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Expansion tank level going up...

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randall977
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Expansion tank level going up...

Post by randall977 » Wed Jun 12, 2019 8:29 pm

My car isn't back on the road yet so I've not given it a good test, but I have driven it up and down the drive and run it many times. The engine runs very nicely with no issues apart from one... After about half an hour of idling the expansion tank fills up right to the top - this is when I normally turn the engine off. The hoses look fine, there are no black (or other) particles in the coolant, the temperature does go up, but it comes back down - the needle is sometimes a bit erratic.

My thoughts are of head gasket issues, so I bought an adapter to be able to do a compression test. I used the tool on my CSi and it was fine, however, on this M88 engine the pressure only went up to 70psi - though exactly the same on all cyclinders. Clearly the engine wouldn't run if it really was 70 psi. The tool doesn't seem to be leaking - maybe the adapter isn't sealing? I did the test three times, hot and cold. It's annoying as any inconsistency in cylinder pressure is hard to spot at this low pressure.

So, if it wasn't the head gasket, what could be causing the coolant to rise in the expansion tank? I recently replaced the non-original 1.5 bar expansion tank cap with the genuine 140psi one (I think it's 140 as this is faintly stamped on one side).

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TBM
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Re: Expansion tank level going up...

Post by TBM » Thu Jun 13, 2019 3:43 pm

Randall,

These cars also have an issue with the 6th Cylinder heating up more as the engine is long. I had idling heat up issues. You should replace the water pump pulley to a e34 M5 piece as it is smaller and move the coolant faster. It helped my car stay cooler. My area can get quite hot in the summer time.

Also, as typical coolant needs pressure in order to lower the boiling temperature and you seem like a very handy restorer (maestro is more like it) You should consider to move to Evans coolant as it doesn't need to build pressure in the system and puts a lot less stress on your hoses and other connections.
You will of course have to completely evacuate the system of all water/coolant.

http://www.evanscoolants.co.uk
'84 M635csi
'86 Lotus esprit Turbo (sold)

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randall977
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Re: Expansion tank level going up...

Post by randall977 » Thu Jun 13, 2019 5:26 pm

Thanks TBM! I have dabbled with Evans, the flushing side of things puts me off, but in principle I like the idea of it very much. I've ordered a hydrocarbon tester so within the next few days I will be able to confirm if it's a HG issue. If so it's annoying, but not the worst job in the world. I will look into the e34 pump upgrade...

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TBM
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Re: Expansion tank level going up...

Post by TBM » Thu Jun 13, 2019 9:46 pm

randall977 wrote:
Thu Jun 13, 2019 5:26 pm
Thanks TBM! I have dabbled with Evans, the flushing side of things puts me off, but in principle I like the idea of it very much. I've ordered a hydrocarbon tester so within the next few days I will be able to confirm if it's a HG issue. If so it's annoying, but not the worst job in the world. I will look into the e34 pump upgrade...
You're Welcome Randall,

BTW the part number for the pulley is: 11-51-1-315-202
As a comparison: m635 pulley: 130mm M5 pulley: 102mm difference is about 22% smaller. You will of course need a smaller belt

It brought my needle down from 3/4 to just above half without doing anything else.
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'84 M635csi
'86 Lotus esprit Turbo (sold)

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randall977
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Re: Expansion tank level going up...

Post by randall977 » Fri Jun 14, 2019 2:09 pm

Unfortunately the pulley is NLA, I'll have to keep an eye on eBay...

I carried out the hydrocarbon test today - the engine needs to be run for at least 2 minute, if hydrocarbons are present the blue liquid turns yellow. The photo below is after 7 minutes - good news!

HCT.jpg
HCT.jpg (111.28 KiB) Viewed 219 times
Afterwards I blew the liquid out of the tube and it tuned yellow immediately - bad breath? :oops:

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randall977
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Re: Expansion tank level going up...

Post by randall977 » Fri Jun 14, 2019 8:35 pm

Turns out the viscous fan isn't engaging...new coupling on order

Does the electric fan only come on with the a/c?

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Re: Expansion tank level going up...

Post by hornhospital » Fri Jun 14, 2019 10:45 pm

The electric fan is supposed to come on when the coolant reaches a certain (REALLY HIGH) temperature, but normally it runs only when the A/C is on.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'87 325is "Odette"; '93 325is "Elvira"; '95 M3 "Ashlyn"; '95 318is "Bebe"

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randall977
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Re: Expansion tank level going up...

Post by randall977 » Sat Jun 15, 2019 2:17 pm

99 degrees I think, it did come on!

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randall977
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Re: Expansion tank level going up...

Post by randall977 » Wed Jun 19, 2019 6:57 pm

To conclude this thread - it was the viscous fan coupling of course. It now holds temperature fine. It's good to know that my head gasket is fine though!

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Re: Expansion tank level going up...

Post by Hefeweizen » Thu Jun 20, 2019 2:30 pm

Thanks for the close out!
Rainer
03 330Xi (DD)
85 635CSi (RIP 3 May 19)
80 633CSi (Red Euro, Project)

"If you think a good European mechanic is expensive, try a bad one!"

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