The factory cooling system on the AE86 GTS (SR5 is similar)
works very well. It has more than enough cooling capacity for
the standard engine, and will work reliably for the life of the
car with a minimum of maintenance.



The water pump is belt driven from the crankshaft and has the
radiator cooling fan mounted on the front of the pulley. The fan
has a viscous coupling controlled with a bimetallic element. This
allows the fan to "freewheel" when it is cold, but progressively
engages to spin the fan as it heats up. This is a well proven
system, and works fine for any normal use.

Water circulates through the engine as shown in the diagram.
From the pump into the block, up into the head, and then out
to the radiator top hose. Most of the water exits from the front
of the head, but some takes an alternative route via an outlet
at the back of the head. On some versions of the 4AGE, this
outlet contains the cold start injector time switch and the ECU
water temp sensor. It also supplies water for the heater and
the thermostatic idle-up valve under the throttlebody.

The engine water thermostat is located in the return neck from
the radiator, and controls temperature by restricting the amount
of water flowing through the radiator. When the engine is cold,
the thermostat is closed. To promote fast warmup and avoid
hotspots forming inside the engine, a bypass system allows water
to circulate inside the engine until the thermostat opens.

The water pump has a telltale weep hole underneath, and when
the pump is worn out, water will start to weep from this hole
and dribble down the frnt of the engine. When you see that,
start planning a water pump replacement.

Always use an anti-freeze/corrosion inhibitor in the cooling
system. Mix it with clean water (preferably distilled) according
to the manufacturers instructions, and replace it once a year.

Cheers... jondee86

Thanks For the rundown. I, for one, didn't know about the weep hole. The top of my oil pan, below the crankshaft, is nice and clean. It is the only clean spot. Now I know to buy and replace the water pump again.

Think I'll do the crankshaft seal while I'm there. The timing belt and tensioner are fairly new and in good working order.

Weep hole usually leaves a rusty track. You might be losing enough
oil out of the crank seal to wash that spot clean ?

Cheers... jondee86

Hmm..., I've been checking the oil level after i did an oil change plus new filter. Doesn't seem like a lot is getting out. All the same I need to verify. When the engine is running I don't see any oil or coolant from that area around the crank.

^Mine leaks from the weep hole, but I haven't actually seen it leak while the engine was running, or even hot. Sometimes I'll notice a dribble of coolant on the lip of the oil pump casting from the driver side after the car has been parked overnight. Also, after switching to Toyota red coolant it's MUCH easier to see compared to the green stuff. Fwiw I lose a very negligible amount of coolant; I changed the fluid around 1 year ago and haven't had to top off the overflow. The pump is definitely on it's way out though.