AO Gold Member
Join Date: Jun 2007
Location: United Kingdom
Re: 156 temperature dial fluctuating madly
That would be water temperature. It should always be at 90°c. It will drop down to 70°ish when the thermostat opens, but climb back to (and eventually stay at, with a LITTLE fluctuation) 90°. It sounds first of all that your thermostat failed a while ago, hence the LOW temperature, except in traffic.
Hopefully, the HIGH temperature is down to something as simple as the radiator core being corroded- requiring a new radiator.
Does it cool down fairly quickly when you stop? If so, it could be the water pump. These seem to break up if they are of the old plastic type (to be replaced with a metal one). They manage to spin fast enough at low revs to pump the water, but inadequate whilst driving. Unfortunately, this would be a cambelt off job.
I've rambled now, but I hope this helps?