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Old 06-10-2020, 07:35 AM   #236
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Join Date: Sep 2009
Location: Aberdeen, Scotland

Originally Posted by 142 guy View Post
With the engine cold, remove the cap and siphon coolant out of the over flow bottle until the level is slightly above the bottom mark on the bottle (about 50 mm from bottom if the level mark is not visible). Put the cap back on, start the engine and let it come up to operating temperature. The coolant should come up to around the mid point or slightly above when the engine is up to normal temperature. Adjust by filling or siphoning as required. You don't want the level getting too high because you want to leave some extra expansion room for those hot days when you come off the highway and immediately hit a red light. You loose a lot of cooling power when the car isn't moving and the water pump has slowed down and with a really hot engine block the temperatures will go up and the coolant is going to expand. If there is not enough hot expansion room left you will get 'the burp'.

You have been driving the car a bit already so you should not have to go through the cooling system purge that is required after a coolant change. In future, any adjustments to the cooling system level should be done by adding / deleting from the over flow bottle to maintain the correct warm engine level. Do not top up from the rad cap.

Getting the coolant bottle level correct should fix your problem. If you find that you are still venting some fluid / vapour from around the top of the coolant bottle the pressure cap on the bottle may be faulty; however, my 1971 cap is original and continues to work just fine. The cap on the rad is just a cap - no pressure release mechanism. If it leaks at the rad cap then the rubber seal in the cap has failed. You can buy new caps; but, some of them have a problem. The tangs on the cap are formed incorrectly and the caps will not seal completely. If you can find some sheet rubber gasket material you can cut a new seal for your old rad cap. You may have to shim it a bit to insure a tight seal.
Jack up the front of the car as high as you can as well will help get rid of any air bubbles.
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