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Pelican Technical Article:

Replacing the Oil Temperature Sensor

Mike Holloway


30 minutes30 mins






19mm wrench

Applicable Models:

Mercedes-Benz R107 (1972-89)

Parts Required:

Oil temperature sensor

Hot Tip:

Remove any component to provide more room

Performance Gain:

Better idling

Complementary Modification:

Oil and filter change

Before you do any work on your car it is important that you wear safety glasses, work gloves and dispose of all fluids in a safe manner. If you are draining coolant, keep in mind that it is poisonous and should be treated as such. Animals and small children have been known to die from ingesting coolant. If you have to jack up your car, make sure to use jack stands and chock your wheels as well as applying the parking brake. Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability. Always use eye and hand protection.

The Mercedes Benz 450SL is considered by many to be one of the most attractive cars Mercedes produced. It is a stylized combination of power, grace, and comfort and was sold under the model designation R107. At over 3,600 pounds and designed to meet (and actually exceed) strict safety regulations, the 450SL was nicknamed "der Panzerwagen", which means "the armored car", by the engineers who designed it. The 450SL was produced from 1973 through 1980, after which the R107 became known as the 280, 380 and 500 SL.

The SL variant was a two-seat convertible with a standard soft top and optional hardtop and optional folding seats for the rear bench. The designation SL derives from the German Sport Leicht, or Sport Lightweight and was first applied to the infamous gull wing 300SL. The 450SL was the third generation SL. The SLC (C107) derivative was a two-door hardtop coupe with normal rear seats. The SLC is commonly referred to as a 'SL coupe'. This was the first time that Mercedes-Benz had based a coupe on an SL convertible platform rather than on a sedan, replacing the 280 and 300 SE coupé.

The robust, V-8 powered SL is a joy to drive. Many drivers test the power of the 450SL. While the speed off the line is questionable, the top end performs smooth and responsive, giving the driver a sense of security. The 450SL cruises comfortably at speeds in excess of 75 mph.

If you notice that your idle speed is running high with a warm engine, it could be that your oil temperature sensor has failed. There is an easy way to check and see if that is the case. While the car is running in park or neutral, disconnect the plug on the temperature sensor. If idle speed drops below 500 rpm, the oil temperature sensor must be replaced. If the idle speed doesn't drop then the lines may be corroded. If you take an OHM meter and disconnect the plug and check the wire (which will be green and white) and the meter reads 0 OHMS, the wire has been compromised and requires replacement.

The oil sensor can be a very good indicator of what may be occurring in your engine. Upon removal and examination, look to see if there is a layer of varnish on the sensor. Varnish is a product of oxidized oil and can lead to many problems within your engine. Varnish also acts as a thermal insulator, which will provide faulty data.

The oil temperature sensor is located near the oil filter on the passenger side of the forward engine bay.
Figure 1

The oil temperature sensor is located near the oil filter on the passenger side of the forward engine bay.

Here is a picture of the sensor without the terminal hooked up.
Figure 2

Here is a picture of the sensor without the terminal hooked up.

Using a 19mm open-end wrench, loosen and remove the sensor.
Figure 3

Using a 19mm open-end wrench, loosen and remove the sensor.

The sensor is now free and can be replaced.
Figure 4

The sensor is now free and can be replaced. Replacement is the reverse of removal.

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Comments and Suggestions:
Joe d Comments: I recently had a headgasket replacement on 85 380sl. Since then its had a high idle problem. It was up near 1900rpm. I cleaned the idle control valve which got it down to 900. I've replaced the over voltage relay with no luck. The oil temp switch sounds logical but getting a OEM part number is confusing. Can you help
May 22, 2016
  Followup from the Pelican Staff: I would check the engine for vacuum leaks and confirm engine timing is oK. - Nick at Pelican Parts  

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