MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Hot Coil

Help!I have a problem that I would like to sort out before we drive up to New Jersey next week.

I have a 1980 MGB with a Luminition electronic ignition in place of the original Lucas setup. This has been installed since just before our trip to MG '96, so perhaps 12,000 miles. The coil (Lucas DLB 102) runs hot - so hot that after a half hour drive, you can't touch it for more than a fraction of a second without burning yourself. I've had other coils on during the last few years - the original coil, a spurt coil, and now this new original coil, and they all ran hot. Has anyone else experienced such a problem, and what was the cause? Surely this can't be good for the longevity of the coil.

Joe Mercer

Joe, The coils on my two B's run hot, 68 GT and 74 Rd. One has a Lucas sport coil and the other has a standard Lucas coil. I have Crane XR 700 electronic in both cars. I have a non contact thermometer and have measured as much as 170 degrees on the lower end of the coil on a hot day after a long run. I had a Bosch blue coil on the 74 and it also ran hot. It's caused by the current consumed to make a high voltage ignition spark each time a cylinder is fired. I think what you are seeing is normal. FWIW, Clifton
Clifton Gordon

Thanks for the feedback. I suspect that my coil is at least the 170 degrees you have measured. I felt the coil on a friend's 1980 B after we had both taken a trip. His was warm (not hot) to the touch. He still has the original lucas electronic ignition.
Joe Mercer

DLB102 is a 6v coil, and with after-market ignition systems is probably running at 12v instead of 6v. My 12v unballasted and 6v ballasted coils with conventional points run warm, but not so hot I can't keep my hand on them unless I leave the ignition on without the engine running. Like you, I think it cannot be good for the coil. If you can beg, borrow or steal a 12v coil I'd see what that was like.
Paul Hunt

I have a Crane/Allison solid state spark box that will just about fire under water so it has a good hot spark (I run .040 spark plug gap) and my coil (a Bosch blue coil) only gets warm, not hot.
Sound like something is astray to me but I don't know what. Be sure you have a good high quality coil designed for high output ignition systems, and maybe carry a spare.
Wayne Hardy

Joe. The Lumenition system can be set up to operate with either a 6V coil or a 12V coil, but the appropriate voltage input for the coil must be used. For several years, we ran my daughter's 77B with a Lumenition and the stock coil with no problems and no over heating. This was the way the car had been set up when we purchased it. When I got an extra Sports Coil, I looked at the installation instructions and found how to wire it over to 12V input for the Sports Coil. That also worked well and the coil does not overheat. Thus, what the others are telling you, that you are suppling a 12V input to a 6V coil, is the most probable cause of your problem.

A secondary possible cause would be that the coil hold down clamp has been overtightened and has compressed the body of the coil, causing internal shorting. I have seen this one time. Both possiblities are easy to check. Les
Les Bengtson

I thought I measured around 170 degrees but I didn't record the information and my memory may not be correct. I did do some measurements today after a run in our 90+ temperature with the 74 roadster. After the run I measured 135 to 139 degrees. The coil was too hot for my fingers. The entire engine bay gets hot under these conditions. The distributor was around 155 degrees, carb piston chambers around 118 degrees, Cylinder head around 175 degrees. Inlet to oil cooler 130 degrees outlet 108 degrees. Exhaust manifold was around 260 degrees which is low, it is coated inside and out. My concrete driveway read 105 degrees. I didn't measure and blacktop roads but I suspect they would have read around 130-135 degrees. With everything in the engine hot it appears the coil is only getting a little hotter than the surrounding area. BTW, I have the Crane box in front of the radiator support and it was about 105 degrees. FWIW, Clifton
Clifton Gordon

I discovered the hot coil phenomenon myself a while back and changed my blue coil out for another 12v coil. They both were hot after a run but not so much that I left any skin behind when I touchd them. Bob Thompson suggested that I check the amperage draw and I found that both were the same and correct. Just a normal situation that I never noticed before.
David
David

This thread was discussed between 17/06/2004 and 18/06/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.