Coolant expansion tank replacement

[jovani]

Due to rusty neck, new expansion tank had to be sourced. The ones I sound were priced like they are golden, both tanks and sellers. Also I wanted tank which is not on a way if working on the slave clutch cylinder, available, cheap, reliable and good looking. The latter ruled out a VW sphere. So, BMW, $18 from a running car in junk yard and choice of 6. Half the size, similar volume and same function. Pressure valve spring was replaced to open at 1.0 as the stock holds over 2.0, After finding correct hoses, installation is so ridiculously easy that I am not going to insult anyone describing it. But I will answer questions if any .

 

[lookforjoe]

Looks very good, especially the extra free space. How can it be half the size, yet similar volume though?

The obvious questions for anyone who wants to follow your example would be:

1) What model BMW (so can search online)
2) What application hoses were sourced?

 

[ianlawson]

" How can it be half the size, yet similar volume though?"
I'm with Hussein on this query!!
Maybe the BMW whiz-kids are smarter than the rest of us ordinary oiks!!

cheers, IanL - NZ

 

[kmead]

Similar, not the same.

Which means less in this case.

Ultimately there is likely more than enough coolant volume in the system, the question is more about the expansion volume. Part of this can be dealt with by how high in the system the part is mounted (ie more air to start with in the tank, thus more room to expand).

 

[Dan Sarandrea (Phila)]

Original spec for pressure cap is 11 psi (.75 bar), so even modded down to 1 bar (14.5psi), the cap may be too strong for the system. Are there lower pressure caps available for this tank?

 

[Dr.Jeff]

Without much detail we are only speculating:

Perhaps it extends down lower, giving more volume? Hard to tell, but it does not look like it. I've noticed other X's pictured on the forum with smaller than stock (aftermarket) reserve tanks. But no mention if they worked or not.

As for the hoses, the lower one appears to be two sizes of regular heater hose joined by a adapter insert.

I wonder if 14.5 psi really is too much? Has anyone experimented with that to see what the rest of the system will hold reliably? A higher system pressure will give more protection from boiling over. But only if there are no downfalls. If everything is in good condition then the hoses and radiator should handle that level fine. The head gasket already holds a lot more than that (for some of us ). Hopefully the long metal coolant tubes under the car aren't on the verge of bursting open (as both of my X's did with stick pressure - one was a heater pipe, the other the radiator pipes). Heater valves seem to be rather iffy on these cars already, so that might be an issue. Where else could a higher system pressure be a problem?

Although I am not in need of this mod for either of my cars, additional detailed info would be appreciated by the collective group.

 

[ianlawson]

Heater valves seem to be rather iffy on these cars already, so that might be an issue.

Yep, that would be MY first area of concern! I had to replace the heater valve on my 1300 X some years ago due to it dribbling when the engine was at full operational temp, even with the OE pressure cap on the header tank.
The new valve was pretty expensive, if I remember too!!

cheers, IanL - NZ

 

[jovani]

All the questions will be answered soon, I drove the car only 30 miles after installation. My heater valve is original on 1981 car and I keep an eye on it. It will be replaced with Honda valve some day, simple and reliable and available. Cheap too. As far as I remember, the original valve can be removed and the fitting bolted directly to the core, but I will check again.
The bottom hose should come with the tank, I just cut it too short from the BMW, that's the reason it is spliced at the moment. Top one is whatever I had, no specs, Sourcing, replacing and measuring the cap spring is tricky and I don't know how to explain it. Today I got digital water pressure gauge and I will T one of the heater hoses so I can watch the readings while driving and will post more info. On the 1.0 bar comment - that's what I decided to do, it is not recommendation. If you go this route, simply find the right spring. I modified 4 BMW caps, 3 with different slightly weaker springs, but have no time to test them. If something goes wrong with my set up, I will let you know.

 

[Ulix]

The tank should be out of a 5 series E39 or a 7 series E38.
Can you confim this jovani?

 

[jovani]

The tank should be out of a 5 series E39 or a 7 series E38.
Can you confim this jovani?

Sorry, I pulled it from a line of BMWs in a junk yard and never bothered to look AT the car. All I can tell you is the tank was mounted on the passenger side near the rad and the bottom hose runs across, then turns 90 towards engine and that;s where I cut it. I should reach further, but it was quite unaccessible. Tanks mounted on driver side look similar, but I really don't recall the reason I didn't like them.