Temperature: Above Normal or Just Average?

Hi Paddy

Good news the car runs well!

The simple answer is no these cars are capable of idling for a long time without the temperature gauge needle rising even at 28C alone 18C.

My experience is that as you have done all the flushing etc that the most likely cause is a weak mixture at idle. One of my cars exhibited this after each MOT where the garage owner weakened it to achieve a low CO reading. Try turning the adjuster nut by 4-5 flats to richen the mixture. If that cures the problem then you need to investigate whether there is an air leak if the car now runs rich above idle.

If this doesn't resolve the issue return the carb to its earlier mixture setting and re-check the ignition timing. If this is retarded it will cause it to run hot.

Another option is that the temperature is actually within spec but the sender or gauge or its bi-metallic voltage regulator is faulty. A (digital?) thermometer would confirm.

A logical one step at the time process to find the problem. (Trapped air isn't usually an issue on the crabs but turn on the heater fully, run the engine until the thermostat opens, rev it up and check the water level in the radiator as well as the header tank - when it has cooled)

David

Although the thermostat has been changed, I would not be be sure it is working as it should. I have several examples of new thermostats being faulty.
Peter

Hi All,
It was fine for the run (about 15km each way.)  
I only noticed the temperature drift up as I was checking the rpm with a gauge back home.

I checked the spark plugs - they were indeed greyish (too lean.)
I adjusted the mixture nut about 5 turns down.  I had to turn the idle screw up a fraction to bring the RPM back up to ~550.

This morning I went for another run to the same place.
When I got back I left it idling - (YES it was in garage so I'll repeat it later on the driveway.)
The needle did move but much less - just to the end of the N symbol - so that's progress.  So thanks for that.
I do feel that the thermostat is working - in that initially with the car running the radiator is not hot and then gets quite hot.


I just checked the spark plugs - they look more like that mid- brown colour I was expecting. 

Final question - when I'm filling up a radiator do I also need to fill up the expansion tank - or is that simply for overflow?

Paddy

The radiator should be filled to the top and also the header tank to its "level" mark. I would bring the idle up to around 700 for a Mk11 engine, maybe to 750 to compensate for the modern fuel. You will also get more airflow. As long as the blades are the correct ones and the fan belt tight and the radiator clear of rubbish the airflow should be correct.

What happens when you use the carb lifting pin now, does the engine increase in speed slightly? Also if you take of the oil filler cap the rpm should rise by around 200rpm. Have you checked the PCV diaphragm?

regards

David

Hi Paddy

Yes, well worth getting the PCV now the car's running. If you have the crankcase breather and the manifold PCV input blocked off you will end up blowing the engine oil seals. The carb needle / jet is made to work with the PCV in place and you won't be able to set the correct mixture across the rpm range without it.

regards

David

Here is a description of the PCV (follow the link at the bottom of the 1st page). Without the PCV you won't get proper mixture or oiling of the valve gear.

PCV

The MGB component 1964-69 is the same as the crab. Later crabs and MGBs did away with the PCV but had a different tappet cover and oil separator which fed via a rubber pipe into a constant depression connector on later MGB and Crab carbs. The latter was more reliable as there was no rubber diaphragm to deteriorate. It is possible to convert some earlier carbs to fit a constant depression tube if they have a flat area in the casting at the appropriate place that can be drilled)- there are some descriptions on MGB forums.

Note when you fit the PCV that the tappet cover, oil separator and pipes must be clean.


David

I did run let the car idle in the carport to see if it was just the lack of airflow at the garage wall.  But it did the same thing - a bit above Normal.

I'll have another look at the timing and ratio at the weekend.
Anyway decided to take the car in at the exhaust shop ( I had a go at tightening the clamp, but it was still annoyingly loud.)  So I copied out Chris's note  for the shop, about welding the screws to avoid having to have 3 hands.)

Went early to avoid traffic.
Looks like I'll be leaving late tonight to avoid the heat...

Bit to go.pdf (47.46 KB)