ok, so if the car is first started in the morning then the head is cracked?
 

I have a very simple question regarding my '87 300SDL. Everyone says, when the engine is cold, check the upper hose. However, should the car be running? I would think the car would have to be running for the test since it would then be that it would generate pressure that could pressurize the system.

Also, for the heck of it I popped the "bonnet" and had a look at my recently cleaned up engine bay. It seems that since I've owned it in Dec. the coolant level has never dropped. However, today it was an inch below the arrown on the reservoir. The car was hot and running, would that explain it?

Thanks
David

My coolant level is also lower when its hot and running, it goes back up once its been off/completely cools down. I believe thats normal...

I just went outside and did some testing and here's what I found...

The car has been setting about 1.5 - 2 hours and the temp needle was between the 40 and 60 mark so let's say it was at 50C. I came to this conclusion from turning the key to on and that's what it read after the car was started, bt back to the story. I popped the hood and checked the upper radiator hose, this was before I started it, and the hose was hard. So, I slowly cracked the cap on the reservoir cap and let the air get out. The hose was then very soft. I started the car and after 2 minutes of idling the hose never got hard. Is it now safe to say my head isn't cracked?

Thanks
David

You should check the hose in the morning and see if it still is hard ( holding pressure) when the car is not running........after you have shut it down for a few hours..........then check it.

How would it hold pressure overnight if there were a crack in the head? Wouldn't that let the pressure escape? And how would it build pressure if the car isn't running?

Thanks
David

You worry to much the head is fine, if it cracks you will know.

I'd worry about the head gasket more then the head.

This doesn't make sense. Water expands as it is heated, and contracts as it cools (above 4'C anyway for pure water), so when the engine is hot, the coolant should have a greater volume, which is why the pressure relief valve is fitted in the radiator cap. It lets the pressure out as the coolant heats up.
As it cools down, the coolant contracts and the other valve in the radiator cap allows air into the system.

With a cracked head, combustion pressures leak into the water jacket of the engine, pressurising the coolant system. Even after the coolant has cooled and contractsd, the pressure is still very high. This is why you check in the morning, because if you have pressure then, it cannot be due to the coolant expanding as the engine heats up.

Check the top hose with the engine OFF and COLD.

While it is possibly due to a head gasket failure, the head gasket will need replacing anyway. While you have the head off, have it tested.

Tony
The Wizard of Oz