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MG MGB Technical - overheats in traffic

78 mgb ran great til latelt. runs well until you hit traffic then overheats and really runs poor wants to quit. mechanic flushed rad. changed thermostat. made sure fans were okay,choke was off repaired that. still has anti smog on car.stromberg carbs. any thoughts. thanks les
l.f. frank

What do you mean by 'overheating'?

If it's not steaming or losing coolant then it's not overheating as such, the needle going up on the temp gauge between the blue and red sections is 'normal' depending on conditions. However if there has been a change in behaviour recently then you are right to investigate.

Running hotter than it should is generally down to either the engine producing more heat than it should be, or the cooling system not being able to get rid of as much as it should be, and of course possibly both. But the first thing is to check the gauge isn't over-reading with other methods of measuring the temperature when the gauge shows hotter than you are used to.

I assume you have an electric gauge, these (and the fuel gauge) will read high if the stabiliser is not doing it's job, although that would read higher under all conditions, not just when you are stopped in traffic.

Generating too much heat can be down to incorrect carb and/or ignition operation (timing has a big effect on heat), or other problems resulting in the production of heat rather than forward motion.

Not dissipating enough can be down to restrictions in coolant flow anywhere in the engine or radiator, thermostat not fully opening, pump vane damage, blockages in the air passages through the radiator, cooling fans running slower than they should, and so on. The first thing to do there is when it is running hot scan the surface of the radiator looking for cool spots, and also compare radiator inlet to outlet when running normally and when 'hot'.
paulh4

One presumes you have checked the operation of the electric fan. Also bear in mind, in traffic you are pulling in hot air from the cars in front, so rad cooling will be affected.
Allan Reeling

Are you absolutely sure the fans come on?

And do you constantly have to top off the coolant?
Steven Rechter

I had much of the same heat issue with my 79 especially since moving from Adks.,NY to Flori-duh. One thing I did to aleviate heat was to remove the rubber gasketing surrounding the rear of the hood where it meets the cowl. This allowed some of the trapped heat to escape and the carburetor to get a cooler airflow.


Cheers

Gary
79 MGB
gary hansen

Gary, That's a dodge used by V8 owners. The under bonnet temperature on mine can sauna your face and remove facial hair!!
Allan Reeling

The alcohol in U.S. fuel makes the car very sensitive to under hood heat. The Stromberg, which has the bowl on the bottom, is sitting right above the exhaust manifold and catalyst (if your car still has one).

I carry a bottle of water that I can pour on the carburetor bowls when the fuel starts to boil. Setting the idle slightly higher for summer driving helps too (unless the red light is exceptionally long).

MGs were not designed to run on gasoline that is mixed with alcohol.
Glenn Mallory

I have similar issues and have been looking at potential causes and cures, this video is interesting although I don’t think their solution would be suitable for a B. I’d already thought about bleeding a small amount fuel back to the tank to help cool it but I don’t think my poor old SU would be happy.

https://youtu.be/cadNfSNi_Oc
R.A Davis

I've often toyed with the idea of installing a small cooling fan for the SU's. Has anyone done this?
Allan Reeling

"I've often toyed with the idea of installing a small cooling fan for the SU's. Has anyone done this? "

Well, those MG chaps at Abingdon did it, for North America MGCs. Might be some ideas on how to - or whether worth the bother - from MGC owners etc.
J N Gibson

Should be called 'confused of Cincinnati' or wherever they are. 'Vapour lock' in the title, he describes flooding, but shows vaporisation, which are three different things. He describes hot start problems, and rough running at idle, which again are two different things.

'Vapour lock' in terms of a lock preventing fuel flow just can't happen with our systems. Vaporisation can happen, but all that happens is that the float valve stays open and fuel continues to flow until the float rises and shuts it off. For vaporisation to result in fuel starvation it would have to happen at the rate of between one and two pints per minute, which is ridiculous.

Fuel return may well have worked for them, but the original pump is mechanical, which is on the engine, so has a long suction path back to the tank. That lowers the pressure, which increases the chance of boiling. Our electric pumps at the tank end are pressurising the line, which reduces the chance of vaporisation.

What CAN happen on our cars is fuel expansion at switch-off, which floods into the intake, causing a rich mixture for hot starts. But given the millions of cars with out fuel systems, the decades they have been in use, and many thousands of them in daily use in desert states, if anyone here is having a problem there is a defect that should be fixed. But that can't happen with the engine running as there shouldn't be any fuel flowing into the float chambers until any excess from expansion has been used up. Unless the float valves are faulty.

You could use fuel circulation, but it would need a different pump capable of running continuously, and you would need a 3psi pressure valve in the return to maintain the correct pressure at the carbs. I've been using my V8 regularly in this hot weather and have had no problems with it, including stop-start and crawling on the M6 a couple of weeks ago in the middle of the day. I've measured the V8 engine compartment in town traffic in a previous hot spell at 58C/140F, and not had problems, on supermarket 95. Ethanol at 10% may cause problems, but we don't have that.
paulh4

I have to say Paul, my comment about the small cooling fan is more related to our V8's and the tendency to boil the float chambers dry after switching off, with the associated stink of petrol. Like you, I haven't had a problem, even this summer!!!
Allan Reeling

Les
It's probably the ethanol fuel but----
I'm unsure which Stromberg you have and will probably cop some flak for this but
If your stromberg runs good normally and has the plastic covered bi metal strip down the side of it-approx 2"x1/2". you will find an adjusting screw just above the centre of the cover.
This bi metal strip is used to correct the idle for different temps.---It's possible that someone has tampered with this factory set adjustment
The only way to see if this is causing an issue, is to get the car in a situation(hot) where it's faulting (running rough / stalling) and have a little play with this adjusting screw -it should respond to 1/4 of a turn either way
Make sure you mark or note the starting point so as you can return to it if it's not the issue
just a thought
willy
William Revit

If it's only after switching off then I'd say just lift the bonnet - granted not so convenient when parking in a public place! If that remains shut then I'm not sure how effective a fan blowing the hottest air onto the carbs would help, unless you ducted external air in somehow.

Last week I discovered that not only does mine fume at switch-off, it drips liquid fuel. Presumably some of the vapour is condensing in the lower, cooler part of the tube.

I've no idea what form the vent on the V8 should take, it came to me with nothing, so I made a Tee for a hose from each carb, with another hanging down the driver's side of the bell-housing.


paulh4

Keeping the vents separate at least tells you which carb is over-flowing. My newly re-built V8 carbs on the Roadster experienced a petrol filled float on Monday, after only 4 days of use....................new floats!!! When a float sinks the fuel comes out as fast as the pump can shift it, this is a real flood!!!!. I put the old floats back in!!
This is only a few days after i'd recovered from the premature failure of the rubber seals on the GT's carbs!! Wondering what's next on the SU front, but I did have a 4 year old Electronic SU pump fail last year!
Maybe there's a lesson here!!!
Allan Reeling

A lesson? Oh yes :o)

Had a float sink on the V8 some years ago, and as you say it pees out as fast as the pump can go i.e. typically 2 pints per minute. I'd fused both the pump and the OD, in the engine bay, and they were close together. So I cross-connected the fuses and used the OD switch to turn the pump on for a few seconds, then off again until it started stumbling, than back on again. Got me home.

Separate vent hoses do indeed tell you which carb is leaking, but it was a moment's work back home to take them off the carbs and the wet one was the culprit. The near-side might be a bit near the exhaust, so not knowing how they were originally I opted to tee them down the off-side.
paulh4

Ever since I had my exhaust manifold ceramic coated inside and outside my carbs have run cool even in 105F weather.

I can touch the manifold shortly after a run and not get burned.

A ceramic coated manifold has also been shown to add HP.
Steven Rechter

The Revotech fan solved my problems. The Moss shroud was close, and with a later multi bladed fan probably would have worked. The one from the automatic B works well I'm told.
For some reason they put the later bonnet seal on when they sprayed it 2 years ago, the one that looks like 3 yards of sliced lengthwise garden hose. Removing that helped as well, no point shovelling air in if it cant get out.
Stan Best

This thread was discussed between 12/07/2018 and 21/07/2018

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