Water Temp Fluctuation - Rising while driving. Normal when idling

[AWE46M3]

EDIT: See 8/3 post on page 2 for the resolution update.

2 part issue and resolution:

1. Initial overheating resolved by cooling system refresh. Temp gauge did not pass the dot between center line and adjacent dot as pictured below. OEM BMW radiator, water pump, aux fan/temp switch, radiator hoses, and high temp o-rings were replaced. Thermostat, oil/coolant temp sensor, and expansion tank were recently replaced and left along with the aux fan and fan clutch.

2. Water temp needle position may have gotten thrown off during the overheating episode, resulting in a needle position that was off center despite optimal coolant temps. I performed a gauge cluster reset to realign the needle. Everything is dead center after the cluster reset (video linked in my response - post 29, page 2) and the system is cooling perfectly.


Original post from 6/22/23:

Hello Group,

My alternator has been on the fritz for a while and I had it replaced last week. When I was driving to the shop, I noticed my water temps (which are usually dead center - I can't see the thermostat image) were leaning to the hot side slightly (I could see the thermostat). I didn't think anything of it and didn't bother mentioning it to my shop in case it was a fluke.

I took the car for a short drive this evening and noticed the water temps were climbing by the time I hit 3rd gear / 40 MPH. Oil temps were well below 200. The warm up lights had just turned off by the time I noticed the water temps were rising. It's 70 degrees out and I was not running the AC. I pulled over, turned the car off, and checked to see if there were any leaks or obvious issues and did not see anything.

I turned the car on and began driving to the shop that replaced my alternator...Water temps returned to normal after the 3-minute turn-off period. I noticed the water temps start to rise again as I shifted to 3rd gear approaching 40 mph. Picture of my water temps around 55 mph cruising on the freeway for a few minutes:





By the time I reached my shop and let the car idle, the temps went down and sat just above dead center (where I can see the thermostat) and did not climb back up to the 3rd dot. Picture below:




The water temps were up slightly the day I dropped the car off for the alternator job but never got anywhere near the 3rd dot. My shop insisted a little beyond dead center was normal, but agreed to do look the car over. Any feedback you can provide to help me nudge them in the right direction would be much appreciated. Never delt with overheating issues with an E46 and know this stuff can be quite the puzzle to solve. Thanks in advance.

[Pklauser]

Might be useful to know you can see the actual temp values by doing the following: https://www.bimmerforums.co.uk/threa...80/post-611649

[maw1124]

I know fan clutches on these are an issue but I know nothing about your car, so just check to see if that’s been done yet. It may be due on time, mileage or both at this point (+20yrs).

The fact that heat us building under load but not at idle leads me to question exhaust, specifically whether cats are clogged (not letting hot exhaust gasses out the back). But before I get there I’d look at fan clutch.

These are WAGS and should be regarded as simple food for thought.

maw

[AWE46M3]

Fan clutch may have been replaced by the previous own - the blades are in great shape and the fan itself is running at idle. It could be running at a lower speed than it needs to when the car is under load at higher temps - great call out.

If the cats were clogged, I’d have a CEL, wouldn’t I? I am switching from US catted headers to OEM CSL headers and catted section 1 this summer - if cooling system checks out, we’ll see if that helps at all.

[maw1124]

Yeah, I’m never sure what level of malfunction throws a CEL on which cars these days. I know I’ve modified exhausts so they never throw a CEL, moved O2 sensors downstream of the secondaries so the flow has been cleaned twice, all kinds of stuff happens on cars this old. So not knowing your car, I threw that out there. All that said, it’s a couple degrees either way so I’m not expecting a huge problem. And since you’re changing your exhaust anyway this summer, time will overtake the 2 ideas I suggested.

GL

maw

[AWE46M3]

Yeah, I’m never sure what level of malfunction throws a CEL on which cars these days. I know I’ve modified exhausts so they never throw a CEL, moved O2 sensors downstream of the secondaries so the flow has been cleaned twice, all kinds of stuff happens on cars this old. So not knowing your car, I threw that out there. All that said, it’s a couple degrees either way so I’m not expecting a huge problem. And since you’re changing your exhaust anyway this summer, time will overtake the 2 ideas I suggested.

GL

maw

Thanks brother - Appreciate you taking the time to throw some ideas out there. I'll update the thread once we pinpoint the issue.

[AWE46M3]

Did some research and I am thinking this could be an issue with my fan underperforming. Considering an electric fan conversion at this juncture if the cooling system is verified with no issues tomorrow.

Found this old build journal article: https://thebuildjournal.com/diy-inst...fan-mount-diy/


Anyone have strong opinions about Spal fans? I've seen threads with people stating they've deleted their clutch fan and run the AC fan only. I am puzzled how that works but apparently, it does.


Only big down side I can see to a Spal fan is the run the entire time the car is on. Any other cons to be aware of when considering an electric fan conversion?

[IamFODI]

Did some research and I am thinking this could be an issue with my fan underperforming. Considering an electric fan conversion at this juncture if the cooling system is verified with no issues tomorrow.

Found this old build journal article: https://thebuildjournal.com/diy-inst...fan-mount-diy/


Anyone have strong opinions about Spal fans? I've seen threads with people stating they've deleted their clutch fan and run the AC fan only. I am puzzled how that works but apparently, it does.


Only big down side I can see to a Spal fan is the run the entire time the car is on. Any other cons to be aware of when considering an electric fan conversion?

Obioban

[Obioban]

Fans keep the car cool when you are stopped. Air flow from motion keeps the car cool when you're moving. Your issue is not when you're stopped, so I don't think anything fan related will help anything.

As in, for context, I only have a SPAL fan (no other fan), and I have it programmed to turn off completely at 35mph.

What cooling system components are you running, and how many miles on them?

[Casa de Mesa]

Fans keep the car cool when you are stopped. Air flow from motion keeps the car cool when you're moving. Your issue is not when you're stopped, so I don't think anything fan related will help anything.

As in, for context, I only have a SPAL fan (no other fan), and I have it programmed to turn off completely at 35mph.

What cooling system components are you running, and how many miles on them?

Agree with this. I don't run a fan on my racecar at all, not even an electrical one. Fans impede airflow once you're moving above a certain speed.

Is the pusher fan up front seized and blocking airflow? That *might* be the cause for the slightly elevated temps at speed, but think it could be other components in the system.

[AWE46M3]

IamFODI - thank you for the tag

Fans keep the car cool when you are stopped. Air flow from motion keeps the car cool when you're moving. Your issue is not when you're stopped, so I don't think anything fan related will help anything.

As in, for context, I only have a SPAL fan (no other fan), and I have it programmed to turn off completely at 35mph.

What cooling system components are you running, and how many miles on them?

This is great information to have - thank you. The clutch fan under performing was my initial theory...back to the drawing board. The cooling system appears to be relatively new - the expansion tank and clutch fan both look like they have less than 10K miles on them. I'll have the shop go through all the hoses and caps. If i had a leak in the system, I would be overheating regardless of operating speeds, correct?

No other obstructions to note. The system is completely stock and all OEM parts.

[bigjae46]

Yes, fans degrade cooling at higher speeds.

My bet is it’s a water pump. Check for play in the shaft or pull the thermostat and check.

Here’s what mine looked like when - with no fans - performed normally at idle but ran hotter at speed.

[AWE46M3]

Quick Update from my Shop:

They inspected all my connections, tested both of my fans, and ensured the thermostat and other sensors were operational. No faults or errors logged. I am going to pick the car up this afternoon and will likely spring for a new OEM Radiator, Water Pump, and hoses. I'll bump this thread after that work is completed and let everyone know the culprit. It's still a mystery at this juncture.

Car did not heat past the center line at idle during all of their testing. Car only starts overheats when it's brought up to 40+ mph's so I need to document my replication steps a little better and start throwing parts at this thing.

Drove the car home with the AC on and the car did not overheat (some help to the cooling system from the electric fan). Water temps started to climb as soon as I turned the AC off and reached 40-50 MPH

[sapote]

"Considering an electric fan conversion at this juncture if the cooling system is verified with no issues tomorrow."
I would stick with the clutch fan instead of the conversion. Even with a bad clutch fan, no overheat should happen if the elec fan in front is working properly.

At operating temp, grasp the rad lower hose and see how long you can hold it without crying. If not hot then you have coolant flow issue.

[AWE46M3]

"Considering an electric fan conversion at this juncture if the cooling system is verified with no issues tomorrow."
I would stick with the clutch fan instead of the conversion. Even with a bad clutch fan, no overheat should happen if the elec fan in front is working properly.

At operating temp, grasp the rad lower hose and see how long you can hold it without crying. If not hot then you have coolant flow issue.

Do you recommend doing a full system flush and seeing how system performs thereafter? Thinking about flushing the system and maybe installing a new radiator - my current radiator appears to be the original one and may be gummed up.