P38 4.0L V8 loosing coolant but cannot see where!

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Based upon the checks that have been made and assuming that they have been carried out correctly - particularly pressure testing the system and giving the engine a good thrashing under load with the pressure testing equipment on it to check running pressures.

The first thing to do is as follows, with a cold engine, remove expansion cap, turn off the air conditioning - if fitted, turn the heater up to MAX and turn heater fans to midway position, start engine and run at idle while watching the water in the expansion bottle.

You should see the fine jet from the small pipe at the top of the radiator, where it enters the side of the expansion bottle, this can get blocked or restricted.

Water level will raise and lower in the bottle until the thermostat reaches temperature, when the level will suddenly drop.

Try this and report back with what happens
pay particular attention to any overflowing of the bottle
if you start to get lots of bubbles or glugging, stop the engine and let us know.

If possible check the temperature of the top and bottom hoses and even the radiator in different places once the engine is warm - an infra-red temp gun is ideal for this, but an oven thermometer will do if you dont have access to one.

The more information you feed back the easier it will be to help you.
 
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