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MG MGA - Temp/oil guage repair?
My temp/oil guage has had the sender cable for TEMP severed an inch and a half from the rear-
Is this sort of damage easily repairable?
And if so, can anyone please recommend an Oz repairer
Or am I better off looking for a replacement complete unit?
|Mark..I had the same problem about 2 years ago ( sensor cable broke behind gauge )and after a brief search into alternatives...I bought a replacement Smiths gauge with temp cable from LBC..about 160 us dollars I recollect. You can get them repaired apparently but was not much cheaper. New unit has worked fine ....|
|I have had several repaired here in Ringwood with no problems. The tube is filled with (I think) ether and most times they supplied new tube. They also supply a brass ferrule to connect into the cast iron head, always a source of trouble when it is removed at a later date.|
For all instrument repairs I recommend:
Ringwood Speedo Service, 693 Whitehorse Rd. Mitcham Phone: 9874 2260
They are on the boundary of Ringwood and Mitcham.
|Mark, I found the photo of the brass ferrule -- highly recommended. |
|Mark, You could also try Howard Instruments also in Melbourne! http://www.howardinstruments.com.au/|
These vapour pressure temperature gauges are not difficult to repair but there is a problem of getting hold of the fluid that goes in the brass bulb. I’ve repaired a couple of these, one in the mid 1960s and the other, an MGA one last year. When doing the first one I used diethyl ether (DEE) to go back into the bulb just because I had some lying around from the days when I mixed my own model diesel engine fuel. Those were the days when, barely out of short trousers, you could go into a chemists shop with a corked empty pint bottle and get them to fill it up with ether albeit leaving a dent in your pocket money. Last year when I called in several local chemist’s shops and asked for ether I got blank expressions with comments back like ‘never heard of it’ or ‘even if we had it we couldn’t sell it to you’!
A year ago you could buy it on Ebay but only in large quantities (gallons) costing the earth.
This got me thinking about whether there was an alternative to DEE.
I first had a look on the internet to see if Smiths had actually used DEE in the early post war period but couldn’t find anything. Then I decided to find the pressure required, using an air compressor, to give a full scale deflection of the temperature gauge: this turned out to be 100 psi which is, of course, exactly the same as for the oil pressure gauge. So Smiths had actually used identical Bourdon tubes in the construction of these two gauges.
Now I looked for a liquid that would have a vapour pressure of 100 psi at 110 deg C (230 deg F). The closest I could find was n-pentane giving 100 psi at 109 deg C and next closest were DEE at 107 deg C and ethyl mercaptan at 105 deg C. Because of the close link of vapour pressure with boiling point all three of these liquids have a boiling point of around 35 deg. C.
However, even though n-pentane is a constituent in petrol I wasn’t able to find a supplier of the stuff in small quantities at a reasonable enough price. In the end I asked an industrial chemist I knew whether he could get hold of something giving him the choice of the first two and he came up with 100 cc of DEE which is plenty because only 2 cc are required to refill the bulb.
For my two gauges both leaks had occurred near the brass bulb, one at the soldered joint and the other through a split capillary which I removed by shortening it by an inch or so.
I found the best way to insert the fluid into the brass bulb was to drill a small hole, around 1 – 1.5 mm diameter, through the tip of the bulb large enough to insert a hypodermic syringe needle and inject a couple of cc into it. Soldering over the drilled hole to seal the system is a bit tricky because you obviously can’t use a naked flame and it must be brought up to soldering temperature quickly otherwise the fluid at the bottom will boil away at 35 deg. C. I used a large soldering iron of 75 – 100 Watts and held a wet rag around the bottom of the bulb to keep the fluid cool.
You have an additional problem of getting hold of some new 1/16 inch capillary tubing but there seems to be plenty around on internet sites although when I looked last year I couldn’t find a supplier of the protective coiled steel wire that surrounds the capillary………………………………Mike
I appreciate your work on this, as I have been contemplating capillary repairs myself.
|Yes that sounds great Mike. I have a newish gauge that I bought at a boot sale with a broken capiliary, thinking one day I will get it repaired, from your description I think I will follow your example. I too know an industrial chemist. :)|
|Robert (Bob) Midget Turbo|
|I looked into repairing a capillary type thermostat a year or two ago and found nothing. Now this post and a few other sites describe the process. It doesn't sound like a difficult process for a true DIY'er. |
This info wasn't available, or at least I didn't find it 10 years ago when I needed it. My Moma rebuild had plenty of length. If the MGA factory original capillary tube is long enough and the fault is at the one of the ends or the bulb itself, then maybe you won't have to replace the tube. I found this site describing the repair:
I just found the armored wrap on eBay:
Sounds like an interesting project!
|You could use the following: He does all instrument sets for Sleeping Beauties Restorations here in Brisbane (who by the way have had two 2nd place getters at Pebble Beach Concours). He is probably the best in the Southern Hemisphere and is not overly expensive|
Otto Automotive Instruments, 07) 3277 3888
|As a will idea I was wondering if you could buy a cheap Temp gauge from a local parts store like this one which comes with a capillary tube for $22 and adapt the fitting of the capillary tube to the original gauge. May save some hassle...|
Just an idea...
I have the same memories of buying chemicals at the high street chemist for model engines at age 11- not only ether but nitromethane and amyl nitrate !
|The capillary in Chuck's Ebay ad. looks just the stuff but it's pricey. I've measured my MGA Jaeger capillary at 104" so you would need two lengths making $60 plus about $30 to the UK. The length on 'Gonzalo's' gauge is only 72" so not enough. If anyone knows of a UK supplier I'd be interested...............Mike|
|You can buy Ether by purchasing starting fluid. It doesn't need propellant, and should work fine. I would use an ice bath with dry ice, as it will really keep it cold if you have issues with the job.|
|Mike, Don't use your starting fluid as it may not be pure ether. This was the first thing I tried when I drew a blank at the chemists last year. I used our Bradex starting fluid which I assumed was pure ether with a propellant: I was wrong because the needle deflection on a boiling water test showed around 45 deg C. I could have saved myself the trouble by looking up the COSHH data sheet of Bradex on the net where it indicates that there is less than a third of DEE in it. The rest is made up of hexane, di-isopropyl ether, acetone as well as the propellant propane which disappears anyway. They may add these other materials to keep the price down.|
Hexane and the other chemicals (except propane) all have a lower vapour pressure than DEE.................. Mike
|Well thank you. I had just taken it for granted that it would be ether. I'll have to get some elsewhere.|
|FWIW, Phillips Temro "Zerostart" (standard for big diesels) is a bit better.|
DE Ether 60-65 % by weight 537mmHg @ 25C
Hexane 30-40% 45mmHg @ 25C
The CO2 should go away, so the DEE should come out around 70%.
By the notations in my old chem books, I once knew how to calculate the result, but that's gone!
Or you could probably distill it.
Might be at least functional though, with adjustment.
Can buy at:
Dear, and it may be on the DEA no go list, as the druggies have figured out how to use it.
|Fletcher R Millmore|
|A 'back of the envelope' calculation shows that a 70/30 mix of DEE and hexane would give 91 deg on the gauge at boiling water temp.|
There are many chemical suppliers that list DEE (e.g. our Abbey Chemicals gives a price of around £12 for 500 ml of DEE or pentane but the problem is getting it shipped because special hazardous chemical couriers have to be used and this increases the cost quite a lot unless you live close of course. Neither can be shipped in the normal post.
You could try contacting someone in a local aeromodelling group as they may have someone who mixes their own fuel and would sell you some ether...............Mike
This thread was discussed between 01/07/2010 and 11/07/2010
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