I have about 3000 miles on this engine that I rebuilt, after a catastrophic failure at the race track. The head was not rebuilt and has about 10,000 miles on it since the rebuild. I noticed my radiator was swollen last week, and that it was wet around the top tank seam. Now, looking at photos from when I blew the engine, I see that the swelling actually happened when I blew the engine last year. It was a major head gasket failure and three shattered pistons from detonation. So we know the radiator took a beating when the engine blew. It is getting replaced next week. However, I am thinking that I still may have a head gasket leak, or a crack in a cooling jacket of the head because...

I started my Z from cold, with the radiator cap off, and the water level rose steadily and overflowed the neck in about 2 minutes of idling. Is that a normal expansion rate or does that seem too quick? I saw no bubbles, just rising coolant.

I am going to try to get a cooling system pressure tester this week. I want this sorted before I install the new radiator of course.

Opinions?

Edited March 27, 201213 yr by cygnusx1

I have noticed the rising coolant when the system has not been fully bled. I would think that if you were getting cylinder pressure the car would be running poorly or you would see lots of turbulence in the radiator -all of the time. The last time I changed coolant, I used a new funnel from Lisle (Lisle funnel 24610). It will allow you to add coolant, watch the coolant bubble and bleed out the air, and get a full radiator the first time, which was Real Nice. You can get one on Amazon for $23.00

That expansion rate doesn't seem way out of line to me. If you have access to a sniffer you could put it in the radiator and look for HC's. An A/C leak detector works too.

I hope it's normal. I will have the car back together this week so I'll pick up a radiator tester loaner from local auto parts. I haven't seen oil and water mixing anywhere, which is a good sign.

I've had that happen to me, in the same way, waiting for bubbles that never came. Ran the engine for 20,000 miles afterward, no internal gasket problems, although it did weep when cold at the back of the head. 1976 280Z. I've drained and refilled the radiator and engine a few times for different reasons, also with a different, more solid engine (no leaks at all) and never had the air entrapment with overheating that the 240Zs apparently had. I just fill up the radiator, put the cap on, run the engine then check it after it cools down. It's never very low.

I have a steep driveway so I usually park it nose up, with the cap off after I fill it up. A proper overflow system should keep the air out, and keep it topped off all the time anyhow.