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How To:- Change the Thermostat / Bleed the Cooling System

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MR2 MK1 Cooling System

Just to dispel a myth that is continually brought up about the coolant, Nowhere in the BGB or in any of the Toyota manuals that I have, does it mention Forlife or that not using it will have dire consequences for your engine (and bring death and destruction to you).

This is a direct quote from the BGB aka the Toyota Repair Manual. " Use a good brand of ethylene-glycol base coolant mixed according to the manufacturer's directions" The Toyota 4A-GE engine manual repeats this statement and goes on to add "we recommend a mixture of more than 50% coolant to water but not in excess of 70%"

Toyota recommends changing the coolant every 30,000 miles or 36 months.

The coolant system capacity is 12.4 litres (including the heater) Which means that

  • 50% = 6 litres of undiluted coolant and the rest water
  • 70% = 9 litres of undiluted coolant and the rest water

I normally go for about 8 litres of undiluted coolant, which equals approx 65%.

Draining the system / Changing the Thermostat

  • Raise the car slightly at the back (ramps/axle stands) or park on a slope nose down..
  • Set the heater control to hot.
  • Drain the engine and radiator

The BGB recommends draining the rest of the system by the drain plugs on the metal pipes below the car. I've found this to be a bit risky as the plugs are usually corroded. I found it much easier just to remove the hoses from the radiator and let it drain there.

  • If changing the thermostat, remove the 2 bolts,  the water inlet and the thermostat from the water inlet housing.

Now is a good time to flush out the cooling system using a garden hose . Normal water flow is from the engine to the radiator down the pipe on the drivers side, through the radiator and back to the engine on the passengers side, reverse and forward flush until the water runs clear.
If you want to flush your heater matrix ( a good idea)  remove the 2 small pipes in the engine compartment 1 at the thermostat housing and 1 on the side of the engine block above the gearbox.


Normal flow for the heater is from the side of the block , to the heater and back to the thermostat housing, reverse flush and forward flush until the water runs clear

  •  Refit the water inlet with the new thermostat and gasket



Refilling / Bleeding the Cooling System


There are  3 bleed points on  car. (see the drawing above)

  • 1 at the water inlet on the thermostat housing
  • 1 at the right-hand side of the radiator
  • 1 at the heater valve

There should be 2 service hoses coiled up next to the heater bleed point. (if not use 2 lengths of plastic tubing about 3ft long)


  • Fit 1 to the heater bleed point and suspend the other end from the washer hose
  • Fit 1 to the radiator bleed point and suspend the other end from the bonnet stay ( make sure both ends are higher than the water filler )
  • Make sure the heater control is set to hot (fully open)



  • Open each bleed valve 3-4 turns
  • Fill the reservoir bottle to the bottom line (minimum)



  • Start pouring the coolant into the water filler
  • When the coolant begins to come out of the water inlet bleed valve, close the valve


  • Continue pouring coolant ( slowly) into the filler until it is full
  • Check that both the suspended tubes have coolant in them and the level is the same as the coolant filler ( it helps to give both the radiator hoses a gentle squeeze to help get rid of any air)
  • Close both the bleed valves at the front.
  • Fit the filler cap and turn to the  first click



  • Run the engine at a fast idle for about 3mins then switch off.
  • Check the coolant level at the filler neck and top it up if it has dropped, then repeat the previous 2 steps
  • Repeat until the level stays constant
  • Completely tighten the filler cap



  • Top the reservoir bottle up to the top line.


Take the car for a short run until it has fully warmed up and watch the temperature gauge, it should be steady just below halfway.

You may need to repeat the bleeding process a couple of times (if your unlucky)

If all is Ok then your done. This is more or less the Toyota way , with a couple of additions that have worked every time for me.

Jimi Lawson 


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