metal part of the exhaust stream and screw in this sensor.

Typically these will have brass and copper on the end in the exhaust stream. So likely they will last for a while.

When the cooling water goes away, the exhaust air temp will rapidly rise and set the sender unit to conduct current. This means you have to wire it in with a relay to trip the engine ignition off. A standard 40 amp Bosch 12v SPDT relay will work. Wire a buzzer into this circuit and or a overheat light so you know what happened when the engine quits.

 

It will work, but Im not happy with drilling a hole thru rubber.

If the hose is wire reinforced you will have a hard time fabricating a tight joint. Also exhaust hose expands..pulsates.. when pressurized. Any perforation will shorten its working life. Better to seat the sensor into metal by extending the water injection jacket to accept the sensor.

 

yes, the metal attachment point is a better idea.

Exhaust pressure is very low, it wont leak if you do it like I said.

The Permatex gasket maker is excellent for sealing exhaust. Use the copper high heat formula. Let it set for hours before running to fully harden.
It will seal a rubber hose. I have used it to seal exhaust manifolds to heads.

You can buy a solid copper threaded female pipe fitting normally used for copper water pipes to use for the nut on the backside of a rubber hose or for welding on a threaded fitment for the sensor. Use a torch with silver brazing type idea for attachment to a cast iron part or you can use brazing rod.

Make sure the sensor part of the system is exposed to the exhaust stream, not shrouded by a pipe.

 

This is a typical aftermarket marine sensor for penetrating rubber hose.

http://siliconmarine.com/ExhaustTempManual.pdf

 

http://www.ebay.com/itm/Airtex-Engi...e:Buick|Year:1965&hash=item5aec3323a5&vxp=mtr

I used to have a 62 buick, so I know this one would work. It has 2 connectors on top.
One is on to ground with engine cold.
One is on to ground with engine hot.
So you have to ground thru the body of the sensor.

Some sensors you would get would be thermistors made for gauges which you dont want.

Anyone know of another sensor normally made for a car that is just an overheat light sensor?
We also had a 75 Chevy that had an overheat light and no gauge.
http://www.ebay.com/itm/GENERAL-MOT...evrolet|Year:1975&hash=item3cc8fc8f23&vxp=mtr

I imagine some simple on - off sensors would be 2 wire which would make this easier to connect.

 

What is better is a raw water failure alarm. It will alert you of no water which will inevitably result in over heat but you know about it before it even gets hot.

This is what I appear to have as my alarm would not go off on a cold start because the water strainer cap was not perfectly seated and causing the smallest reduction in flow.

A simple car type heat sensor is cheap they have one wire and the on off temps are stamped on the body.

It will need to be on a metalic surface.