AO Platinum Member
Join Date: Feb 2002
Location: The land that Time forgot
Re: Whats correct 'normal' temp.
The thermostat should ALWAYS be at or near 90C regardless of what you're doing (apart from if you just started the engine at the North Pole).
The thermostat closes when the temperature is less than this, so that the water in the block can't go through the radiator and so warms up to 90C as soon as possible.
Then, it opens (in small amounts), so that the hot water can go through the radiator and be cooled. The hotter the water becomes, the more the thermostat opens, until it's on maximum open.
As you drive along (at 80 on the motorway) the thermostat is constantly opening and closing in small amounts to keep the temp' as close to 90 as it can.
If you temp' stays down at 50 then it's clear that the thermostat is stuck open (so the water can't be heated). Your fan coming on at 92-3C shows the cooling fan works okay, so no bother there. Just change the 'stat. You'll notice the car uses a touch less petrol (the mixture is richer when the engine is colder) and warms up quicker in the winter too.
Thermostat's fail every 3-4 years. They have components made of brass (they expand to open the 'stat and contract to close it) but brass contains copper and that corrodes in time and causes the movement to stick. Keeping your antifreeze nice and concentarted helps, as antifreeze contains corrosion inhibitors. If your coolant is just water then your stat will fail sooner (and probably the engine will have rusty water in it).
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