frozen struts

[pdgizwiz]

We had a cold snap here in the northwest last week. The temperatures at dawn were in the high teens and it didn't break the freezing point all week. I drove one of my other cars the first part of the week and took my '97 Previa out on Thursday. Immediately I new something was wrong - it rode like a pallet jack. Every rough spot in the road rocked the whole van and loud thunking had me wondering if the wheels might come off. I drove it a few miles and the condition settled down to the left front, which made a bang whenever that wheel hit anything at all. I could even get it to bang if I jumped on that side of the front bumper.
The only thing that had changed was the weather. The weather was the same the next day, and so was the banging. I knew my struts were old but I thought they'd last the winter. There are no sloppy links or joints.
Saturday it warmed up to the mid-thirties and stayed there. By Sunday the issue had vanished. Back to normal.
I believe that somehow water has replaced at least some of the oil in the strut. When frozen, it can't pass through the orifice that the oil normally does. Guess my struts are in worse shape than I thought. Time to scheme replacement.

[Kurtanius21]

Interesting that would be a problem. Are our struts gas or oil filled? When I drove mine in sub freezing temperatures, it squeeked and rattled, but it still moved up and down. Doesnt makes sense, if yours were really so bad, wouldnt your van be bouncing up and down after every bump when above freezing? Water does evaporate after all. If you do the replacement, you should keep the old parts to do some experimenting on.

[pdgizwiz]

All shock absorbers contain oil. The damping action is produced as the oil is shoved through an orifice in the valve mechanism. Gas filled shocks (and struts) contain pressurized gas over the oil, to keep the oil from foaming. The first thing to go when shocks fail is usually the seal that holds the gas in. The damping mechanism remains so long as the oil doesn't foam up. Eventually the oil itself leaks out and the damping action is lost as well.
I know that my struts are well down this road. There is visible rust on the shaft, so there's no chance of making a gas-tight seal, and there is oil on the outside surface. I've not noticed any bouncing or odd handling so I've been assuming that there is enough oil to provide damping action. There's nothing about my driving habits that would be very demanding on shocks, though.

With the gas seal gone, air passes in and out. In the damp climate I live in, that air contains moisture which will condense into water and fall to the bottom of a reservoir of oil. Exposed to sub-freezing temperatures for long enough, that water will freeze into a chunk of ice. Depending on where that chunk of ice is with respect to the orifice of the dampener mechanism, the stroke of the shock will be limited in range.

If I get a chance once they're replaced I'll drain whatever fluid is in my banging strut and post what I find. Until then, I'll stick by my theory until I have a better one.

[pdgizwiz]

I've got my new struts on today, and drained the fluid out of the old ones.
Water theory is confirmed!
There was more water than oil in the left one. What oil there is is an emulsion. Here's the contents in a bottle - you can clearly see the water in the bottom with the brown water/oil emulsion on top.

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There was more fluid in the right one, and no clear water, but the oil is clearly contaminated.

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