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Discussion Starter · #1 ·
After doing some work on the cooling system (thermostat, hoses, water pump, expansion tank, flush) I bled the system a few times.

On the top of the expansion tank there's a stream of coolant that comes out from the upper radiator hose that connects between the expansion tank and the thermostat.

Normally at idle no coolant streams out of this hole but when I rev the engine coolant streams almost constantly. At one point when I was doing a subsequent bleeding I noticed that the coolant started to rise up a lot in the expansion tank neck and coolant was streaming out of that hole occasionally at idle rpms but most of the times it doesn't.

Is there a valve that determines when that opens and what type of valve is it? Is the valve in the expansion tank or in the hose? Any info I can glean from the valve opening and closing?

I'm occasionally seeing coolant on top of the expansion tank. Either from the cap or from the connection where the upper radiator hose attaches to the tank. Trying to track down what might be the issue.

Last night I put some plastic wrap and a rubber band over the expansion tank fill holeto see if it bubbled up and it didn't. I checked the combustion chambers with an inspection scope and uv light (uv dye in coolant) and didn't see any indications of coolant in there. Not having any overheating issues, temperature is actually showing up very good. Used a block tester to test for signs of exhaust gases which came up negative. Kept the tester over the hole for longer than instructions said, maybe 20 minutes to test while engine was cold and hot.

In the meantime I replaced the expansion tank cap with a 1.2 bar cap from German Auto Solutions to be on the safe side.

Any idea what's going on?
 

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On the top of the expansion tank there's a stream of coolant that comes out from the upper radiator hose that connects between the expansion tank and the thermostat.
given that tank cap and the bleeder screw are tight there shouldn't be any coolant stream in that area. If there is, replace the failing parts.

There is no valve in the entire cooling system except the thermostat and the cabin heater lines. What you experience is that when revving the engine the water pump spins faster and pushes out the coolant.
 

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Discussion Starter · #3 ·
given that tank cap and the bleeder screw are tight there shouldn't be any coolant stream in that area. If there is, replace the failing parts.

There is no valve in the entire cooling system except the thermostat and the cabin heater lines. What you experience is that when revving the engine the water pump spins faster and pushes out the coolant.
If it changes your answer... I meant a stream on the inside of the expansion tank up the filler neck. The stream that comes out at 1:45 in this video. https://drive.google.com/drive/folders/0B-mug2NCeAc2VFh0d0tUSjJkZkU

I have seen it stream out when the engine was idling at least once but most of the times it doesn't.
 

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Discussion Starter · #5 ·
Any idea where that coolant stream comes from? I looked at my old expansion tank and it looks like the upper radiator hose port goes down into the tank. I'm wondering if seeing it stream when the engine wasn't running may indicate something like a clogged/ing radiator or anything else?

Swung by Rennsport Motorworks in Hackensack NJ with the intention of doing a pressure test. Sal took a quick look and found the leak was at the connection of the upper radiator hose to the expansion tank. There are two connections next to each other and it was the small one.

So either bad hose, bad tank or I didn't do a great job making the connection which would be my first guess. Will check that connection and go for a test drive.
 

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Any idea where that coolant stream comes from? I looked at my old expansion tank and it looks like the upper radiator hose port goes down into the tank.
have you seen the picture I attached in the previous post?

when the thermostat is closed, there are 3 ways the coolant can circulate.

1. the main route is circulating inside the engine
2. route is the cabin heater core: water pump - engine head - ihka - bottom of expansion tank - distributor below expansion tank - return pipe to engine
3. route is what you are chasing: water pump - engine head - upper radiator hose - expansion tank - distributor below expansion tank - return pipe to engine
 

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coolant hose O rings are available separately

don't forget you buy the coolant hose O rings too

example below from bmp

http://www.bmpdesign.com/product-ex...egory_id/149/search_year/2000/search_model/72

BMW Coolant Hose O-ring for 1.5" Fitting

Part Number: 115242

This item is eligible for Free Shipping on any order over $150
Coolant hose O-rings

Many of the new generation BMW's and Mini Cooper's have quick disconnect water hoses. This system utilize an Oring seal inside the plastic connectors. If you are planning to replace hoses then new O-rings are already included.

If you are only replacing a coolant tank, radiator, or thermostat you should make it a point to replace the hose end O-rings. If your planning on using the old O-rings you run the risk of have a new leak. O-rings will flat spot over time, or may become damaged in the removal and re installation process.

Note: This medium size 1.5" O-ring is typically used on heater, aux. pumps, return hoses, and coolant tanks.
View all BMW models that this part # 115242 is compatible with! VIEW BMW APPLICATIONS
 

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And of course that new hose has to be pushed on until you clearly hear the clip click.

I'm occasionally seeing coolant on top of the expansion tank. Either from the cap or from the connection where the upper radiator hose attaches to the tank. Trying to track down what might be the issue.
If new expansion tank cap doesn't solve that issue,

possible that aftermarket hose used and it doesn't mate well with O.E or aftermarket tank?
 

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Discussion Starter · #9 ·
have you seen the picture I attached in the previous post?

when the thermostat is closed, there are 3 ways the coolant can circulate.

1. the main route is circulating inside the engine
2. route is the cabin heater core: water pump - engine head - ihka - bottom of expansion tank - distributor below expansion tank - return pipe to engine
3. route is what you are chasing: water pump - engine head - upper radiator hose - expansion tank - distributor below expansion tank - return pipe to engine
I saw the image but it doesn't give details on the part I'm talking about. The coolant from the upper radiator hose into the expansion tank goes straight down after it enters the expansion tank. Fed some twine in the hole in the old tank and only place I could get it to go was down.

Up towards the top of the filler neck is the hole for that stream I mentioned. When revving the engine coolant will start to flow from there. See pic. Put some plastic wrap over it so I don't splash my phone.

Wondering where the coolant comes from to make that stream and if knowing how it gets there can indicate anything useful. Under idle not even a trickle seems to come out that hole, as the coolant expands it expands from the bottom.
 

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Discussion Starter · #10 ·
And of course that new hose has to be pushed on until you clearly hear the clip click.

If new expansion tank cap doesn't solve that issue,

possible that aftermarket hose used and it doesn't mate well with O.E or aftermarket tank?
BMW hose, after market tank. Think problem may have been user error. Ran into a problem with the AT thermostat that held me up and was pretty late when I finished things up. I probably didn't put the hose on correctly. Small chance it slipped off after the fact but will keep an eye on it. After engine cooled down enough tried to reseat that connection. Went for test drive and appears to be fine. After having a hose blow I was probably nervous about pressure in the cooling system but it seems fine.

Hoses feel stiff from pressure but nothing coming out of cap. Put on the 1.2 bar cap so less than that in system.
 

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You seem to be the person that can never be satisfied. :thumbdwn:

have you ever said THANK YOU to anyone? :rolleyes:

yes your model doesn't have an aux pump. so how far can your imagination go regarding this issue? If no aux pump then possibly the main water pump is pushing the water through the cabin heater core that has a heater valve.


yes your expansion tank looks slightly different but principle is the same. what else do you want ???
 

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Discussion Starter · #14 ·
You seem to be the person that can never be satisfied. :thumbdwn:

have you ever said THANK YOU to anyone? :rolleyes:

yes your model doesn't have an aux pump. so how far can your imagination go regarding this issue? If no aux pump then possibly the main water pump is pushing the water through the cabin heater core that has a heater valve.

yes your expansion tank looks slightly different but principle is the same. what else do you want ???
Thank you for your time. The information about not having a check valve was very helpful.

I'm curious what causes the stream to come out of that top hole in the filler neck of the expansion tank and why. I know that revving the engine higher causes the coolant to stream out of there but what is it about revving the engine that makes it come out there. That is the original question I asked.
 

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Thank you for your time. The information about not having a check valve was very helpful.

I'm curious what causes the stream to come out of that top hole in the filler neck of the expansion tank and why. I know that revving the engine higher causes the coolant to stream out of there but what is it about revving the engine that makes it come out there. That is the original question I asked.
Ok, appreciate it, sorry. When revving the engine the water pump spins faster, increasing the coolant pressure so if #2 and #3 (below) haven't started circulating yet and the heater valve is open, they will. The expansion tank inlets are usually high up because it has to make sure there is no air exiting through the outlet, that is on the very bottom. Not sure what is the logic behind the heater valve, when is it on and off other than for heating.

Maybe if you disconnect the heater valve it closes, cutting off that stream. Not sure if it's off open or off closed.
https://www.google.com/search?q=+ 64118369805+

"
2. route is the cabin heater core: water pump - engine head - ihka - bottom of expansion tank - distributor below expansion tank - return pipe to engine
3. route is what you are chasing: water pump - engine head - upper radiator hose - expansion tank - distributor below expansion tank - return pipe to engine
"
 

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Thanks to both of you for getting ruffled but being big by apologizing to each other like gents. This needs to happen more on the internet.
 
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