Where does cooling system vent overpressurization?

[andrewwynn]

When my reservoir failed on N55 it failed right where the vent would overflow so of course i first replaced the cap. On the E53s both off ours failed with the seam up the back.

On E53 the first sign of leak was no cabin heat. (we had basic dash no coolant level light).

Did you have overheat when the serpentine belt bit it?


–awr–

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[Clavurion]

That picture was also on my retina, but was not at hand at that point.

[paramax55]

Originally Posted by andrewwynn

When my reservoir failed on N55 it failed right where the vent would overflow so of course i first replaced the cap. On the E53s both off ours failed with the seam up the back.

On E53 the first sign of leak was no cabin heat. (we had basic dash no coolant level light).

Did you have overheat when the serpentine belt bit it?


–awr–

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I did not have an overheat, which bothers me. The gauge stayed exactly in the middle even after the upper hose exploded. It eventually did move, but long after it should have. It's entirely possible that it overheated, blew the head gasket, then started pumping pressure into the system before the needle ever started to move. I'm going to make certain long before this thing goes any distance.

[paramax55]

I could not get anything to move in the cap. I even ordered a new cap just in case mine is stuck, but it's the same way. Does the relief move with internal springs and seals?

[andrewwynn]

Internal. Not like old timer spring with disk.

The needle on e53 is nearly pointless it shows about a 40° C swing in temp as "perfectly fine". No indication it's about to overheat until it does.

Usually the overheating will be caused by the reservoir or hose blowing.

If you shut down within minutes of a venting situation you likely caused no damage.

The problem is when the coolant how's the sensor will be often be dry no longer measuring anything useful just the steam blowing past it.

The idiot gauge that's pretending to be a thermometer is really a 3 position idiot light.

1: ice cold
2: warm, normal or hot
3: way too hot should have shut down five minutes ago

I drove my poor car for four months in open loop when my thermostat failed due to the moronic design.


–awr–

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[paramax55]

It has gone 7 miles so far and it's doing what it's supoosed to. I put the head gasket tester on it and the fluid stayed blue until the antifreeze expanded and contaminated it.

When the belt broke, it took 1-2 minutes from the time that I noticed the battery light until the hose exploded. It probably took another 30 seconds for me to work my way to the right hand side of the interstate and get into the emergency lane. The gauge still read normal when I shut it down and started coasting. I had to start it 2-3 more times to run up to coasting speed again (30 mph or so) so I could make it into a parking lot - a few seconds each time. The gauge did reach the 3/4 mark at the end. The longest trips in this thing are going to be 3 1/2 miles for a while before I trust it.

When I lost the water pump in my e30, it took another two weeks before the head gasket gave up. And that car has a turbo. A couple of days later, I had a new head gasket on it and it's still going. I love the simplicity and reliability of the M20.

[andrewwynn]

Coolant shouldn't expand enough to come out the top of reservoir. Even though you have to vent the pressure if the engine is warm. At operating temp there will be some normal pressure but if your coolant is concentrated enough it shouldn't boil at atmospheric pressure.

Did you dilute with distilled water when replacing the hose?

You should be able to run the car up to operating temp (use hidden menu or an IR thermometer on the upper hose to measure the thing on the dashboard is pointless).

Once warmed up, shut down and let it cool just a few minutes then slowly open the reservoir to vent pressure.

Then you use the tester and only vapor should come out no fluid. If fluid comes out suggests either the head gasket is blown or the coolant is diluted and boiling.


–awr–

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[paramax55]

The system is overfilled and the tester only holds 2CCs. When I took the tester off, it's not like it was regurgitating and nothing is leaking after the latest test drive. It was just splashing around in the reservoir. I'm not condemning this head gasket yet but I'm not trusting it either. I need to drain off some coolant and keep testing.

[andrewwynn]

Yeah you need some air space above the tester. If you had a coolant pressure tester (basically a pump with a cap that goes on the reservoir with a pressure gauge), you could measure the pressure when operating temp.


–awr–

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[80stech]

The "block check" test works well AFAIK but we have had some people say it didn't work for them and I don't know if something has changed to make it not as reliable as it used to be back in the day. Anyway follow the instructions and treat it like a smoke test, If it shows a problem there is a problem, but if doesn't then doesn't mean there isn't one.

You might try driving the car for a while through a number of heat/cool cycles without taking the cap off so that the gases might have a chance to accumulate a bit more before testing. Then follow the instructions. Get the tester on quick after removing the cap. I remember we even had someone from the company that makes the test kit chime in on a thread in support of it!