Overheat Issue?
 

Hello,


Last week I replaced numerous parts for preventative maintenance, namely the radiator, several hoses, drive belts, alternator side tensioner, and installed a 90C thermostat. Everything seems to be working fine, but yesterday I was out and the gauge showed it to be running hot. According to my scan tool it was running at 250F. There were no other signs of it running this hot other than what the gauge was telling me. After letting it cool down I checked the coolant level and looked for leaks. The level was fine and, no leaks anywhere. I then installed a wireless meat thermometer at the upper radiator hose (attached it with a few wraps of aluminum tape), and got my IR temp gun. From cold, all the three temps agreed with each other, but after starting it, the temps diverged right where operating temperature should be. The observed temperature at the upper hose was 188-190F according to both the meat thermometer and my IR temp gun. The temperature at the lower hose, as measured with the IR temp gun was 90F. The temperature according to the scan tool however, went all the way back up to 250F. Now, based on all my past experience I have to say the temperature sensor is bad. No where on the front of this engine do I get temps higher than 190F. Do you agree? I have ordered a new sensor, which I understand to be the one on the pump.

If you have the M54 the coolant temp sensor is at the back of the cylinder head.

Overheat Issue?
 

There's a known bug that will report over temp on m54. It happened to me twice. I knew it was an error the first time becusse it was about 10F ambient and I only was ten minutes into my drive. I put my hands on the upper hose and it was maybe 140F.

I cycled power to the engine and there computer reset and showed the dash temperature simulator in the blue zone not even warmed up yet.

Since you power cycled the engine and ECT still shows high after I think you're on the right track to replace the sensor.

It's way in the back! I changed mine out during a coolant system maintenance cycle.

Unless there's something I don't know, OP's sig says 4.4 and the 3 replies so far refer to the M54.

In general, if not the sensor problem, I'd consider the possibility of an air (or other gas) pocket, which could allow the sensor to get very hot.

Yes, it's the M62 engine. Driving my daughter to gym class I got a coolant temp alarm, gauge just touching the red zone. I brought my IR temp gun and got 165F on the water pump by the temp sender, 190-200F on the upper hose...not sure what the different readings mean there. Pretty darn sure it's not overheating at all, but it's pretty unnerving driving around with that warning on the gauge cluster.

Those are normal sounding temps

Attachment 83704
PDF of the repair procedure


Sent from my iPhone using Tapatalk Pro

Thank you very much for the PDF. I am second guessing myself now...By the time I got home last night the temperature on the upper radiator hose reached 220F. After doing some reading, it looks like the actual temperature of the coolant is probably considerably higher. Perhaps in the test I did yesterday I did not allow it to run for a long enough period of time. Another thought occurred to me. Although strangely coincidental, the mechanical fan doesn't appear to be moving any air at all...well, barely any. When shut off at full temperature, the fan spins loose as a goose. But...the electric fan works and, even if BOTH fans were inoperative, forward momentum on the freeway should provide plenty enough air to keep the engine cool, wouldn't it? And the temps seem to climb regardless, based almost entirely on how long the engine has been running, not whether you're at low speeds or high speeds. I attached a picture from the application on my phone for the wireless meat thermometer I attached to the upper radiator hose. You can see it increase while running. The sharp decrease is after a stop, several very short ones, and then one long one, almost an hour. This is really starting to stump me...

I thought I was looking a yr a graph from car feedback.

On M62 the temp sensor seems to be right at the base of upper hose going to the radiator. If there's air in the system tye sensor can read high so are you sure it's completely bled?

My car with N55 regularly reports 107c=224.6 f and drops to about 94c=201.2 f under high load.

I don't recall what the normal range is but I don't see anything especially concerning from the graph.

If the AC is on the aux fan should kick on at lower temps but I think when re-reading your post you found the problem.

The clutch fan should be loose when engine is cold and stiff when it warms up. It's not pulling the amount of air though that it should.

That alone can cause the symptoms you have been describing though the aux fan should have kicked in and cooled enough to avoid a needle jump.

Stuck partially closed tstat is a very very rare condition so I would swap the clutch with an OEM part (on the board people have regularly mentioned off brand being noisy).

The wrench kit for removing the clutch fan is not ideal I has to bend a gentle "s" into it so it would catch the but heads.

There is a trick to knock lose with hammer and wrench but I busted a water pump once with that method.

When warm the clutch fan should not freewheel very long so I'm sure that clutch is shot.

Thank you very much for your input! The temp sender is on the water pump. It's a four-contact sensor. There is a second one in the lower hose at the radiator. That one, I believe from what I have read, controls the electric fan. I was able to do an active test with it using my scan tool, and it works. One experiment I wanted to do was an active test with the engine running, but with the engine on I can trigger it, but it turns off after a few seconds. As far as bleeding it goes, the procedure is simply to turn on the auxiliary water pump for some period of time. I don't think mine works...nothing happens either by triggering it with the heater controls or with the scan tool. I have one of those +the hoses on the way as well.

Just an update in case anyone happens to encounter this issue in the future. I haven't solved the problem yet, but thought I'd share what's happened so far. I installed a new auxiliary water pump and hoses and am able to observe what happens when you purge the system according to the factory procedure. I don't know why, but there is in fact a lot of air trapped that was pushed out by the little pump. You can observe a steady stream at the expansion tank with the cap removed. Because the only bleeder screw is at the expansion tank it suggests (to me) that it's the only high point in the system. I actually always wondered why the bleeder screw was there at all because you could always break the cap loose. Normally on cars with multiple volumes that trap air they provide multiple bleed points, or plumb small hoses as steam vents where applicable. Anyhow, I didn't get too far after refilling it and installing the fan clutch as I discovered a leak. One of the hoses I replaced, pt# 11537505949, the one that goes from the auxiliary water pump to the back of the engine, has a manufacturing defect. The ribbed piece that's brazed on to the metal section that in turn has a hose permanently banded to it leaks. I took the hose apart to figure this out. I've had this hose kicking around my garage since 2019, so I couldn't return it even if I remembered who I got it from. I would even scavenge the metal section from my old hose assembly except it was in the trash when it was picked up yesterday. Maybe I could silver solder it? I put in an order for a new one. Delivery time was important, so I placed the order with Pelican even though they were the most expensive at $166.00. Lastly, I did run the engine for a brief time today, and suspect bleeding it out more thoroughly, the new (Behr) fan clutch, and a new factory sending unit has not left it running any cooler. the temperature surged to 235F, with a 190F (Bremmen) thermostat after operating for maybe ten minutes. At this point I suspect the thermostat is defective. I really have egg on my face at this point considering I started out with a vehicle that ran fine. My goal was to renew the radiator, some hoses, and install a cooler thermostat. Since then nothing seems to be going right. I've never touched a vehicle that was so much trouble!