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4age 20V Cooling kit – Version 3 & 4 install guide

This guide below is for those whole wish to install a type-3 and type-4 cooling kit for a 4age 20V.

Dash temperature sensor

– From the existing engine if available. Remove the sensor used to transmit the signal to the gauge on the fascia / dash. This sensor is usually located in the original top water outlet and has 1 terminal.

– If an aftermarket gauge is used then it’s highly likely that it will have a 1/8″ NPT probe. Adapters are readily available from common auto stores, the type required is 1/8″ NPT to (M16 x 1.5).


Original engine disconnection

Undo the heater lines from off the engine, save the clamps and leave the hoses in place.


To be removed from the donor 20V engine and set aside

ECU temperature sensor and it’s copper washer – see picture below: This is located on the back of the head in the original thermostat housing. It has a long plastic top with 2 pins.

Idle speed control valve (ISCV) – HEATER KIT ONLY: Located on the intake side of the head at the back under the #4 intake runner. To remove undo the two bolts going from it into the head and then the clamp from the top hose to the end of the intake manifold. Remove with hoses and once off the hoses can easily be taken off. This valve does not require to be relocated when the new rear bypass fitted to the back of the head doesn’t have a heater outlet facing towards the intake side. However it is still suggested due to the lack of space in the original location.

Unused parts to be removed off the donor 20V engine

Complete thermostat housing + gasket + studs: Once the ECU sensor has been removed, the whole sensor housing can be removed along with the gasket and studs. To take the studs out wind on two nuts with the flanges facing each other, using twin spanners lock them against each other and then with a spanner on the bottom nut turn anti-clockwise. The whole stud should wind out.

Front water pipe / AKA “Bull horn pipe”: This curved pipe bolts to the the water outlet on the front intake side of the head and joins to the back of the water pump via a short hose and clamp. Undo the two nuts and clamp to take both off the engine. Put aside the nuts that have been removed as they are reused.


Conversion parts installation

Rear bypass plate – see picture below: This Replaces the original thermostat housing on the rear of the cylinder head.

The fittings need to be fitted into this plate. To do so thread tape or sealant is suggested both both barbs and plugs. For those with a heater compatible kit wind the barb into the rear plate to face in the direction of the heater flow control tap, or if no such valve is used then in the direction of the heater core. For those without a heater wind in both plugs as provided. This can potentially be done with the plate bolted to the head if the sockets fit. Otherwise the plate can placed in a vice with the faces protected by wood on both sides and a wrap of a rag.

Using the provided bolts and washers fit the plate to the back of the cylinder head. No gasket or sealer is required due to the O-ring seal.

Side block off plate: Replaces the original rear water outlet next to the extractor flange water outlet pipe. Using the provided bolts and gasket fit the plate to cover the open port.

New water outlet: Covers the port left open on the front of the head on the intake side after the removal of the curved transfer pipe. Slide the provided gasket and new outlet into place to then tighten with the original nuts.

Thermostat housing: This housing joins to the back of the water pump from the side and up to the top outlet via a hose upwards.

– Place the clamp provided for each over the top hose (16mm I.D) and the side exit hose (35mm I.D). Take note to face them the same way as shown in the picture at the top of this page.
– Slide the thermostat housing on so that the larger hose fits over back of the water pump and push in until all the way in. Initially only have this hose in place.
– Push on the hose from out of the temp of the thermostat housing by hand to angle it and make it fit onto the downward facing barb from the top outlet.
– Do up both clamps to face in the same direction as shown in the pictures.

Radiator hoses

The factory fitted hoses from a 4age equiped Sprinter / Corolla are able to be directly used with this kit.

Bottom hose fitment: The original hose and it’s clamp is directly fitted to the thermostat housing.

Top hose fitment: While the original top hose is used it’s extended via the 45 degree silicone hose bend as provided in the kit. Using the provided bolt clamp fit the hose to the top outlet, align the clamp as per the photo below. This can easily be tightened by using a ratchet and a long extension from the front of the engine.

Lower Hose support

Provided is a lower hose support, this is an additional mount to minimise hose and thermostat housing movement. This is designed to be bolted to an existing hole in the OEM rear wheel drive engine mount. Those using another type of mount will need a custom bracket if they wish to use this support.

To fit use the short section of silicone strap between the lower hose and the P-clamp and then with the clamp on either side of the bracket do the bolt up. See the photo below.

Idle speed control valve (ISCV) relocation

If the idle valve is to remain being used then it is rather simple to re-connect. The valve itself can be located anywhere if the hoses are extended, a common place is attached to the engine mount or throttle support with a cable tie. If an air box is no longer used a simple mini filter can be fitted on the air inlet instead of a hose.

Heater hose connection

Heater water system path: Heater systems are supplied water via the following loop below.

1 – Hot water from the back of the head (rear bypass plate)
2 – Heater flow control tap if the car uses an external type
3 – heater core in
4 – heater core out
5 – Return water into the back of the water pump or thermostat housing.

Hot water out: Hook fit the original hose and onto the rear bypass plate water outlet, or if necessary extend to reach.

Water return line connection: When the heater compatible option is selected the kit includes a connection kit in a bag and a 200mm long hose with a joiner in the end.

In their original fitment 4age 16V and 4ac engines have the water return hose is connected to the heater core, run behind the engine and fit onto the end of the steel water transfer pipe near the rear of the engine. This water hose is still used with this conversion kit however it’s extended with the provided 200mm hose and crimped barb, use the original clamp to join on to the barb. The other end of this extension hose is hooked up to the rearward facing barb out of the new thermostat housing, the hose can shortened with a trim-knife if needed.To fit this extension hose to the housing use the provided bolt clamp. For best results the clamp should be facing as seen in the photos and also where possible so that when pushed the band of the clamp touches the throttle support strap instead of the hose.

Water extension hose protection – see picture below: Also in the heater connection kit is a short split hose and some cable ties. Although not likely to be needed this is to stop a potential issue from the throttle support strap rubbing through the hose. To stop the potential issue fit the split hose over the outside of the heater extension hose and use the cable ties to hold them together and also in both directions around the throttle support.