Sunday, July 10, 2016

Coolant Added To Engine – Split Hose Issue Noticed & Resolved

The Rotax 912ULS engine has water cooled heads which require a coolant. Various coolants are approved by Rotax for the 912 ULS engine so opted to use an ethylene glycol Dex-Cool mixed 50/50 with distilled water. A concentrate was chosen as opposed to a 50/50 pre-mix so I could be sure it was diluted 50/50 with nothing but distilled water. I would suggest other builders consider the use of distilled water as well.

The top of a drinking water bottle was cut off to use as a small funnel to fit into a second water bottle that had its neck removed to be used as the measuring vessel for the 50/50 coolant dilution.
Pouring an equal amount of distilled water into the measuring vessel to mix with the Dex-Cool in the PowerAde bottle. The Dex-Cool looks good enough to drink … especially as a concentrate in a Powerade bottle. Not seen in this photo, but the bottle was marked as Dex-Cool and the Powerade label removed for safety.

After each batch of Dex-Cool was mixed 50/50 with distilled water, it was poured into the expansion tank for the radiator until it was topped off with the coolant.
Pouring the Dex-Cool and distilled water 50/50 mixture into the expansion tank on the Rotax 912 ULS engine.

When the expansion tank was full, the 18 psi pressure cap was placed on the expansion tank and as I was about to pour the remaining coolant mixture into the overflow bottle mounted on the firewall, noticed that the rubber fuel /vapor hose that connects the bottle to the expansion tank was beginning to split already. REALLY? It has only been on the bottle a few months and is already beginning to split! What gives?  When cutting the hose, a hose cutter was used … so I know it was a clean cut with smooth edges to begin with.
Photo of the Gates 3/16" ID fuel/vapor hose on the overflow bottle already beginning to split … and it has not had any service time yet. Not a good sign.

Admittedly, this hose was tough to get onto the bottle and expansion tank in the first place … and the fit is so tight, there are no hose clamps used at either end (there is no pressure here to speak of, just however many inches of water are in the overflow bottle). This got me thinking that the rubber is being stretched far too much for this application … so it got me  doing “a little FBI, 007 type investigating” to coin a phrase from a Dr. John’s song. The hose supplied is an American sized Gates 3/16" fuel/vapor hose that is being slid over 8 mm pipes that have 9 mm nipples on the end of them. The Gates 3/16" hose is actually 4.8 mm … so it is being stretched to twice its normal size. Other builders have reported this hose splitting at either the overflow bottle or the expansion tank. The DOG Aviation procurement department located some 7 mm fuel hose at a local foreign car parts supplier that is an unreinforced rubber fuel hose that has a cloth outer coating (think VW fuel line). I would prefer a reinforced rubber line, but feel this will be OK for this application for the time being. There were no specs available for the hose purchased, so I will likely switch it out later for some reinforced hose that is a known entity since the hose is relatively easily accessible. But for now, it is good enough for an engine start. Because the 7 mm hose used is only being stretched 1mm on the tubes on either end (not counting the nipple), thought it would be prudent to add band clamps to the hose as can be seen in the following photos.
Replacement 7mm rubber hose with additional band clamp on the pipe protruding from the overflow bottle.
At the expansion tank end of the hose, the hose clamp needs to be positioned so it does not go under the flange on the tank for the pressure cap … if it does, the cap will snag on the clamp because clearances here are VERY tight. The clamp in this photo needed to be moved a tiny bit to the left so the coolant pressure cap would fit on the expansion tank without snagging the clamp.

Suppose ¼" ID fuel/vapor line would be a step in the right direction if one wanted a tighter fit than the 7mm hose can offer. The ¼" hose equates to 6.3 mm which will require far less stretching than the 3/16" hose supplied, so it may resolve the issue nicely as well. Plan on contacting Van’s to see if there is a specific reason 3/16" hose was chosen for this application.