end of long drive symptoms

[IanIrving]

I've just returned from an almost 2200 mile drive through France and Spain. Other than a terndancy to overheat in the high temperatures in Spain the car behalved impecably however towards the end of the drive three symptoms became apparent. A flat spot when acelerating at low revs, say from 1500-2000 rpm, a backfire on high speed overrun ie when letting off the accelerator at high speed and the tendancy to overheat more easily than ever before. I checked points gap, removed the plugs, checked gaps etc, all good around 26 thou, but noticed that all the plugs are very very light grey. Engine has done about 10,000 miles since complete rebuild two years ago which included carbs and runs like a dream lots of power and almost no oil use, about 2 pints on the trip total. Car is BJ8 phase II. Do the symptoms described look like it's running too lean?

Ian

 

[Jeepster]

I would say it does sound like its running too lean. I would always prefer my engines to run too rich rather than too lean as it is less damaging to the engine.

Try a re tune.

 

[Randy Forbes]

All the symptoms indicate that it's a little on the lean side. I would not go too rich, as any unburnt fuel (raw gasoline) will contribute to "bore washing" resulting in increased cylinder bore wear and the dilution of the oil (increasing the possibility of bearing wash out too).

You can get away with going a little bit either way of the correct mixture, but ideally, you'd be running it spot-on.

 

[Johnny]

Ian, had similar backfiring problem. Check the timing with a light, it might of "jumped" timing. It does sound like you're running a little lean also. Another common mistake is not topping off the dampers in the SU's with a light weight oil.

 

[nevets]

What does "jumped" timing mean?

 

[Patrick67BJ8]

All the symptoms indicate that it's a little on the lean side. I would not go too rich, as any unburnt fuel (raw gasoline) will contribute to "bore washing" resulting in increased cylinder bore wear and the dilution of the oil (increasing the possibility of bearing wash out too).

You can get away with going a little bit either way of the correct mixture, but ideally, you'd be running it spot-on.

Are you still using the "special" gauges for correct fuel mixture?

 

[EV2239]

If it is ticking over okay I'd check that the Carburettor butterflies are both shut and shutting at tick over. A slight difference between the two will cause hesitation when picking up from low speeds.

Old Brit cars are always a pain in hot weather, it's as though the manufacturers never tested them. I'd put a 75 degree thermostat in the car for hot climates as a precaution.

The timing won't slip, but the points might close up.

Resistive plug leads go high with age, so measure after they've been really hot.

Always have a spare rotor arm because they fail first.

Ash

 

[IanIrving]

Thanks for the advice so far, I'm going to check mixture tomorrow, I'm interested to know what is the "special tool" refered to? I had been thinking of a lower temp thermostat. I only use the car in summer and am likely to be spending more time in the south of France or Spain where it does get very hot. I'll also check timing though I would have thought I'd have lost power if the timing were out. I did check points gap, it's ok at 14thou but maybe I should take them out ans clean them or change them incase theres a high spot on one side or the other.

Thanks again for the ideas.

Ian

 

[tahoe healey]

Once the thermostat is open, it makes no difference how hot it gets. It only promotes proper start up temperature as to when coolant flows into the radiator. I have heard for decades that people choose to use lower temperature thermostats or none at all.

 

[Patrick67BJ8]

Once the thermostat is open, it makes no difference how hot it gets. It only promotes proper start up temperature as to when coolant flows into the radiator. I have heard for decades that people choose to use lower temperature thermostats or none at all.

"non-at-all" is not good unless you have some restriction or the water will flow to fast through the radiator.

 

[John Turney]

Once the thermostat is open, it makes no difference how hot it gets. It only promotes proper start up temperature as to when coolant flows into the radiator. I have heard for decades that people choose to use lower temperature thermostats or none at all.

"non-at-all" is not good unless you have some restriction or the water will flow to fast through the radiator.

But it would also flow faster through the engine.

 

[Keoke]

Just keep the radiator clean and uprated if feasible and the correct thermostat installed and you will not have any problems.
When the flow rate of the water gets too high you pick up less heat from the engine and dissapate less heat at the radiator.-Fwiw Keoke

 

[EV2239]

Most Brit manufacturers recommended lower temperature opening thermostats for hot climates or even seasons. My Bentley for instance suggests 73 degrees C for summer and hot climates and 78 C for the UK.

Engines are more efficient at the higher temperatures, but older ones are precious and a bit of extra safety margin is no bad thing IMO.

Ash

 

[Patrick67BJ8]

Once the thermostat is open, it makes no difference how hot it gets. It only promotes proper start up temperature as to when coolant flows into the radiator. I have heard for decades that people choose to use lower temperature thermostats or none at all.

"non-at-all" is not good unless you have some restriction or the water will flow to fast through the radiator.

But it would also flow faster through the engine.

...and through the radiator faster too. NASCAR engines a restrictor plate instead of a thermostat. The engine builder I taled to told me that you must slow down the water flow through the radiator or it won't cool enough.

 

[Healeysince59]

Increasing the flow rate through the radiator will improve cooling performance up to the point where cavitation and/or foaming occurs. That is what NASCAR is avoiding with restrictor plates. They are also running at full power all the time so they don't need a thermostat to maintain optimum operating temperature. Here is an excellent write up:

https://www.arrowheadradiator.com/14_rule...automobiles.htm

Here is an even better write up if you want a lot of detail and have a lot of time:

https://mgaguru.com/mgtech/cooling/cool_200a.htm

Marv J

 

[bob hughes]

Yup
definitely running lean at light grey, should be nut brown.

For the record - mine are black due to the high carbon foot print that burning oil brings



Bob

 

[IanIrving]

Thanks again all, I reset the mixture, it was too lean. I also changed the points. The flat spot has now gone and after a 30 mile or so drive yesterday, plugs are now pale brown so that looks all good. I've ordered a colourtune plug and a timing light. When they arrive I'll check again paticularly the timing because I think it might be a little advanced cos it's tending to diesel on shut off. I'll update once checked.

Thanks again

Ian

 

[bob hughes]

Pale Brown -

Could go a tad richer - looking for a Hazel nut colour,

but clearly you are getting there.



Bob

 

[Johnny]

Doesn't make sense to circulate super hot water. You must have a thermostat to slow the circulation to give the water in the radiator a chance to cool.

 

[Dave Richards]

I naively thought this was thread on the symptoms the driver had after a long drive!

My wife and I just finished a round trip to the British Invasion in Stowe. About a 500 mile round trip through some of the most beautiful Adirondack and Vermont mountain country including a ferry ride across Lake Champlain. The car ran flawlessly, the driver did not. Aside from tremendous back soreness, the return trip resulted in a cramped accelerator foot that left me in agony the next day after our return. Just part of driving a 40 plus year old car and a 50 plus year old body.