Cylinder deposit

[Jonty]

yes, durring reving. Especially with a coolant bottle such as that. Your return is right at the water line, so its going to create a Venturi effect and churn up water and air. The original coolant bottles return at the top, as do many stainless ones, they will also make bubbles, but way less. Now as for how long the bubbles are hanging around (like bubbles in soapy water), perhaps you have some sort of surfactant mixed into your coolant.

Thanks for that. I have still lost a bit of coolant recently and there was a lot of air in the rad. I’ve attached a video of it. Would be fascinated to know if yours does the same.

https://youtube.com/shorts/aNyNAK_1hPo?feature=share

[Parzival]

Mine does not lose coolant. However Mine and all other local deloreans in my area will churn up bubbles when revving the engine.
Are you over heating? How much coolant are you losing?

[Jonty]

Mine does not lose coolant. However Mine and all other local deloreans in my area will churn up bubbles when revving the engine.
Are you over heating? How much coolant are you losing?

No I’ve never over heated. I noticed the other day the expansion tank was near empty so topped it up. Seems to be holding now but keeping an eye on it.

[Parzival]

here is what I think you should do. I think you should hook a leak down tester to the cylinder with the deposit in it, and while you are pushing pressurized air into that cylinder look in the coolant bottle and see if the level rises. Or better yet put the pressure checker on there and pump it to like 5psi, then put the leak down tester on there, if you see a rise on the coolant pressure tester while using the leak down tester at all you know for sure the head gasket is leaking. This is a much better test than the blue fluid as it will reveal a small leak where the fluid tester may not. Of you can put a balloon over the neck of the coolant bottle and then use the leak down tester, if the balloon inflates at all while using the leak down tester you have a head gasket leak. You can do all this with the car cold, and then put the spark plug back in and drive it until its warm and do it again while it's at temp incase the leak is only occurring cold, or once warm. (if you find the leak while cold, don't bother trying again hot, just get ready for the rebuild)