Land Rover Repair: Disco 1 overheating = air blockage?, radiator pressure tester, coolant level

Question
I saw your reply to another disco overheating issue.  I just did a coolant change along with a new thermostat.  My overheating may not happen even if running for 15-20 mins. When it starts overheating it will go all the way up, so I turn it off. Could I have air pockets in my coolant system? How can I check for them or get rid of them?

Thanks in advance!
James

Answer
Hi James,

It's possible that when you replaced the thermostat, air could have been trapped in the heater core.  When this happens, an air blockage can form keeping the hot coolant from reaching the heater core.

So you need to bleed that air out of your coolant system:

Caution:  severe burns and scalding can result, so be careful!

Method 1:
Make sure that the radiator is full of coolant.
Loosen the outlet hose clamp at the heater core.
Start the engine and allow it to reach normal operating temperature.
When the coolant starts to flow from the loosened outlet heater hose, tighten the clamp, and check the coolant level.
Method 2:
Loosen the outlet heater hose clamp at the heater core. Using a radiator pressure tester, pressurize the radiator. When the coolant starts to flow from the loosened heater hose, tighten the clamp.
Check the radiator for proper coolant level.
Method 3:
Install one of the aftermarket flush kit fixtures in the outlet heater hose by the heater core.
This fixture has a garden hose connection.
Open the garden hose connection cap and fill the radiator with coolant.
If there is still air at the flush connection, use the rad pressure tester to push the air out of the heater core.
When coolant flows out of the fixture, seal the garden hose opening.
Release the tester, and check for proper coolant level.

Someone once mentioned that raising the front end of a vehicle helps bring the air out.  Interesting.  Never done this but ... interesting.

You can use all the methods above.

This summer, I had to replace the thermostat on my '95.  What I did to assist in air purging was to flush the coolant after the repair.  Lastly, I removed the reservoir cap and ran the engine several minutes while watching for air bubbles.  Topped off the reservoir and replaced the cap.

Best of luck,

JohnMc