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  #21  
Old 02-01-2022, 01:30 AM
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In the M54, the thermostat wires are to send current through a heating element that will cause the thermostat to open earlier or more than it normally would. The ECU controls that current as needed based on speed and power demand. If no control current is sent, it works just like a regular fully mechanical wax thermostat.

https://us.autologic.com/news/electr...t-how-it-works

The cylinder head temp sensor, on the left side of the head, towards the rear (around cylinder 5) is what the ECU uses, and is also used for the temp gauge on the instrument panel (although by default the mapping from temp to needle angle is not linear).

The temp sensor in the lower radiator hose is used to control the speed of the auxiliary fan.
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Last edited by oldskewel; 02-01-2022 at 01:38 AM.
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  #22  
Old 06-25-2022, 01:03 PM
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Just to add to this a bit, I recently had a head gasket scare when I had a bit of coolant push out while the engine was idling in the driveway after an hour drive. I have been fearing a head gasket issue since I have over 400K km on the vehicle. I took the cap off and the coolant level was actually higher than normal but as soon as I started the car gurgled and then was low but only about 2 cups. I panicked and bought an E70 at the auction the next day because I have no time to do a head gasket! In the mean time though, I kept driving the E53 and had no problems other than maybe a bit of antifreeze smell from what I think was a bit of gas venting from the cap. Anyway after driving and playing around with it a bit I think I have come to the conclusion that the problem is actually water pump cavitation probably made worse by the fact that I am using the 1.2 bar cap and I pin the gas peddle on the highway once in a while to free up the rings when the engine starts using oil. I tested this a bit by turning the heater on with the key on but engine not running, cap off and sure enough the the aux coolant pumped through some bubbles and the coolant level dropped again! This doesn't seem to show up in cold weather when the heater is being because the bubbles get pump through the heater core by the aux pump. So I have since driven a few thousand KM without revving the engine, or turning the heater on for a few seconds after I do, and everything has been perfect! Not totally sure yet, but it's definitely looking good so far! I ordered some of the Red Line water wetter to see what that does for the cavitation but I really would like to keep using the 1.4 bar cap if I can.

To update this -- everything is still pointing to water pump cavitation maybe even caused by or made worse by the metal impeller ??
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Last edited by 80stech; 07-09-2022 at 01:08 PM.
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  #23  
Old 06-25-2022, 06:39 PM
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Some updates on this situation, now that I am spending more time at home again...

I am concluding I do have a problem, but am trying to be extra cautious before tearing into things. Last thing I'd want to do is to rebuild something and then find it was unnecessary or that I missed the one hidden thing that actually needed to be fixed. Like what do I do if I take everything apart, and don't find anything wrong? If head gasket, head, etc. all look good, what do I do?

Even though I always was confident in bleeding this system, I went and bought a vacuum bleeder, bled extra carefully, pretty sure it's well done. Good to have a new tool, but I don't think this really mattered.

I made several attempts at doing a Lisle block test for combustion gases, none of which showed a positive result. I think I DO have combustion gases getting into the coolant, but the problem is not yet bad enough to get the block test to trigger.

At some point, I swapped in a brand new expansion tank cap. Both Rein brand, both 2.0 bar. The old one was installed when I did the engine work 4 years and ~25k miles ago, so still pretty new by my standards. But the new one definitely seemed to hold tighter. It does not overflow unless driven for many (>20 or so) miles now, vs. the old one would release earlier.

A very important clue is that the system will hold pressure indefinitely. So ... engine cold, coolant bled carefully, level set, at atmospheric pressure, good. Drive somewhere, return, let system cool down to ambient temp over a day or more ... the radiator hoses will be cold but pressurized, and will remain that way indefinitely. Fully repeatable, releasing pressure, etc. does this.

Conclusion from that is that when the engine is running, combustion gases get into the coolant, pressurizing it, remaining there ... AND (since pressure holds high indefinitely) not then relieving pressure by forcing coolant or gas back into the cylinders.

I bought a nice new KleinTools borescope, ready to look into the cylinders if I thought it would help. But with pressure holding, I doubt I would see anything.

So now I am in a situation that the car is being used regularly (almost daily) for short trips and there is no overflow ever and no problems. Weird, but OK. Kind of waiting for things to get worse enough that I can accurately isolate the problem, then fix it.

Open to any suggestions.
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  #24  
Old 06-25-2022, 07:26 PM
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Even a small amount of coolant getting into the combustion chamber will probably erode (or at least discolor) the spark plug over time even if it's not enough coolant to show up in the cylinder on an overnight pressure/leak test. I think a small crack in the cylinder head also will more likely to close back up when cold. If you can put in a tee or adapter fitting so you can pressure test with the cap on then you can test the cap at the same time. I'm planning on putting that in on the E70. Have you had air trapped in the heater core that bubbled through with the heater valve open and the aux pump running?
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  #25  
Old 06-25-2022, 07:50 PM
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The biggest thing that scares me about doing a head gasket would be needing to use the time serts or big serts if Helicoils don't work ?? I can't see how any insert that is bigger than the bolt hole in the gasket does not compromise the clamping force or seal. No way is the top flange going to be perfect unless it's machined down with the block and even then the head bolt will be pulling on it before it pulls on the block unless maybe it's locked into place with maybe Loctite and/or/ more torque than is put on by the head bolt.
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  #26  
Old 06-25-2022, 09:03 PM
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Can I suggest again that you swab the cylinders one morning after running the day before?

Your description of pressure in the cooling hoses lasting sometimes days after running it is exactly what I had. I agree it sounds like exhaust pressure entering the cooling system...what tends to happen, is that after the car is shut off the excess (higher) pressure in the otherwise sealed cooling system forces coolant back into cylinders.

I mentioned earlier in this thread that I had to re-do a head gasket on my 3.0 E53...I now believe that due to failures in both the elect aux fan in front of radiator AND the fan clutch behind the radiator, My E53 overheated when my kids were driving it and warped the head. It overheated later on me in traffic AFTER I discovered coolant in cylinder 6 and did the head gasket a second time. I replaced both the inop aux fan and the fan clutch and no problems since.

Oldskewel please swab your cylinders one morning.

Last edited by Effduration; 06-26-2022 at 06:16 AM.
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  #27  
Old 06-25-2022, 09:09 PM
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Quote:
Originally Posted by 80stech View Post
The biggest thing that scares me about doing a head gasket would be needing to use the time serts or big serts if Helicoils don't work ?? I can't see how any insert that is bigger than the bolt hole in the gasket does not compromise the clamping force or seal. No way is the top flange going to be perfect unless it's machined down with the block and even then the head bolt will be pulling on it before it pulls on the block unless maybe it's locked into place with maybe Loctite and/or/ more torque than is put on by the head bolt.
Do Not do a head gasket unless you are sure it is your problem..Head gaskets don't usually fail just because of mileage.

BUT, this shouldn't scare you in the least... The E53 is a great car to do a head gasket on...The car stays on it wheels the whole time and there is a ton of access on the 6 cylinder E53's. I have done it twice on an E53...

Forget about using helicoils..wrong application. Go right to regular time-serts. I am happy to rent you Time-sert kit 1090 and offer every pointer I have. I have time-serted 10 M54's including one this week. The 1090 time-sert drill bit leaves a 6mm (3mm?) countersink, so the insert flange is well below the block surface.

Last edited by Effduration; 06-26-2022 at 06:34 AM.
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  #28  
Old 06-25-2022, 11:11 PM
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Wow, you guys are on it way faster than I am. Thanks!

OK, I will borescope and "swab" the cylinders. By swab, I will assume you mean put a q-tip or equivalent in there to see if I can detect any back-pressured coolant, right?

To remind you of my previous work on this. Before I bought the car in 2014, the PO (second owner, who had it from about 50k miles to 169k when I bought it) spent about $13k over 18 months at the dealer on it, following a CCV failure it seems. Possible overheat / cooling issue as well, as may be indicated by dealer repair receipts, but not sure. So the engine / head could have been pre-warped when I bought it in 2014.

Then in 2018, the upper radiator hose blew out (not sure if it failed first, or the cooling system over heated first), leading to a similar situation that I'm in now. I replaced the radiator, hoses, and a few other things, then found coolant overflowing and that I had combustion gases, etc. So it was similar to now, but far more severe, and easy to confirm I had a head problem (ended up being warpage). In that case, the pressure would eventually subside, and I did detect coolant inside the cylinders, following pressurization with the method shown below.

(still in 2018) I took it all apart, had the head pressure tested, cleaned, and fly cut (not enough taken off to warrant the thicker HG, so not too bad). HG had been OK, no cracks in the head or block. TimeSerted with the regular sized ones, done carefully by hand, with the block in the car. Tuned up a crap ton of other stuff "while I was in there" LOL. VANOS rebuild, starter rebuild, full gasket kit, new anything that might be needed. Cams, valves, pistons, everything looked really good. This was all about 20k miles ago in 2018, and it was perfect until this recent issue.

So I believe in the magic of TimeSerts, but while doing it, it sure seemed that the engine block aluminum was weaker than it should be. Closer to butter than to steel, it seemed. I can believe that overheating weakened it. I was sweating as I was carefully torqueing down the head afterwards, just hoping things would hold.

I can also definitely pressurize the cooling system with the cap in place. Here is a cool method found on the internet (LOL, me)
https://xoutpost.com/bmw-sav-forums/...ystem-e53.html

And as far as what might have caused a failure - maybe assume a non-perfect head repair existed (e.g., undetected crack) with no problems for 20k miles, then last fall, my daughter took the X5 down to SoCal to continue school and maybe some hard drives up and down the grapevine mountains, etc. may have pushed the weakness to where it is now, still not broken, but showing the problem.

But here's a basic belief I currently hold (willing to update though): For the situation I described, where pressure appears and remains even after things fully cool down, there is no possible explanation other than combustion gases, right? Added "test": if it starts out cold and unpressurized, and I let it sit for several days, it remains unpressurized (to rule out some reaction creating gas). Right? So I MUST have combustion gases getting in, even though my block test can't yet detect it. BTW, my block testing 4 years ago (same Lisle kit) was easily conclusive.
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Last edited by oldskewel; 06-25-2022 at 11:19 PM.
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  #29  
Old 06-26-2022, 06:31 AM
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Quote:
Originally Posted by oldskewel View Post

OK, I will borescope and "swab" the cylinders. By swab, I will assume you mean put a q-tip or equivalent in there to see if I can detect any back-pressured coolant, right?
......................
So I believe in the magic of TimeSerts, but while doing it, it sure seemed that the engine block aluminum was weaker than it should be. Closer to butter than to steel, it seemed....................

But here's a basic belief I currently hold (willing to update though): For the situation I described, where pressure appears and remains even after things fully cool down, there is no possible explanation other than combustion gases, right? ....

Yes on q-tip..I securely taped half a q-tip to a 1-foot piece of flex hose. But since you have a borescope, I would scope first then swab remembering that pistons are tilted toward exhaust.

As for soft aluminum, A sharp (new?) drill bit will go thru the alum M54 head bolt threads like butter..When drilling, you are really just reaming out the old threads, A new tap also cuts new threads quite easily.

I don't have another explanation for excess & persistent pressure in cooling hoses, but I am a little puzzled as to why your tester would not see exhaust gas in coolant...
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