It’s a mk10 auto and I wanted to test the compressions . The starter solenoid is mounted on the starter , so couldn’t operate it manually , so I took out all the plugs , switched on the ignition ( couldn’t do it any other way ) and pressed the starter . Then I couldn’t stop it , even by turning the ignition off ! Had to disconnect the battery , what’s going on ???
Stuck solenoid. Plus twenty
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Is that a fxxxxd solenoid ? I need a new one then ?
Most likely. Plus twenty
I would not be at all surprised if the solenoid can be taken apart and cleaned.
If not, you have nothing to lose by spraying cleaner and lubricant into it, if possible
likely it just stuck from an accumulation of grit
tehy are available as new reproductions I believe
Certainly worth a try: it’s been long enough since Ive seen one, I’ve forgotten their serviceability.
Thanks guys , I’ll see what I can do .
This is the starter in 4.2 L Mark X.
What happens inside is there are two copper contact bolt heads and a copper disc on a steel shaft that is pulled toward them by magnetic force and makes the connection.
The contacts get dirty from many arcings with many startings, and there is reduced good contact area, until it is so small that the arc is enough to melt the copper contacts and weld them together.
A good hit with a hammer might pop them loose.
But it’s just going to happen again.
I believe you are completely correct, my error, I was thinking for some reason it maybe a 3.8 with remote solenoid, (but seems they dont have a remote solenoid either).
think I read a post recently that I did not know, showing availability of a solenoid overhaul kit,
(but I could be wrong again!), you may search on the topic as the author was @peterjb
I restored a 1938 Lucas solenoid, but in that case there was no acceptable alternative if I was to keep it original.
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So it is the solenoid which is at fault , and not the starter . So a new solenoid , if available , would solve the problem ?
The solenoid is just a heavy duty switch. If you short the terminals ( thus connecting the starter directly to the battery) you will know if it’s the solenoid or starter. Just make sure the car is in neutral.
I don’t know that they are available for the type built in to the starter, which I recall you said you had.
Some cars such as my early Jaguars have them separate, mounted on the firewall or inner fender.
I remember one time back in my college days I was jumpering the fender mounted solenoid on some girl’s non-starting '71 Ford with a pair of keys, the only metal I had on me. It turned over but didn’t fire, so I realized the ignition was off and told her to turn the key on. Then I jumpered it again and the thing started up with a roar and nearly ran me over. Luckily she was at the wheel and had the presence of mind to hit the brake. She had left the car in Drive, which turned out to be the reason it wouldn’t start on the key.
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Women! 
We’re all very glad she didn’t run over you! 
Cheers!
Ps. That starter is just like the one I had on my 1966 4.2L E-type 2+2 and I have very similar looking spare from a Ser 1 XJ6. You can service the solenoid on top of the starter, or have the whole unit reconditioned by a professional company.
Just found out that SNG do a reconditioned complete exchange unit . . . . . on backorder , so watch this space !
Thanks once again guys . Oh , one other thing , it’s a bit difficult to start from cold , and the engine surges all the time the Thermo is operational , when it reaches temperature and it cuts out , it’s fine . Any ideas ?
Do you know of any shops that rebuild generators and starters?
Doing so is a doddle for a good shop.
The thermo starting carb has a mixture adjustment, it’s the little hex sleeve nut where the needle goes through the center. It limits how far the needle can go down in operation. Turn it counter clockwise, i.e. screwing it out or up, to raise the needle and enrich the starting mixture.
One thing I’ve loved about JL over the past 20 years is the foreign dialogue. So please help me out…What the Hell is a doodle from a hood shop?
Doddle (not doodle, just so you don’t mix them up) is another way of saying “easy”. So in the case it’s an easy repair for any competent shop.
Chris
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^^What Chris said! Plus 20 other sayings!