Hello,

I have been reading many threads on the OVP for late 80's - early 90's cars. I can not find a specification for what voltage level will trigger the OVP.

I have a 90 300SEL and, in preparation for some upgrades that include an electric cooling fan, I'm installing a higher output alternator. The unit comes equipped with a voltage regulator set at 14.8V.

I just wanted to double check before I do, that I won't be causing any issues with the OVP.

Thanks for any data/advice.

Kurt

I'm not absolutely sure, but I believe the OVP only supplies voltage to the systems with sensitive solid state electronics like microprocessors such as the "E" part of the KE Jetronic system, ABS system, and SRS.

As long as any alternator's voltage regulator is functioning properly it should maintain system voltage in the 13.5-14.5 volts range for any load as long as that amp load is less than the alternator's max available at the RPM it is turning.

I don't know what you mean by "upgrade", but your car should have at least one OE auxiliary electric fan in addition to the clutch fan. The clutch fan should be fully tightened at 100C and should be much louder at about 2000 revs when it is engaged. You should test it. The aux. electric fan(s) engage high speed at 105C and shut off at about 100C. If the A/C is engaged a pressure switch will energize the fan(s) at low speed as necessary.

My 190E 2.6 has two aux. electric fans. The W124/M103 models have one of larger diameter due to the taller radiator. I'm not sure if the W126/M103 has one or two.

One of my aux. electric fans failed, and I did a failure analysis... posted the results including photos. Search for threads started by me if you are interested in reviewing.

Duke

Hi Duke,

Thanks for the info. Yeah my car has two auxiliary fans in front of the condenser. I live in Southern California and on the hotter days, over 100 F, If I am not traveling fast enough the car starts to run pretty hot. So around town or in stop and go traffic it runs pretty hot and even hotter with the A/C running.

I have twin turbos and a radiator/shroud upgrade planned to handle the extra heat. The fan I am adding has a PWM controlled variable rpm capability and it's brushless for a long service life. Eventually I'm also adding an electric A/C compressor and an electric smog pump. All those goodies need a higher amperage alternator so that is what prompted my question about the OVP.

If no one knows the spec for the breakdown voltage, I'm going to bench test one with a power supply to see how it behaves with increasing voltage input.

Thanks,
Kurt

Do the upgrade, it'll be fine. I did that upgrade to my m103 2.6 and added a 120 amp alternator from the 95 or 96 S500, I have 2 batteries (H8 AGM for electronics, and an H6 for starting the car only), I had the 600 watt fan from the w203 also (I have since taken the fan off because car temp ran too low). But I have the 2 aux fans now with no viscous clutch fan and I too am in socal (desert area) and the way I have the fans set up, the temp rarely goes passed 100, even in the summer with ac on. I run a 79C thermostat in the summer, but keep everything else the same.

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1990 190E 3.0L

Ismalley,

It sounds like you have done some similar things to your vehicle. What voltage does your upgraded regulator put out?

Thanks,
Kurt

All modern car regulators keep the voltage between 13.5 and 14.5 volts. Something in my alternator recently failed and the battery light, abs light kept staying on. When I checked the voltage the car was at like 15.3v so I just replaced the alternator weeks ago. All is fine now. I've added a ton of extra options to my car that's why I beefed up the electrical system. Currently working on adding something else. As soon as I finish designing everything and testing it I'll post it so others can add it if they choose.

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1990 190E 3.0L