I have a 1970 Mercedes Benz 250/8 with frozen (closed or open, we’re not sure) heat risers. We’ve been spraying penetrating lubricants like Blaster on them for several days now with no movement at all on them. Any recommendations on how to free the heat risers w/o taking everything apart?
Alternately tapping the ends of the shaft with a soft hammer while ‘jiggling’ the weight might give some success. If the weight is down the valve is likely open and in warm weather you likely won’t notice the lack of heat on the intake.
It seems to me that the owner’s manual of my 1954 Buick that had a heat riser valve said not to use oil but to use graphite. As I remember, if the valve was stuck, one was to gently tap the shaft with a hammer while trying to move the valve. Once free, the graphite was to be used. It’s been a long time since I owned that car and I left the manual with the car when I sold it.
I also remember that the heat riser valve rattled when the car was warming up. It did that one time when it was at the Buick dealer. The mechanic said to bring it in when the heat riser valve didn’t rattle–that meant it was stuck. Rattling heat riser valves were good.
Keep soaking the frozen heat riser with penetrating oil and tap it gently but firmly as you spray. Try to move it gently but firmly with pliers. Repeat.
I’m not familiar with the Mercedes versions, but on other cars they break maybe 20% of the time doing this. Stay patient and just keep soaking, tapping and moving with the pliers.