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Engine coolant temperature sensor, 2005 325

Discussion in 'E46 (1999-2006)' started by Sunbeamer, Sep 19, 2013.

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    Sunbeamer

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    Does anyone know if you can replace the engine coolant temperature sensor without taking the intake manifold off for access? In addition what the resistance should be for this sensor?
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    charlson89

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    Any reason for the replacement?
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    Sunbeamer

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    Engine overheats. It blew the side out of the overflow tank. Luckily it went quick and my wife didn't try to drive it. Less than a mile from home. Added water and made it before it got hot. Serious white smoke from exhaust when I tried starting. I checked the compression. 145 psi in all cylinders. I replaced the water pump, thermostat, and the lower thermostat, which was seriously plugged. Radiator was flushed and is very clean. The amount of dust and dirt between the a/c condensor and the rad was unbelieveable. I thought this alone could have caused it to overheat. I thought the electric fan was at fault. I pulled it out cleaned everything up. Bentley book says it should come on for 20 seconds at startup for diagnotics . It does not. I put it all back together, 3 to 4 miles, it blew the upper rad hose. Tore it all down again. Everything looks good. If run the car for 2 miles, it gets up to indicated normal temperature but the lower rad. hose is not hot. I am wanting to check resistance to determine if the senor is bad, because if undrstand it correctly the sensor controls the electric thermostat and the electric fan. I still want to take it to the shop to get a coolant pressure test. I am trying to drive it though and not tow it there. If the head gasket is blown at a coolant passage it does't show any signs of it. The exhaust is clean it doesnt leak until it she blows.
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    charlson89

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    Is this vehicle manual or automatic? I would have coolant pressure test done for sure to make sure no engine damage was done. The lower radiator hoses has a temp sensor in it that the DME reads to control the electric fan. If you lower radiator hose is not getting hot then your radiator is either plugged or you do not have coolant flow. How are you bleeding the vehicle?
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    Sunbeamer

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    It is an automatic. I pulled the radiator after running a BG rad flush. It flows very well. I pluged the small hole going to the trans cooler and put a garden hose in the high side it flowed with little to no back pressure. Then did the same from the lower to the upper and it of course had a little more back pressure but flowed out the top without indication of any restrictions. I put small mirror in and looked at the end of the alumimum tubes and it is very clean. I am bleeding the vehicle by filling at the overflow tank with the bleeder screw open and the heater on full hot and heater blower motor on low. Once filled I drive it a few miles and then wait for it to cool down. Usually the next day and make sure the indicator bob is the correct height.

    Yes it sure seems the rad is clogged but I checked it twice now and it flows very well.
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    Terry Sayther

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    Stick a fork in it, it's done. Blew the reservoir, blew the upper hose, white smoke. E46 M54 engine with overheating damage is typically headgasket with more damage. Cyl head might cracked, might be ok, but the aluminum block is not tolerant of heat damage. The headbolt threads will pull out unless drilled and tapped for Timesert Thread Inserts---that operation is done with a fixture to guide the drilling. Even then there is risk of further problems. Too much labor for the amount of risk. Best option is a used engine.

    By the way, when we observe a hot engine with a cold lower hose, we automatically assume a problem with low flow due to a sticking thermostat. Cold lower hose=stuck thermostat. Rule of thumb. The thermostat can be stuck due to insufficient bleeding---it will not work with an air bubble inside [air or water vapor will not transfer enough heat to operate the stat.
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    charlson89

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    As Terry said above sounds like you might have a head gasket leaking. I would do a pressure test on the cooling system and see if the pressure and coolant level drops. Also take off the radiator cap with the engine running and watch to see if the coolant is bubbling this would indicate exhaust gases coming into the cooling system.
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    Sunbeamer

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    In reference to the thermostat. Is the engine coolant temperature sensor utilized for opening the thermostat? The Bentley manual is not real clear on exactly how this works. The engine doesnt smoke now. Is simply blows the upper radiator. I will see if it has pressure build up right away.
    Thanks for your help.
    Jerry
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    Terry Sayther

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    Good question----the electric connections to the thermostat operate a heater in the stat that opens the thermostat rapidly for greater cooling. The DME control unit controls that heater and it gets its temp info from the engine coolant temp sensor.

    Look for steam at the first start everyday---sitting overnight with pressure in the system allows coolant to seep into the combustion chamber. Rapid pressure build-up is one thing to look for, you're right about that. If it happens, that's pretty definitive. If it doesn't build up rapidly, it still can be a head/headgasket issue. They make some dye/indicator tools that are designed to detect combustion gasses in the cooling system, but they're not entirely reliable.
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    Sunbeamer

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    The car has 130K on the odometer. I really don't know what happened. Water pump impleller had 0.020" radial play, the thermostat had a paste like substance in it. In fact the whole coolant system had a beige paste in the plastic parts but not on the hoses or metal parts. I have a son turning 16 in February. I will ask him if he wants to buy a used motor and I will help him install it. Last year we did a jet ski togehter. I bought a ski with a locked up motor. It dropped the power valve into to the top of the piston. It took us a few weekends to complete but proved very educational for the lad and was a lot fun this past summer. My guess is we will start the motor search this weekend. Thanks again.
    Jerry
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    Terry Sayther

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    Look at www.car-part.com for used parts including engine. Great project! Good luck--Terry

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