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Fuel & engine temperature guages


1967 MkIII

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Finally got Lucy out again for a good drive today, and of course found a couple of new niggles.

The fuel guage is under-reading, on a full tank it shows somewhere between 1/2 and 3/4 full. Any ideas before I get a new sender unit?

Can an engine run cold? The engine didn't seem to warm up, even after 2 hours blasting away on country roads, mostly in third gear. The temp guage went up to 2/3 at most and that was while waiting at traffic lights. All the rest it read completely cold. I opened the air vent into the footwell to verify a few times and the air coming in was cold, normally, as you all know it's roasting. All I've done recently is clean out the SU float chambers, tighten the choke cable (which was loose) and a new fuel filter, none of which should affect the running temperature. Any ideas what this could be??

Thanks
Steve

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A faulty voltage stabiliser could make both gauges under-read.
IF the engine is genuinely running cold (and its not just a stuck heater valve or clogged matrix making the heater cold) might suggest a stuck open thermostat.

Suggest you run the engine up from cold and see if the top radiator hose suddenly gets hot as it gets to temp or starts warming immediately.

My bet is a faulty volt stab AND a poorly working heater.

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Agreed.
Check the thermostat, it should be 88 for winter (many have the summer 82 version all year, but that should be OK and still warm up)
If unsure fit a new one, pretty cheap.
Feel the hoses, they should be at least warm/hot top to the touch.

gauges, yep the voltage stabalisers give grief sometimes. It is a small metal thing screwed to the back of the speedo, you can use a voltmeter to check the voltage at the gauges, should be about 10V, but will flicker up and down. Any lower is bad, as is constant 12V

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Thanks for your replies.

I dont have a voltmeter here but i've checked these:

Suggest you run the engine up from cold and see if the top radiator hose suddenly gets hot as it gets to temp or starts warming immediately


The top part of the rad near the thermostat starts warming up immediately till the entire radiator top gets hot. As for hoses the one between the thermostat & rad remained cold at first then warmed up, same with the hose from the bottom of the rad to the water pump. The hose between the thermostat unit and the carbs started warming immediately till it became hot. Which sounds in order to me, leaving the volt stab as the likely culprit... right?

You mention the heater matrix but I didn't turn on the heater, I just opened the vent in the footwell (ahead/over gearbox). Usually on colder days than today I get at least warm air coming in.

Cheers Steve

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2057 wrote:
Good morning all,

I've borrowed a voltmeter so will check the volt stab this evening. in the meantime, any ideas whether the thermostat is working or not based on what I found above?

thanks
Steve


A Voltmeter will give confusing results. An old style analogue meter will be ok as the needle should flick up and down. The digital meter will just get confused.  ;D

The voltage stabiliser works by opening and closing points rapidly giving an average voltage of 10V. The gauges are too slow to register that the voltage is fluctuating. This is normal!  :)

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