My lower radiator hose is always cold, even after t-stat replacement

Dob3rman · 3rd February 2012, 02:57

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!

x-fire · 3rd February 2012, 06:17

Quote:

Originally Posted by Dob3rman

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?

Sailor24 · 3rd February 2012, 21:57

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.

Dob3rman · 4th February 2012, 02:25

Quote:

Originally Posted by x-fire

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.

x-fire · 4th February 2012, 02:38

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?

Dob3rman · 5th February 2012, 07:10

Quote:

Originally Posted by x-fire

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.

68FB · 5th February 2012, 07:17

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?