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Hi all, took MonaViva out for a run today, first time for a few months.
Re-fuel, tyre check and a chat at the petrol station with a Cresta Owner, and then a drive of around 20 miles.

Different areas, main streets, side roads, and a small section of Motorway, but the temp gauge on the dash never once got over the rest position from starting.

No overheating, car ran lovely. When I got home all the hoses were hot, but not blistering. Rad top was hot but couldn't hold my hand on it, and no apparent coolant leaks.

So I don't feel that there is a problem, but how do I check if the sender or gauge is faulty? all other gauges are fine, and instruments all working well, including wipers and lights as I got caught in the mother of a storm!! Tested her new paintwork anyway!!

Any ideas on the gauge situation?

Fuse good and sorted the problem by taking the lead off the switch and shorting the lead to earth.
Gauge straight over to hot when ignition is on, so deducing that sender is faulty.

Next problem! getting the bleep thing out!! It seems to be grown in to the head and just won't budge.

I'm frightened in case I snap it off in the head, so I have left it be at the moment. At least I know where the problem is!

Any thoughts on how to remove it? I've just soaked it in WD40 at the moment and will try again tomorrow, 'gently'!

Maybe try a penetrating oil like Plus Gas - WD40 isn't really the right thing for it. Or if it's a tapered thread, maybe get it nice and hot and see if it releases better then.

yeah these can be a real pain- try Mike's suggestions. When you say you took the lead off the switch do you mean the connection to the sender unit?

Yes that's right Fred, the lead off the sender unit in the head.

I've given it another good soaking in penetrating oil and will try, very carefully, again in a couple of days.

Not happy with trying the heat method as it's just below the carb!!!, so I'll probably live with it for now, unless I come across another decent head to swop or one that I that I can recondition!

Don't want to remove the current head unless I have to, as the car is running so nice!

If I did find one though I would like to polish the ports and fit hardened valves and seats.
Another project dream!!!

I'm toying though with the idea of possibly fitting a sender unit in to the Thermostat housing if there is room, but that is higher than the sender unit, so might give a false reading, unless I leave the stat out?

Anyone tried anything like that?

I have made something up for Humpy where I had the same problem - Copper water pipe 15mm T piece with the smaller diam sender unit as used in the later Viva soldered into the T and a couple of 15mm pipes on each end - insert in the heater feed pipe coming off the front end of the head- you need an earth wire soldered on the T piece to complete the circuit.

On the heat thing, I was mainly thinking of you trying to undo it when the engine was hot rather than getting a welding torch onto it, but I quite understand that it is sometimes better to leave things if it looks as if it's going to cause a major issue. I've been fortunate in that regard - while the waterways on the hatch engine were very severely filled with rust and other debris, the fittings did at least come out of the manifold without any issues.



My only thought on fitting the temperature sender in the thermostat housing would be that surely the housing has nothing in it while the thermostat is closed? If that's the case, you'd just get no reading until it opens, then it would jump up very quickly.

Thanks for the tips lads.
I like the idea of the t piece in the hose Fred, think I will have a look at that.
My thoughts on fitting one in to the T/stat housing was to fit it, and leave the stat out. Water pump and rad are both newish so should be o.k.
Decisions, decisions! Will let you know how I got on.

Leaving the stat out in the summer is less of a prob as the engine gets up to working temp reasonably quickly but under winter condition it will take a long time to get to working temp which is not good for the engine.

Yes, I wondered about that as well Fred.
I use the car very little in the Winter, particularly Dec/Feb, so might not be a problem, as it's kept in a warm garage, and I seem to remember there used to be 'Winter' thermostats, with different opening temps, but that might not be the case now.

I'm drawn more to your 't' piece idea though.