Heat soak/Vapour lock - advice please

[JonnyP]

I would appreciate the guidance of this super knowledgeable group.

TC2190 has always suffered somewhat from from heat soak and will not re-start when hot without a ten minute wait for things to cool a bit. I have always resisted fitting a heat shield because I prefer originality, but have grown tired of the problem, so fitted a heat shield and phenolic spacers between the carbs and inlet manifold.
Unfortunately, objectively it has made no difference. Neither better nor worse. When the engine is hot I can easily put my hand on the float bowls, choke levers, etc, etc without them feeling very hot, but the problem persists. Pulling the choke does not help at all, so all I can do is wait for things to cool a bit.
The car runs fine when it is going and does not overheat. Timing is 9 degrees BTDC and the points, rotor, and condenser were replaced only 300 miles ago with parts from the Distributor Doctor.
I have run out of ideas….. Has anybody ever encountered the same and found a fix?

[Tim Jackson]

It could be a failing ignition, perhaps the coil. I fitted an in line spark plug tester to one HT lead to check for a spark when the engine fails to start. I left this in place until sure of the result.
With regard to vapour lock, ceramic coating the exhaust manifold will help reduce the engine bay temperature. I use premium fuel in preference to standard grade, as this is likely to be less volatile according to Paul Ireland
https://ttypes.org/manchester-xpag-test ... onclusion/

[JonnyP]

Thanks Tim, I’ll try the spark plug tester, it’s a good idea. The exh manifold is ceramic coated, but that doesn’t seem to make a difference and as you suggest, I do use premium grade fuel.

[Duncan M]

The new ethanol laced gasoline (10% or whatever) will go bad quite a bit faster than real gasoline. Seems to go bad faster in warmer weather. One months is not unheard of. Not any studies on effects of bad gas on hot starts.

My TC had louvre's punched on top around 1951 and the car has never had a heat soak problem, even on very hot days. No spacers and never a heat shield. I have heard people with no louver's make the same claim.

Adjusting these carbs correctly can be a challenge. Here is an article that explains proper adjustment. Saves a lot of of headache over the hocus pocus methods. Once you have done it a few times, it can all be done by eye. This article below refers to racing car SU tuning, but I guarantee that once you get the fuel and jet heights adjusted to these settings they work for a completely stock TC or a full race one, too. Nothing is more important in the H2 than these settings you will never find in an SU instruction manual. You can make a measuring tool out of a properly sized wire with the tip bent over, if you like. Page 29. To accomplish the goal you will need to be clever. Note that .0625 is 1/16th of an inch.
https://www.namgar.com/images/uploads/C ... er30.1.pdf

[JonnyP]

Thanks Duncan, I’ll give it a try.

[stephen stierman]

I had the same problem with TC2911. As I used this car regularly and filled the tank several times a month the problem was not old petrol. It could have been caused by ethanol as that is all we have here for the most part. I had spacers under the carbs, a coated exhaust manifold and made up a little heat shield, all to no avail. Opening the bonnet of course cured it but as I always ran Brooklands screens with a folded wind screen this was a bother. I did find that pulling the choke on start up and running for a few minutes would get things going again. I was running standard needles in the carbs.

[Steve Simmons]

Ethanol definitely contributes to vapor lock. Different parts of the world, even from one state to another in the USA, have different blends with different levels of ethanol in the mix. Here in California we're lucky that nothing over 10% is currently allowed to be sold for use in normal gasoline cars, but in other parts of the country they're selling up to 30% from what I've read.

Another thing to check is your advance curve. Setting the timing at idle only tells you it's correct at idle. Check it at 3000 RPM to make sure it's advancing. The previous owner of my SA suffered terrible overheating issues and the mechanic working on it charged her a ton of money to clean the block, rod the radiator, make many adjustments and even put on an electric fan. I refused to believe his claims that this was normal, and when I purchased the car the first thing I did was investigate. I found the distributor advance mechanism was locked solid, so the car was running at about 5 degrees throughout the entire range. I rebuilt it, set the timing properly and it has never run hot since, even on very hot days.

TCs are not known to run hot. I've had mine in temperatures up to nearly 120F without any overheating issues. At those temperatures, there isn't a stock TC on the planet that won't suffer a bit of vapor lock when you try to start it again, but pulling the choke clears up the rough running quickly and opening the bonnet when you park can make all the difference. But in normal temperatures it should never be an issue. It's strange how some TCs and TDs seem to overheat no matter what while so many can drive through the desert all day and barely get warm. I do run mine a tad rich and that might help a little.

Louvers don't seem to make as much difference as we would like them to, but they definitely evacuate air. If you've ever driven a TC with top louvers and the windscreen down, you'll feel (and smell) the hot air on your face. Maybe another heater option for the Winter?

[stephen stierman]

TC2911 never overheated and it was only heat soak on fairly warm days, the car was black by the way which didn't help matters I am sure. Louvering the bonnet was something that I was definitely not going to do. Our petrol was 10% ethanol and eventually I learned to live with it and just pulled the choke as needed.

[Tim Jackson]

Vapour lock may not be the problem if “pulling the choke does not help at all”? My TC had similar symptoms, finally diagnosed as a faulty regulator cooking the coil. Paul Ireland concludes that “ethanol does not appear to make petrol more volatile”, but modern fuel is probably more volatile than it was years ago

[JonnyP]

As you say Tim, pulling the choke makes not the slightest difference. If it did I’d accept it as an idiosyncrasy that I could put up with, but at the moment I’m wary about how I use it and where I go in case chaos ensues…..
I’m waiting for the spark plug tester to arrive to explore the failing ignition possibility further and also Steve’s suggestion about advance mechanism not working, although 2190 does not overheat, no matter how hot the ambient, as long as she’s moving.

Steven, did you ever cure it on 2911?

[Steve Simmons]

If the choke doesn't make any difference, good or bad, then I would suspect the coil. They are most efficient when cold, so the hotter they get the more they suffer. When you test a coil, it should be done cold first, and then repeated when hot. Often coils that test and perform perfectly at room temperature completely fall apart when heated internally.

That said, it's odd that it will run fine but not start again until it sits. That's really more of a fuel-related symptom. Maybe the coil is getting just hotter enough when the car is parked? But it doesn't seem like it would cool off at all in just 10 minutes. Very strange.

[Tom Lange, MGT Repair]

I would very definitely follow Steve's advice about the distributor and timing. No more than 32 degrees at full advance.

My recommendation would be to send out the distributor to be rebuilt by your Distributor Dr. You will be surprised how much better the car runs afterwards.

An XPAG should not overheat on its own. Your internal cooling passages may well be diminished with rust and debris. Sadly, nothing short of removing the core plugs and flushing the engine will fix that, which is best done with the engine removed.

Tom Lange
MGT Repair

[JonnyP]

Latest update.

Tim, thanks for the suggestion of the Sparkrite tester. I fitted one to each plug this morning and started her up. Big fat orange spark at each plug, so went for a twenty five mile drive (about the distance where problems begin to occur). Stopped the engine, which of course wouldn’t restart. Checked the Sparkrites and every plug had an intermittent and very weak spark, sometimes almost non existent.
I’m delighted to finally have a lead on the problem and amazed that the car will idle as well as it does with so little power at the plugs…
Am I right in thinking that this indicates the coil is breaking down?

[Tim Jackson]

Jonny, I’m pleased to hear this cheap and simple spark plug test has identified an ignition fault, and nothing to do with fuel. My engine would stop, usually in slow/stationary traffic, and more likely on a warm/hot day. There was never any sign of engine overheating (my car is also black). The plug tester revealed no spark until waiting ten minutes or so.
In my case, the coil was failing when hot, and working again on cooling down. However, the same thing happened with several new coils over several years. I finally tracked the problem down to erratic voltage from a faulty voltage regulator, which was overheating the coils.
So yes, it sounds like your coil may well be failing, but the condenser could also be suspect. I’d replace each in turn. Let us know how you get on

[Steve Simmons]

That symptom is most likely a weak coil.

[JonnyP]

Just to close this out, I fitted a new coil today. Problem solved.

I’m frustrated that because the symptoms were those of heat soak, I just assumed that was where the issue lay and chased the wrong problem….

The Q12 I took off was dated April ‘48, so I guess nobody could say it hadn’t performed!

[Franz Tenbrock]

yes
had the same problem
some month
now i have a new car :-)

i will buy a new cap, 4 new spark plugs, a rotor, one accuspark and a coil
and put it in the back of the car
all this parts you can change in some minutes