My lower radiator hose is always cold, even after t-stat replacement - BMW M5 Forum and M6 Forums
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post #1 of 7 Old 3rd February 2012, 02:57 AM Thread Starter
Dob3rman
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My lower radiator hose is always cold, even after t-stat replacement

Hi guys!

Please help with my thermostat problem. My lower radiator hose had always stayed cold and I thought my t-stat stuck closed so I ordered a new t-stat from pelicanparts and had it replaced. Now, my lower hose still stays cold... The engine temp gauge is at the middle, so I guess nothing is overheating. My upper radiator hose is always hot (as I should be). Do you guys think it's normal or not? My old t-stat was dead for sure (I boiled it but it never opened).
(e39 540i M62/TU)

Thank you for help!

Last edited by Dob3rman; 3rd February 2012 at 02:59 AM.
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post #2 of 7 Old 3rd February 2012, 06:17 AM
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Quote:
Originally Posted by Dob3rman View Post
Hi guys!

My old t-stat was dead for sure (I boiled it but it never opened).
(e39 540i M62/TU)
Have you boiled the new T-Stat to check it opens?

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post #3 of 7 Old 3rd February 2012, 09:57 PM
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540 has something different about it, can't remember what it is. If Matt does not respond you will not likely get much other expertise. Your car is not the same as an M5 for many reasons and the cooling system is one. Sorry wish I could help.
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post #4 of 7 Old 4th February 2012, 02:25 AM Thread Starter
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Quote:
Originally Posted by x-fire View Post
Have you boiled the new T-Stat to check it opens?
Nope I definitely should have done it.
Today I ran OBC test #7 at idling and the engine temp was 108-109°C maximum but my main fan never sped up.
Our t-stats are electronically controlled, so can it be that they open a little to pass a little amount of coolant just to keep engine temp stable? If so, the lower hose wouldn't really have time to get warm... Otherwise I don't know what to think.

Last edited by Dob3rman; 4th February 2012 at 02:28 AM.
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post #5 of 7 Old 4th February 2012, 02:38 AM
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It sounds plausible. If you are not registering hot on the dashboard, then it might be normal operation.

Have you asked your local dealer/mechanic?

Objects in the Mirror are Losing


26 Aug 2014 - 172852kms - New Bank 1 VANOS Unit and replaced Bank 2 Intake Camshaft Sensor
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16 May 2014 - 169882 kms - New Front shock absorbers, Front Thrust Arm bushes, Rear upper control arm bushes, Suspension level sensor, Rocker Cover Gaskets, Engine Vent Pipes & Breather Hoses, and RHF Door Seal. Reseated LHF Spring Pad and Both Rear Brake Discs replaced under Warranty. Full Wheel Alignment
08 Apr 2014 - 168104 kms - 2 New Front Tyres (Bridgestone Potenza RE50A RFT)
01 Apr 2014 - 167779 kms - Inspection 2 Service
19 Dec 2013 - 163365 kms - Replacement Front Tow Eye Cover
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10 Sep 2013 - 160000 kms Milestone (less than 1000 kms to the 100,000 mile mark)
01 Jul 2013 - Puncture - 2 New Rear Tyres
(Bridgestone Potenza RE50A RFT)
25 Mar 2013 - 150000 kms Milestone

04 Mar 2013 - 148435 kms - Repaired broken cup-holder
28 Feb 2013 - 148355 kms - New Stock Clutch and Flywheel, jetwashed fuel tank, new fuel pump and filter, and replaced hazard button in console
05 Feb 2013 - 147659 kms - New Tailshaft Artic Disc (Guibo)
19 Jan 2013 - 147212 kms - New Stock Airfilters and Cabin Filters
22 Dec 2012 - Obtained Peake Code Reader
23 Apr 2012 - 146003 kms - Replaced Rear Wheel Bearings
06 Feb 2012 - 141515 kms - New Front Brake Pads and Sensors
28 Dec 2011 - 138938 kms - Oil Service and Safety Check
18 Aug 2011 - 125412 kms - Purchased Car (Replaced 2 rear tyres shortly after purchase)
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post #6 of 7 Old 5th February 2012, 07:10 AM Thread Starter
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Quote:
Originally Posted by x-fire View Post
It sounds plausible. If you are not registering hot on the dashboard, then it might be normal operation.

Have you asked your local dealer/mechanic?
Yes, I have. He said as long as my aux fan doesn't engage and the temp is not getting over 110 degrees Celsius, everything is fine.
My new t-stat actually opened once but to make it open I had to run my engine at 2500rpm straight for 10 min and only after that my lower rad hose got hot.
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post #7 of 7 Old 5th February 2012, 07:17 AM
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Check out the info on this site.

http://www.meeknet.co.uk/E31/M62B44_Engine.pdf

It looks like for the M62, the wax pellet on its own doesn't open the t/s until 103 deg C, so the boiling water test is no good for testing it. Looks like there was anything wrong with your old t/s.

The above also shows the normal part-load coolant temp being 109 deg C, exactly what you are seeing. It is not unusual for a t/s not to open at all in cold climes like NY under light driving conditions, especially with an aluminum engine.

What puzzles me is that you are feeling the upper rad hose hot. It shouldn't be if the t/s is not opening. It should also be cold or maybe warm, not hot . How hot is it?
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