Running Temperature

You do not need to fit higher rated thermostats (t/stat), just need a new one.

I suspect your old t/stat. is not fully closing hence, during warm up the water jacket surrounding the cylinder is not quickly warming up due to a constant flow of coolant.

In theory, a water jacket surrounding the cylinders has no flow as a result of a closed off t/stat.  As the surrounding water warms up and reaches its optimum temperature, the t/stat will open up allowing for a fresh and cool charge of water to enter the water jacket.

The resulting charge of cool water reduces the jacket temperature and the t/stat will close again until the jacket temperature rises again to re-open the t/stat.  This action is repeated several times until the whole of the water in the cooling system warms up to a point the t/stat remains open. 

Excess heat is radiated away, controlling, a safe operating temperature for the vehicle.

Cheers,

Hello Grendle,

Some additional information to help your prognosis.

The normal coolant temperature Summer or Winter is about 85 degrees.  The needle sits on the upper part of the digit 8 on the gauge.

The temperature rise to 85 degrees should be within 20mins in Summer and about half an hour in Winter (very approximate times).
Some heater warmth should be felt as soon as the needle rises above the heavy-minimum mark on the gauge.

From start up, constantly keep checking the top radiator hose temperature by hand (taking care of the runing fan!).  With a properly working thermostat (t/stat) the top hose will remain cool to the touch for the first 20 minutes or so,then the hose will start warming up, indicating the t/stat has opened.  From that point on, the hose will just get hotter and hotter to the touch.  This heat felt at the hose should convey at the heater blower, if not, you should consider a flow problem to, or at the heater matrix, we will address this issue latter.

If the t/stat is faulty, the top hose will feel warm to the touch within about ten, fifteen minutes and take up to half an hour and longer, to become hotter and hotter.

To check the heater matrix:  Feel the hose temperature by hand, on the hose going into the bulk head. The hose from the left of the cylinder head, looking into the engine compartment.  Also, feel the heat of the hose coming out of the bulk head, on the right side of the cylinder head.  Heat going in, should be almost the same as heat coming out.  If, the heat coming out is drastically less, there is a flow problem or blocked heater matrix.

Before condemning the blocked matrix, check the heater control valve and to check, if it is allowing full flow of coolant.  The valve is located under the driver's foot well panel, by the gearbox tunnel.  Remove the small panel and this will give access to the heater matrix housing and the control valve, identified with a hose going in and a hose coming out of the body. 

Feel the hose temperature going into and coming out of the control valve, if the control valve is allowing full coolant flow, the temperatures in and out will be the same, if not the valve is not functioning properly; play around with the control valve lever, turning it hot, to cold and vise-versa. 

No temperature differential indicates a faulty valve.  This is quite common, as the temperature dial is normally set to cold throughout  the Summer; come Winter time, when, the dial is turned to warm, the rubber seal in the valve becomes bonded to its seat, not opening, and to allow coolant flow.  To avoid this, never fully shut the temperature valve to fully cold.  Back off the dial from a fully cold position, a little, this is so the rubber seal does not sit on its seat.  Some minute coolant will flow by, but that small amount of heat (barely, heat) from the heater in Summer will not be objectionable. 

So, if there is heat flowing through the hoses at the valve and there is no heat at the heater blower then it is established, you have a blocked heater matrix (big job).  Attempts can be made to chemically clean this out, but for the moment we will leave that for another time. 

Cheers,