| Author | Message | ||
| james dean boggs (Jd_boggs)
Registered Member Username: Jd_boggs Post Number: 144 Registered: 11-2004 Posted From: 71.121.51.91 Rating: N/A |
I have replaced the electric oil pressure gage with a mechanical type. I had to buy a 50 ft spaghetti tube and connect it from rear to front. But I get no pressure even after letting the tube hang on the other end waiting for the oil to seep out the end. No oil coming out! Do I need to use 1/4 inch line instead of 1/8 inch? Anybody have this problem before? Thanks. | ||
| Cullen Newsom (Cullennewsom)
Registered Member Username: Cullennewsom Post Number: 118 Registered: 2-2009 Posted From: 98.201.161.214  Rating: N/A |
It's called hydraulic friction loss or something like that. It's not unlike electrical resistance. If the pipe isn't clogged it should eventually "charge up" but may take more minutes than you like, making it fairly useless as an instrument. Yes, a bigger pipe, or an electrical sender. An industrial 4-20mA type unit if you want to eliminate all of the error caused by a long wire. | ||
| Paul Lawry (Dreamscape)
Registered Member Username: Dreamscape Post Number: 537 Registered: 5-2007 Posted From: 64.40.215.135  Rating: N/A |
That's why on most buses they go electrical, too long of a run with too much resistance. | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 972 Registered: 11-2005 Posted From: 208.54.200.22  Rating: N/A |
jd, I've never heard of an oil pressure line that long?? Try using a plain pump type oil can and pump into the spaghetti line until oil flows out the end. The idea is to get the air out so the pressure can be transferred. I've done this numerous times with aircraft oil press lines but they weren't quite so long. Yours should work but will take a bit longer to fill with oil. If you mean 1/8" OD that is the correct size. If it is ID it is too large. There is no oil flow, only oil "push" so it doesn't need to be large. The smaller the better in case it springs a leak!! | ||
| Cullen Newsom (Cullennewsom)
Registered Member Username: Cullennewsom Post Number: 119 Registered: 2-2009 Posted From: 98.201.161.214 Rating: |
More fun for you. http://www.engineeringtoolbox.com/reynolds-number-d_237.html | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 742 Registered: 8-2006 Posted From: 74.33.54.207 Rating: N/A |
James, it will work with 1/4 inch make sure it is filled with oil before connecting both ends. the way I did was pump oil till the gauge showed some pressure then connected it to the oil supply port. FWIW my turbo boost gauge will not work with 1/8 in only 1/4 inch. good luck | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1568 Registered: 10-2003 Posted From: 71.58.110.9  Rating: N/A |
just curious as to why you replaced an electrical gage with a mechanical one. Low pressure at idle? If that long line develops a leak over the miles, you could have quite a mess from it till you discover it. There are many accurate electrical units. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 743 Registered: 8-2006 Posted From: 74.33.54.207 Rating: N/A |
I use his method to check and calibrate the electric gauges at different rpms beats walking from the back to the front fwiw | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 245 Registered: 1-2009 Posted From: 24.129.232.232  Rating: N/A |
Isn't the issue of hydraulic frictional loss less of a concern in a "stactic presssure" aplication such as this (as opposed to a kinetic applications such as turning a hydrualic motor or frequent flow in a cylinder application that is in frequent motion of extend/retract ? ...oh the extents we must endure in the absence of a willingness to take on a willing apprentice , hey luv-r-bus ! | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 975 Registered: 11-2005 Posted From: 208.54.200.15 Rating: N/A |
If you use a larger line you will have a larger loss of oil in case of a gage line leak. That is the reason to use as small as possible. Oil under high pressure can leak very fast. There can't be much friction loss if there is no movement?? I, too, wondered why you would want to change to a mechanical gage with its leak possibilities? | ||
| james dean boggs (Jd_boggs)
Registered Member Username: Jd_boggs Post Number: 145 Registered: 11-2004 Posted From: 71.121.51.91 Rating: N/A |
I replaced the gage because my old bus had at least 4 different gage brands and models. Some were dim other were way too bright etc. So I set out make them all the same brand and model VDO Series 1. Even the fuel tank gage did not work properly. Now everything works fine. I replaced the 1/8" OD lines with 1/4" OD line and in 30 seconds or so the line began to bleed out the oil and thus expel the trapped air. That finished I snugged it up and now get instant response to throttle. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 892 Registered: 10-2006 Posted From: 76.195.234.106  Rating: N/A |
Accuracy of electric stuff , esp to auto mass market standards is to me questionable. I have a box full of VDO if you want to play. The SW mechanicals seem among the best , but it might be hard to order and install a temperature gauge with a 300 inch lead. For folks that are willing , the Murphy Gage folks will make mechanical anything you want , at a very nominal cost. Best of all the Murphy Gagues can be had with user adjustable alarm set points. Temp high? Fluid Low? It tells you! FF | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 976 Registered: 11-2005 Posted From: 208.54.200.47 Rating: N/A |
jd, It filled with oil much sooner simply because it was a much bigger hole. Now that you have gone with the 1/4" line be sure you have a restrictor fitting of some sort at the engine end to minimize any possible leaks in the gage line. This is standard practice with oil gage lines, even 1/8" ones. A lot of oil can flow through a 1/4" line in a hurry. This restrictor won't affect the pressure readings. We are talking pressure here, not oil flow. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 896 Registered: 10-2006 Posted From: 76.195.234.106 Rating: |
Attempting to bleed the line will be far simpler after the oil is thin and 200F , rather than on start up. FF |
