Think my coil overheats, but new coil: same prob

[CajunTR3]

I'm posting about a 1960 TR3a. It was my dad's car in college, then my first car, then my brother's. My little bro kind of ran it ragged, then parked it for seven years until I started working on it last summer. Finally got it drivable last weeks, and it's looking rough but running great, except for one major problem:

Whenever I drive it for more than 20-30 mins, it keeps running, but won't start again after I park it for a few mins. (It did stall out once, but I wasn't driving, so I'm not sure it wasn't the driver's fault) I thought maybe it was an overheating coil, as I had fixed a similar problem with a new coil back in the 90s, but changing the coil didn't fix the problem. My thinking was that the hot coil was throwing enough of a spark to keep it running, but not enough to start. The coil I took out was a nice Bosch blue coil that was about 15 years old, but only had maybe 10k miles on it. I replaced it with a crappy autozone valuecraft unit, but I figured since it was only $25 and available now, it would at least work long enough to confirm the problem and work while I ordered a better one.

I'm still suspicious of the coil situation. I felt it a couple of days ago after it had been sitting for over two hours and it was still uncomfortably hot to the touch. The temp gauge in the dash seems to work fine and stays at 185F when warm, a little more on hot days, which is pretty typical for the car as I recall.

I'm no TR wizard, but I'm fairly to somewhat competent, and I'm stumped. I'm hoping to gather a little advice before spending more money on yet another coil or on other stabs in the dark. Anybody have an idea of what it could be or how to find out?

 

[tomgt6]

Can you drive the car as long as you want. Or lets say 5 miles at any speed and it doesn't stall out? Have you checked the float bowls and know it is getting gas?

Why I ask is because I had an issue like this and found that my relined gas tank was done wrong and was clogging the lines. It would run, I could drive it for a couple miles and then it would stall and not restart for a day. Then it would start all over again.

 

[poolboy]

Kinda sounds like fuel percolation in the carbs' float bowls.
A lot of that when it gets hot outside. I see it was 98 in Baton Rouge today; I bet it hasn't exactly been cool over in Lafayette

 

[TomMull]

Here's a couple more thoughts. First, You need to determine if it's a fuel or electrical problem. You can check the coil with a spare spark plug grounded against the engine. Should see a nice blue white spark. You can also check it right at the HT lead on the coil but a bit harder to do. A good spark will jump a quarter inch or more at the coil and again with a blue white color.
Secondly, make sure the coil is correct. At the time, some cars used an external resistor or resistor wire. Using an external resistor type coil without the resistor might cause your symptoms. Finally, your hot coil may be normal, particularly in Louisiana summers. If you've got good spark, don't worry about the heat,
Good luck with your very nice car.
Tom

 

[Mickey Richaud]

Welcome to the party, Coozan! (Cousin, for those lacking a Cajun accent) Shreveport/New Orleans transplant to Tennessee here.

As you can tell, this is a great place for assistance and chat about all things British.

Oh yeah - we like pictures!


Mickey

 

[TR3driver]

Your Autozone coil requires a ballast resistor, which the TR3 did not have originally. You need to either get the proper (internally ballasted) coil, or add a ballast resistor (which might be available at AZ, try asking for the ballast resistor for a 1970 Plymouth Valiant).

However, I agree with poolboy, it sounds more like percolation to me. A very common problem in the US today, as our fuel is designed for use with sealed fuel injection systems rather than our old carburetor systems. With the carbs hanging over the exhaust manifold as they do, the heat from the manifold will literally boil the fuel in the jets after a hot shutdown.

The problem is pervasive enough that Joe Alexander has started making carburetor heat shields for the more popular Triumphs:

https://the-vintage-racer.com//index.php?main_page=product_info&cPath=3&products_id=32

 

[Guest]

Where y'at cuz !!!!


Here's a quick easy check if you're by yourself, after you try and it doesn't start, spray carb or brake cleaner down one carb throat and see if it will try to start. If it does, it's a fuel problem, if not, ignition. I don't know if your 3 has a carb port you could spray it in like my 6, but that's even simpler.

 

[Guest]

Your Autozone coil requires a ballast resistor, which the TR3 did not have originally.

Depends on which one they gave him. All the big boxes sell both in a "universal" form and most systems will list both, even though one isn't correct.

The good news is he has a better chance of getting the right coil than finding someone behind the counter who knows the difference.

 

[TR3driver]

Depends on which one they gave him. All the big boxes sell both in a "universal" form

Things must have changed then, because when I went looking a few years back, none of the discount chains stocked a points-type coil that didn't require a ballast. Some stores said they could order me one, but none of them had it on the shelf.

 

[CajunTR3]

@TR3driver:
I'll check when I get home, but I think it's a 12-volt coil. The TR3 never had a ballast resistor ignition as far as I know and it was specified by the computer for this model. Plus it looks nearly identical to the Bosch blue coil that I had been using. I know neither of these things is proof positive, but I'd never even heard of this issue until a couple of days ago in my online research. I'm definitely going to confirm that the autozone coil is non-ballasted before I run it today, because I've read that and unballasted 8v coil can basically melt the distributor.

@kellysguy:
The system at Autozone only had noe coil listed when I saw the screen, though it's possible it was only listing what was in stock.

 

[CajunTR3]

I've been able to drive it as far as I want, it hasn't stalled out on me once. That said, I've been hesitant to take it to far for fear of getting stranded. The time it did stall out I was in the passenger seat. It was running fine under power, but when he clutched to coast to a red light it died at idle. He started it again with the clutch, but it died as soon as he stopped revving, did the same again, then he didn't have enough momentum to try again and couldn't get it with the starter.

 

[CajunTR3]

@tr3driver
@kellysguy
@TomMull
@poolboy

One thing I forgot to mention about why I'm thinking ignition is that when it wouldn't start I've tried a couple of time to use starting fluid to get it to catch with no effect. Seemes to me if it was a fuel thing this would at least make it catch until it burned up the ether.

Also, don't know if this is relevant, but it's not entirely an off/on problem. Sometimes when I've driven it a bit, but not too much, it will start weak. What I mean is I'll be cranking it and when I stop to give it a rest, I'll find it's actually running, just too weak/slow to hear over the starter noise, and I can rev it up to life with the pedal. Once I rev it up to a good roar, it will idle strong and normal.

 

[TR3driver]

Today's starting fluid seems worthless to me; even carb cleaner works better as a starting aid. But neither one will work if the mixture is too rich or the plugs are wet.

Pretty much all the symptoms you describe are things I've seen with my own TR3, when the underhood temperatures are high. I frequently have to pull the choke knob out a little, to activate the fast idle cam (without pulling the jets down) to keep it idling.

That includes the weak starts; although my exhaust is loud enough that it's rarely hard to hear it firing over the noise of the starter.

I'm not really trying to argue that it is not ignition; only that I don't think you've ruled out fuel either. But I'd still try a coil and maybe some "known good" points & condenser, next.

 

[swift6]

Don't trust the computer at face value. The Autozone computer once told the kid behind the counter, who showed me the screen, that my TR6 only required 4 spark plugs. When I told the Autozone kid that I still needed two more spark plugs as a TR6 had a six cylinder engine, he told me that my car had the wrong engine in it. Followed up with the "Computer is never wrong."

 

[CajunTR3]

I'm certainly not trusting that autozone's computers are a peerless source of info, but I've looked at the packaging from the coil which says that ballast-type coils are marked with "Use external resistor" which this one wasn't. Anyway, since the coil didn't fix it, I'm planning to reinstall the Bosch unit which gave good service and is a better quality part I think. Today I drove it maybe 5 mins to the corner store and had the weak start problem already when I came out to go home, which doesn't seem nearly enough time for the coil to overheat, but it was a bit of idling at the light, which cooks the engine compartment without any air moving. So I'm leaning back to thinking maybe it's a fuel vaporization problem, especially since the only thing that seemed to help the weak start was to pump the gas pedal like a bellows. But the choke doesn't help when it won't start at all. Not really sure how to address the possible "hot carbs" issue though, maybe rig up a temporary heat shield similar to what tr3driver showed above, but that seems like it would only help radiant heat direct from the manifold. Didn't really have time to get my hands dirty today, but I'm off again Sunday, so I'll swap the coil back/check spark etc then.

ALSO: I have a diagnostic gimmick I was thinking of. If it is a vapor lock in the bowls, then I was thinking I would run it plenty long enough to know I'll have trouble restarting, but before trying it I'd fill two plastic bowls with ice water and tie them up under the carbs to chill the bowls for a couple of minutes. If it starts up then like it does first thing in th morning, then I'll know that's the problem. Or am I missing something? Would chilling just the bowls be enough?

 

[Guest]

Ohm it, IIRC, 3ohms is internal and 1.5 is external.

I worked in parts in a past life forever. The computer is mostly wrong. It's a sales catalog written by a programmer and by NO means is Gospel. I use to catch mistakes in the written books all the time and call the manufacture on it.

I think most systems now will only list what is available to the box, not what it requires. I prefer paper anyway as they seem to be more accurate. Triad was just for speed but I always used the book for accuracy.

Towards the end I hardly used either.

A ~real~ counterman hardly ever did. I hope that doesn't sound arrogant but I used to be pretty good.

Sometimes I could have a guy's parts waiting on the counter for them by the time they got to me from just a quick glance from across the parking lot.


They'd walk up and start to say what they needed and I would cut them off with the price and push the box towards them. It took me ten times longer to sell it cause they couldn't believe that was the part they needed, but sure was fun though. It would be a lot more difficult to do that today.


I love the guys who thought the catalogs would tell them ~everything~ about their car.

"I need you to look up what size bolts and wrench I need for my bumper."

Sure glad I don't do it for a living anymore but I do sometimes jump behind a counter at a friendly store and help out.

It's a good job if you like Ramen noodles.

 

[SkinnedKnuckles]

It sounds fuel related to me. Not the classic "vapor lock" where the pump cavitates and no fuel gets to the carbs, but more likely a flooded condition after shutdown where fuel "percolates" up the jet 'cause slightly higher pressure in the float bowl forces it up, and things get too rich. If it's already too rich, starting fluid won't start anything.

Personally, I've shied away from the heat shield's. I duct "cool" air into the carb side of the engine and have not had these problems.

 

[poolboy]

I suppose percolation could occur when the engine is running and the car is moving, but what I'm familar with is percolation when the engine has been turned off and the fuel stops flowing.
Laying beneath the the carbs is the hot exhaust manifold, with no moving air the heat rises and boils the gas in the carbs.
If the engine sits long enough to cool down the problem goes away, but a 5 or 10 minute stop in hot weather... well, that's another story.
I don't see where pumping the accelerator does anything constructive when talking about a SU or ZS carb,
Holding the accelerator steady at about 1/3 down is what the TR6 Owners Manual recommends when the engine is hot.
Once the engine starts, it runs kinda ragged until fresh cooler gas makes it;s way into the carb.
Heat shield and obviously the correct ignition timing and all that goes with it, and a carb mixture to suit the timing will help the engine start-up faster, too.

 

[SkinnedKnuckles]

I don't see where pumping the accelerator does anything constructive when talking about a SU or ZS carb,

Or does anything, like you say. There's no accelerator pump so just cycles the butterfly. Depressing <span style="font-weight: bold">and holding</span> the pedal 1/3 to 1/2 when hot starting as you recomended is the way to go.

 

[AltaKnight]

It's a good job if you like Ramen noodles.

Now I'm curious, not sure we get them in Canada!

I would say that firstly the coil shouldn't be so hot that you can't touch it, something wrong there; I have the Lucas Sport Coil on my '73 TR6 and it's been flawless.

Secondly, it does sound like fuel problem; though you can get high temps from poor ignition timing and also from too lean a fuel mixture.

I would pull the plugs and have a look at them, I suspect you will find they are white on the ends indicating lean mixture, in which case you will have to play with the carb(s) mixture settings.