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Discussion Starter #1
Hey so I just bought another car. It was sitting for a while
and now it is acting funny. When I start it it gets hot fast and then stays at 98c sometimes goes up to 103c depends on how hard I push the car , it smokes more then usual but the color is not white, coolant is still at max and is still original color . anybody have a good idea where to start with diagnosis was going to get a block tester kit to see if it's a headgasket issue tomorrow but the oil looked chunky when I opened fill cap so is it possible i just need a good old oil change?? Any insight much appreciated
 

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Hey so I just bought another car. It was sitting for a while
and now it is acting funny. When I start it it gets hot fast and then stays at 98c sometimes goes up to 103c depends on how hard I push the car , it smokes more then usual but the color is not white, coolant is still at max and is still original color . anybody have a good idea where to start with diagnosis was going to get a block tester kit to see if it's a headgasket issue tomorrow but the oil looked chunky when I opened fill cap so is it possible i just need a good old oil change?? Any insight much appreciated
The thermostat could maybe be stuck closed, is there any codes in the ecu? If the car hasn't been on a long drive in a while it can cause 'mayo' build up on the cap, also have you checked the coolant for any oil contamination? That could point to possible head gasket failure.

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Discussion Starter #3
The thermostat could maybe be stuck closed, is there any codes in the ecu? If the car hasn't been on a long drive in a while it can cause 'mayo' build up on the cap, also have you checked the coolant for any oil contamination? That could point to possible head gasket failure.

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How do I know if it's stuck do I just replace and coolant looks nice and green no brown mixture I just been looking inside the expansion tank with a flashlight am I doing it right
 

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How do I know if it's stuck do I just replace and coolant looks nice and green no brown mixture I just been looking inside the expansion tank with a flashlight am I doing it right
If you have inpa or some sort of scan tool that reads bmw specific codes it should show a thermostat code or maybe point you in the right direction, but usually the thermostats fails open so the engine will run cold. Other things to check would be making sure the radiator fan is turning on, and also making sure the coolant is bled properly.

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Discussion Starter #5 (Edited by Moderator)
If you have inpa or some sort of scan tool that reads bmw specific codes it should show a thermostat code or maybe point you in the right direction, but usually the thermostats fails open so the engine will run cold. Other things to check would be making sure the radiator fan is turning on, and also making sure the coolant is bled properly.
See I just tried to do a coolant bleed and noticed my blower doesn't work could that be a cause?
 

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If its not overheating, dont worry too much. FWIW in summer with max AC and doing repeated pulls my coolant temp can creep up to 104c, just on the verge of when i'd pull over and cut the engine. 98c at idle is normal range. In summer the car easily warms up in a few minutes of idling.
 

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How do I know if it's stuck do I just replace and coolant looks nice and green no brown mixture I just been looking inside the expansion tank with a flashlight am I doing it right
Mango would not approve of green coolant.
See I just tried to do a coolant bleed and noticed my blower doesn't work could that be a cause?
Coolant bleed doesn't need the blower, and the heater valve is fully opened when the car is off.
 

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The thermostat could maybe be stuck closed, is there any codes in the ecu? If the car hasn't been on a long drive in a while it can cause 'mayo' build up on the cap, also have you checked the coolant for any oil contamination? That could point to possible head gasket failure.

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I don't think it's a thermostat issue. I've you've indeed driven it hard for some time, water temp should've climbed up really fast and way higher than 103 °C with a closed tstat.

Check that non-white smoke out again and be prepared for head gasket replacement (or not, might just be the water pump, or that tstat, or carbon buildup released after some heavy foot at work...) You should try to isolate the problem a little more.
 

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Mango would not approve of green coolant.

Coolant bleed doesn't need the blower, and the heater valve is fully opened when the car is off.
^^^This.
E46 does NOT need the ignition or heater on while bleeding. Other BMW models do.
 

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You need a new thermostat. Normal range is 78 (full beating on it) to 97/98. Sitting in traffic with fan on.

When you load it up the thermostat opens and let’s cool water into the engine. Running > 100 is bad. Replace it with an oem on from fcp euro and call it a day.


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If its not overheating, dont worry too much. FWIW in summer with max AC and doing repeated pulls my coolant temp can creep up to 104c, just on the verge of when i'd pull over and cut the engine. 98c at idle is normal range. In summer the car easily warms up in a few minutes of idling.
No it isn't normal. if temp within threshold it doesn' mean it is ok. that is how expansion tanks explode. It really shouldn't go higher than 95 on idle. Higher temp indicates soft failing thermostat or fan failure. In ambient temp 50C and ac on my temp doesn't climb higher than 93, then thermostat opens and temp goes down to 86 or so. New thermostat, bleed, 50/50 coolant mix and check fan work.
 

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I don't think it's a thermostat issue. I've you've indeed driven it hard for some time, water temp should've climbed up really fast and way higher than 103 °C with a closed tstat.

Check that non-white smoke out again and be prepared for head gasket replacement (or not, might just be the water pump, or that tstat, or carbon buildup released after some heavy foot at work...) You should try to isolate the problem a little more.
In order to meet eco standards, BMW decided to increase overall engine temperature and made "hot" thermostat controlled by DME, there is heating element which melts wax and therefore opens thermostat quicker and when it is needed, allowing to keep overall engine temperature higher and controlling it within limits. So thermostat doesn't have to stick open or closed to fail, it is enough if heater element doesn't melt wax fast enough for thermostat to react properly or to allow valve to close/ open completely. That is how you get higher temp on idle, that's how you get high temp when drive actively. soft failing thermostat won't drop code and only way to get idea about it's condition is to monitor temperature trough cluster 7 or with diagnostic equipment. 98 C is definitely above normal temp when idling, means higher pressure in cooling system and eventually it will crack expansion tank, as weakest element of cooling system.[/QUOTE]
 

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I don't think it's a thermostat issue. I've you've indeed driven it hard for some time, water temp should've climbed up really fast and way higher than 103 °C with a closed tstat.

Check that non-white smoke out again and be prepared for head gasket replacement (or not, might just be the water pump, or that tstat, or carbon buildup released after some heavy foot at work...) You should try to isolate the problem a little more.
In order to meet eco standards, BMW decided to increase overall engine temperature and made "hot" thermostat controlled by DME, there is heating element which melts wax and therefore opens thermostat quicker and when it is needed, allowing to keep overall engine temperature higher and controlling it within limits. So thermostat doesn't have to stick open or closed to fail, it is enough if heater element doesn't melt wax fast enough for thermostat to react properly or to allow valve to close/ open completely. That is how you get higher temp on idle, that's how you get high temp when drive actively. soft failing thermostat won't drop code and only way to get idea about it's condition is to monitor temperature trough cluster 7 or with diagnostic equipment. 98 C is definitely above normal temp when idling, means higher pressure in cooling system and eventually it will crack expansion tank, as weakest element of cooling system.
 

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I have a similar problem for 2 weeks now.Although I've tried to narrow down the problem with no luck at all. My car 99 323ci overheated while standing still on a road trip, managed to drive it home due to airflow. Cleard the codes and everything seemd fine.To be sure nothing like this happens again I changed the thermostat. And then the fun part begins. I bleed the cooland good! e fan stopped, changed the fan and noticed while engine is at 99degrees outlet temp sensor is at 70. Changed it too (3 times 😬). Gutted my old thermostat so its always open and guess what. No luck! Still the outlet temp was lower from the engine temp like 20 degrees lower somethimes it goes up to 91 while engine is at nearly 100+-. It was almost clear for me so i've changed the waterpump and put my new thermostat again. Bleed the cooland like for the 6th time in a week asuming it was good to rip. It wasnt :(( Only thing left untouched is the radiator but my car runs good temps while on road. It overheats only on idle due to lower temps in the outlet temp sensor. Its like engine is giving and taking the hot coolant when it decides. Did a test for blown head/head gasket,they are okay. Any ideas ?!
 

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I have a similar problem for 2 weeks now.Although I've tried to narrow down the problem with no luck at all. My car 99 323ci overheated while standing still on a road trip, managed to drive it home due to airflow. Cleard the codes and everything seemd fine.To be sure nothing like this happens again I changed the thermostat. And then the fun part begins. I bleed the cooland good! e fan stopped, changed the fan and noticed while engine is at 99degrees outlet temp sensor is at 70. Changed it too (3 times 😬). Gutted my old thermostat so its always open and guess what. No luck! Still the outlet temp was lower from the engine temp like 20 degrees lower somethimes it goes up to 91 while engine is at nearly 100+-. It was almost clear for me so i've changed the waterpump and put my new thermostat again. Bleed the cooland like for the 6th time in a week asuming it was good to rip. It wasnt :(( Only thing left untouched is the radiator but my car runs good temps while on road. It overheats only on idle due to lower temps in the outlet temp sensor. Its like engine is giving and taking the hot coolant when it decides. Did a test for blown head/head gasket,they are okay. Any ideas ?!
[/QUO
Outlet temperature - you mean coolant sensor reading? If yes, then it is all right, lower hose supplies cold coolant to hot engine, engine temp sensor reads temperature of engine, which is always higher than coolant temp.
Does your can has both mechanical fan and aux fan or electric one only?
 

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A few thoughts on all the above:

Cars do run hotter now. (More on that later) Albeit it's not only for reasons of emissions but fuel mileage as well. The hotter the engine, the less fuel it needs. It's only incremental but that's how all of the new cars work.

98°C at idle is a bit high. If your car has an automatic tranny, what's the condition of the fan clutch? Although the DME/Thermostat is quick it's slow compared to the newer cars with the electric water pump. The E46 system is slow compared to those and lets just say it's reactive and not proactive. At idle there isn't much movement of the waterpump/impeller so any change comes about in stages. Engine gets warmer than normal, DME sees it and reacts and opens up the thermostat, then the cooling process begins. Takes a couple of min. If it has a weak fan clutch, it may not keep up.

For sewosb: Weird. Sounds like there is a flow issue IF all of the sensors are reporting correct information? Given you've tried many things, I'd suggest a new coolant temp sensor (cheap enough) on the cylinder head.
Do not run with a gutted thermostat on a straight 6 cyl.
Is the coolant flow from the side into the ET good? If not maybe a restriction? If the flow to the tank from the side (very important!) is not good, the top 2-3 tubes of the radiator will be air bound.
With either case of electric (behind the radiator) fan or fan clutch, if the radiator is as cool as you report neither of the two will help.
Electric fans rely on the temp sensor in the lower hose. If it's cool, the fan does NOT come on. Despite the reported engine temperature.
If a fan clutch and working properly?? The bimetallic strip does not expand and the fan clutch will not lock up. Nor does it need to. The coolant in the radiator is good.
Again you have a engine temp sensor lying and/or a flow issue.

Every time we do coolant work, a lengthy test drive is in order. Cluster unlocked and we watch for verification that the thermostat has opened and the coolant temps are what we expect.
I drove a F30 328iX N26 engine the other day after a water pump/thermostat job. HOLY CHIT, talk about fast and scary temps. Come to a stop and the water pump goes into high speed and the thermostat opens and the electric fan behind the radiator (Primary for BD, LOL) ramps up. Coolant settles in between 95°-98°C. get on the highway at 65-75 MPH and the coolant temp goes between 116°-106°C !! At higher speeds, just like the M54 it drops a little to 102°-105°C (for you'ze folks that er buying these newer N20-N26 cars, the cooling system is super critical IMO)

98°C does not cause coolant tanks to explode per-se. The age of the tank and all of the other plastic bits are the culprit. That's why many here stress the need to change this plastic bits out as a PM.
New cars and or new parts can stand that high of a temperature.

A point & shoot non-contact IR thermometer is a very good friend in trying to sort out cooling system issues. They're cheap enough anymore. Easily ferrets out hot/cool spots and makes diagnosis easier. Has multiple uses and should be a part of any DIY's toolbox anymore. I even have one in the kitchen for cooking, grilling & baking. Indispensable tool.
 

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The engine temp is reading right, due to coolant boiling on me a couple of times. Its a coupe as I said - only electric fan. Its working good. It has to do something with the coolant flowing. I've watched the engine temp in the hidden menu never reached even 97 before
 

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98°C does not cause coolant tanks to explode per-se. The age of the tank and all of the other plastic bits are the culprit. That's why many here stress the need to change this plastic bits out as a PM.
New cars and or new parts can stand that high of a temperature.
98 doesn't, right. But 98 on idle shows something isn't right and therefore load on tank is more than normal, and it is matter of time when plastic fails.
 
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