# Vapour lock, or electrical? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [January 5, 2020, 3:38pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973 "2020-01-05T15:38:32Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [January 5, 2020, 3:38pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/1 "2020-01-05T15:38:32Z")
I posted this in another thread, but I’m starting a new thread to get your opinions. > [@What made engines stall in the 1930s?](https://boards.straightdope.com/t/what-made-engines-stall-in-the-1930s/843354/13): > > My MGB has a problem in traffic. When it’s stop-and-go, the temperature gauge creeps up. Sometimes I’ll have to turn the heater and blower on – in Summer – to keep it from overheating. After a time, the engine will start running rough and then it stalls. I’d assumed it was the ignition coil or the electronic ignition module balking in the heat. > > I wonder now, if I’m experiencing vapour lock. Though it has an electric fuel pump situated in the right-rear wheel well, the carburettors are right above the exhaust manifold. What do you think? Vapour lock, or is it the coil or electronic ignition module? ---
**Author:** ![QuickSilver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quicksilver/32/7832_2.png) [@QuickSilver](https://boards.straightdope.com/u/QuickSilver)\ **Post date:** [January 5, 2020, 3:54pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/2 "2020-01-05T15:54:50Z")
If turning on the heater helps dissipate the overheating of the engine, my inclination is to check the coolant loop, not the ignition/electrical or fuel pump systems. When was the last time you replaced the following: - thermostat - radiator - radiator fan (single or dual speed?) - did a full coolant flush? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [January 5, 2020, 4:02pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/3 "2020-01-05T16:02:53Z")
> [@QuickSilver](#): > > If turning on the heater helps dissipate the overheating of the engine, my inclination is to check the coolant loop, not the ignition/electrical or fuel pump systems. The cooling system is in great shape. Since my fist car was a '66 MGB and I lived in the Mojave Desert, the temperature gauge is under constant observation. While the '77 MGBs I had had electric cooling fans, the '66s have a pulley-driven fan. The older cars simply need airflow to keep cool. I know my thermostat works because, as I said, I watch the gauge closely. On startup, the temperature creeps up. As I drive, the temperature reaches 165ºF or even 170ºF; then the thermostat opens and the temperature immediately falls to 160ºF. The temperature will rise back to 165ºF or so if I’m driving 80 to 90 mph. The only time it gets so hot I need to turn on the heater is when it’s idling in traffic on a hot day, and that’s what happened with my previous '66. I’m certain it’s either VL or electrical. . ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [January 5, 2020, 4:08pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/4 "2020-01-05T16:08:03Z")
What carbs are you running on this bad boy? (Not that I would know the difference!) Does sound like that would be the first place I’d look. I don’t suspect that the coil or ignition is going to be that heat sensitive. But you could be ‘boiling the bowls’. Too bad Keith Cameron doesn’t post here. I’ve got somewhat the opposite problem on my e10. The thing just WILL NOT GET HOT! The Weber carbs stumble and fumble unless wide open, or it warms up some. But even in summer, you can run this car, and put your hand on the radiator and its barely warm. Temp gauge doesn’t even move most times. It is strictly mechanical, and tests perfect in a pot of boiling water on the stove. It boggles the mind. How can an engine not get hot? Heater? I wish! ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [January 5, 2020, 4:16pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/5 "2020-01-05T16:16:26Z")
> [@Gatopescado](#): > > What carbs are you running on this bad boy? (Not that I would know the difference!) Does sound like that would be the first place I’d look. [Dual SUs](https://s127.photobucket.com/user/1966_MGB/media/DSCN0166.jpg.html?sort=3&o=2). If you look at the bottom of the photo, you can see that the coil is mounted on a plate that is bolted to the engine block. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [January 5, 2020, 4:33pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/6 "2020-01-05T16:33:32Z")
I suspected SUs. My uneducated guess is the carbs. I’ve just never heard of a coil getting too hot. But, hey, it English! ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [January 5, 2020, 4:59pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/7 "2020-01-05T16:59:42Z")
I should note that my first '66 did not stall in hot day/stop-and-go traffic conditions. Assuming it’s VL, [this page](https://www.mgclassics.org/single-post/2014/10/31/Vapor-Lock-The-Cause-Prevention-and-Cure) says: [quote] [ul] **Install the Carburetor-to-carburetor Fuel Line Away from the Manifold.** Using a longer line may help, also. …[/ul] [ul][li] **Insulate the Fuel Lines.** [/li][li] **Install a Heat Shield.** There are shields available for some MGs similar to the factory ones on MGBs. There is another type of shield that is actually two separate shields that mount the same way but keep the heat from getting to the float bowls. They are sold by the company that is now manufacturing SU carburetors.[/ul][/li][/quote] I think there is a heat shield installed. Maybe I need a different one? I don’t know how to insulate the fuel lines. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [January 5, 2020, 7:02pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/8 "2020-01-05T19:02:33Z")
Maybe heat-wrap the manifold? Just grasping at straws… ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [January 5, 2020, 7:03pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/9 "2020-01-05T19:03:36Z")
Maybe heat-wrap the manifold? Just grasping at straws… ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [January 5, 2020, 7:15pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/10 "2020-01-05T19:15:07Z")
Have you had a mechanic look at the car? ---
**Author:** ![Personal](https://avatars.discourse-cdn.com/v4/letter/p/b9bd4f/32.png) [@Personal](https://boards.straightdope.com/u/Personal)\ **Post date:** [January 5, 2020, 8:15pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/11 "2020-01-05T20:15:02Z")
> [@Johnny\_L.A](#): > > The cooling system is in great shape. Since my fist car was a '66 MGB and I lived in the Mojave Desert, the temperature gauge is under constant observation. While the '77 MGBs I had had electric cooling fans, the '66s have a pulley-driven fan. The older cars simply need airflow to keep cool. I know my thermostat works because, as I said, I watch the gauge closely. On startup, the temperature creeps up. As I drive, the temperature reaches 165ºF or even 170ºF; then the thermostat opens and the temperature immediately falls to 160ºF. The temperature will rise back to 165ºF or so if I’m driving 80 to 90 mph. The only time it gets so hot I need to turn on the heater is when it’s idling in traffic on a hot day, and that’s what happened with my previous '66. > > I’m certain it’s either VL or electrical. > > . Maybe I’m misreading or something, but I had a 1984 Tempo that had a problem where the cooling fan wasn’t kicking on. The thermostat worked fine, but the cooling fan wasn’t getting the message. The only way to cool the radiator was to drive to let it air cool. In stop and go traffic the temperature would redline. My old man installed a line directly from the cooling fan to a switch he installed in the glove box, so whenever it got too hot, I’d just flip on the switch, and the cooling fan would engage. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [January 5, 2020, 8:18pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/12 "2020-01-05T20:18:49Z")
> [@carnivorousplant](#): > > have you had a mechanic look at the car? _Blasphemy!_ 😃 ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [January 5, 2020, 8:31pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/13 "2020-01-05T20:31:18Z")
> [@Personal](#): > > Maybe I’m misreading or something, but I had a 1984 Tempo that had a problem where the cooling fan wasn’t kicking on. There is no cooling fan to ‘kick on’. The fan is turning when the engine is turning. The fan is attached to a pulley, with a belt that turns it and the generator from the crankshaft pulley. [Pics](https://kgcengineering.co.uk/blog/quick-job-guide-fitting-adjusting-the-fan-belt/). [Mine 1](https://s127.photobucket.com/user/1966_MGB/media/DSCN0139.jpg.html?sort=3&o=18); [Mine 2](https://s127.photobucket.com/user/1966_MGB/media/DSCN0138.jpg.html?sort=3&o=19). At least you can see the fan pulley on those; I didn’t think to take a picture of the fan itself. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [January 5, 2020, 8:31pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/14 "2020-01-05T20:31:50Z")
> [@Johnny\_L.A](#): > > [Dual SUs](https://s127.photobucket.com/user/1966_MGB/media/DSCN0166.jpg.html?sort=3&o=2). > > If you look at the bottom of the photo, you can see that the coil is mounted on a plate that is bolted to the engine block. That is a nice looking engine bay. When you have this issue, have you immediately looked at the carbs for frosting? I used to have a similar problem with an old VW bug where the Venturi Effect, I think it is called, would cause the carburetor to freeze up under certain conditions. ---
**Author:** ![Personal](https://avatars.discourse-cdn.com/v4/letter/p/b9bd4f/32.png) [@Personal](https://boards.straightdope.com/u/Personal)\ **Post date:** [January 5, 2020, 9:04pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/15 "2020-01-05T21:04:38Z")
> [@Johnny\_L.A](#): > > There is no cooling fan to ‘kick on’. The fan is turning when the engine is turning. The fan is attached to a pulley, with a belt that turns it and the generator from the crankshaft pulley. [Pics](https://kgcengineering.co.uk/blog/quick-job-guide-fitting-adjusting-the-fan-belt/). [Mine 1](https://s127.photobucket.com/user/1966_MGB/media/DSCN0139.jpg.html?sort=3&o=18); [Mine 2](https://s127.photobucket.com/user/1966_MGB/media/DSCN0138.jpg.html?sort=3&o=19). At least you can see the fan pulley on those; I didn’t think to take a picture of the fan itself. That makes sense. I was pretty sure that there was something I wasn’t understanding. I thought you were concerned with the 77. 🙂 ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [January 5, 2020, 9:10pm UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/16 "2020-01-05T21:10:41Z")
> [@Personal](#): > > I thought you were concerned with the 77. 🙂 I sold the '77s back in the '80s. 😉 ---
**Author:** ![carnut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnut/32/3531_2.png) [@carnut](https://boards.straightdope.com/u/carnut)\ **Post date:** [January 6, 2020, 1:40am UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/17 "2020-01-06T01:40:49Z")
Is it possible that the fuel is evaporating and flooding the motor? If the car is sitting in traffic, fuel might be evaporating from the float bowls. I don’t really know MGB engines but I do recall a discussion on the matter a few years ago when hanging out with enthusiasts. Alternatively, I recall that Lucas alternator brushes jam and can put a rude stop to your driving. ---
**Author:** ![Annoyed](https://avatars.discourse-cdn.com/v4/letter/a/f04885/32.png) [@Annoyed](https://boards.straightdope.com/u/Annoyed)\ **Post date:** [January 6, 2020, 7:45am UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/18 "2020-01-06T07:45:44Z")
> [@Johnny\_L.A](#): > > The cooling system is in great shape. Since my fist car was a '66 MGB and I lived in the Mojave Desert, the temperature gauge is under constant observation. While the '77 MGBs I had had electric cooling fans, the '66s have a pulley-driven fan. The older cars simply need airflow to keep cool. I know my thermostat works because, as I said, I watch the gauge closely. On startup, the temperature creeps up. As I drive, the temperature reaches 165ºF or even 170ºF; then the thermostat opens and the temperature immediately falls to 160ºF. The temperature will rise back to 165ºF or so if I’m driving 80 to 90 mph. The only time it gets so hot I need to turn on the heater is when it’s idling in traffic on a hot day, and that’s what happened with my previous '66. > > I’m certain it’s either VL or electrical. > > . If the car stays cool while driving and getting airflow across the radiator but runs hot when idling then it’s clear as day that there is an airflow issue or coolant flow issue. Clearly a mechanical problem not ignition or electrical. It sputters because the engine is too hot and it’s not tuned to run at engine temps like that. ---
**Author:** ![Jeff\_Lichtman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jeff_lichtman/32/1531_2.png) [@Jeff\_Lichtman](https://boards.straightdope.com/u/Jeff_Lichtman)\ **Post date:** [January 6, 2020, 8:27am UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/19 "2020-01-06T08:27:24Z")
How about the water pump? ---
**Author:** ![Isamu](https://avatars.discourse-cdn.com/v4/letter/i/7c8e57/32.png) [@Isamu](https://boards.straightdope.com/u/Isamu)\ **Post date:** [January 7, 2020, 3:46am UTC](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973/20 "2020-01-07T03:46:31Z")
Could be the fuel pump, is that working? Some of the old designs had rubber parts that would stick when they got hot. [Next page](https://boards.straightdope.com/t/vapour-lock-or-electrical/845973.md?page=2)