overheating exhaust nightmare.

[turnbuttonboy]

Having fitted a new silencer and checked that the back pressure was correct we had a run down the Douglas today. Punching the tide a 1500 rpm, which is flat out on our set up, we found the feel of the boat was much improved and she generally ran much happier. She also smelt better! Having bought a probe type thermometer, which we installed under the exhaust bandage where the fire had broken our previously (presumably the hottest spot), we found that the new silencer produced a temperature on the outside of the exhaust itself of 580 degrees C. This is still higher than we expected but is this figure excessive for a fully loaded 5LW?

 

Once we dismantled the old system we could see that the exhaust pipe was fabricated in two and a half inch pipe, which is a fraction (one eigth of an inch!) smaller than the minimum recommended by Gardner but that the bends were in 3" with the smaller pipe welded in. Could this minimal difference in bore be responsible for the above heat and would it be worth tearing it all out and going straight through in 3"? Or is that an awful lot of work for a few degrees reduction?

 

Thanks for all the previous advise - if all is well then maybe we will get some proper Guinness this summer after all!

 

Giles

[Yoda]

The reduction in bore size from that given ie 3 inches will cause some problem, you can go up to 3.5 or 4 inches. More of a problem is the 90 degree bends in the system. These can cause high back pressure, large reductions in velocity and pulse reflections that stifle the whole exhaust system. All sharp bends should be well away from the headers.

[LEO]

Hi,

 

Pleased to hear that things are sorted out in part, how long do you think you will be running the engine at full revs? and what is the tempertature like at say 75% of full revs.

 

On a smaller scale. I have 2 right angled bends on the system for my 2LW which are relatively close to the engine which cause no apparent problems, even running against a strong current on the Thames last year.

 

Bet a 5LW running at 'full chat' sounds impressive. www.Gardner-Enthusiast.com may be able to help.

 

ATB

 

ALBI

[LEO]

Hi,

Sorry I see you have posted on GE, shall watch replies with interest.

ALBI

[smileypete]

I spent today installing the new silencer - the engine now runs as quietly as she did before and produces about four inches of back pressure at 1800 revs (100 more than we used to get). Four inches is a little higher than we hoped but we are still running the exhaust through the two and a half inch pipe the boatbuilder fitted which, according to Gardner, is one eigth on an inch undersize and the three 90 degree bends don't help. We will test the pressure under load this weekend when we run up to Preston again, which will be fun if all goes well. If we do get back pressure in excess of 10" then we will have to rip out all the exhaust pipe and rebuild in 3" but this would be a pain to do and we hope that all will be well as is.

 

The 90^o bends won't help, can you test back pressure before and after?

 

cheers,

Pete.

[Dutch Bargee Man]

Hi Giles

Sorry to hear about your problems regrarding your exhaust system, i too just recently have the same problems, ironically they sound identical .

My problem was the boat builder did put the pipe in at 2.5" and it seemed i had three different diametre of pipe cobbled together to try and make a full one????.

Perhap!s they where just lying around the workshop on that day,

What happend to my engine after this shoody effort was put together was it blew the injectors due to a volume of back pressure in my Gardner so that they ceased to atomise correctly so i had lot!s of unburnt fuel, which in turn led to high volumes of carbon soot build up!s "Mucky Stuff indeed" . I was the only boater in the pub looking like a panda with orange lips until i realised what was giong on and got Walsh!s out . people kept thinking i had simply come in fancy dress.

I know have replaced my total exhaust system with the correct "4 the recommended size and belive if or not it work!s like a new one,"Giles my engine sound totally different now like the sound of an irish throabred rather than flactulance from sombody! behind.

"Phew who would trust boat builders???????.