pH testing coolant.

Yes, the coolant turns acidic as it ages, hence a lower pH reading.

 

congrats on your new wheels!

 

Read post #11
Fluids | PriusChat
Most likely the inverter coolant was NOT drained/filled. Financial disincentives to do so.

 

Does the coolant in the reservoir cycle in normal use ?

 

Just speculating: say the fluid level goes up/down maybe 1/4" due to temperature expansion. That's enough to keep the fluid roughly homogenized, albeit with a bit of a lag.

I think the coolant in the reservoir circulates, albeit with some reluctance.

 

Then you think the pH differences OP found are an artefact?

I did pH testing a few months ago with similar results to OP:

#20

As promised, pH testing:

1. Coolant from Inverter Reservoir, ~ 50k miles use
2. New Asian Zerex Coolant
   
3. Ruby Red Grape-fruit Juice

The strips are "URS-6L," made by teco diagnostics as a urine dipstick. The pH test is the second from the top and ranges from pH 5.0 on the far left to pH 8.5 on the far right. The test relies on color change of bromothymol blue and methyl red to pH. This is a variant of the 'universal indicator' method.

Conclusions:

1. Ruby Red Grapefruit juice is safe to drink, at least pH wise. The color change took time, so we are not reading the color of the juice. The strip appears to be working.
2. New Asian Zerex Coolant is alkaline
3. Used SLLC is slightly alkaline. Time to replace ? I think so.

View attachment 71135 View attachment 71136 View attachment 71137

 

and that's why you need to change it cause acid will eat up all the alloy in your cooling system. if your not gonna diy, just wait to your next service interval, no need for a special trip since its still alkaline

 

Bumping this thread as it is good a place to post this as a new one.

Today I checked the pH and DC voltage to ground for the ICE coolant, inverter coolant, and brake fluid. In each case a few drops of the fluid were removed with a clean (actually sterile plastic oral) syringe and put on pH paper. For the DC voltage the positive probe was wiped clean with a dry paper towel and dipped in the reservoir about 1 cm with the negative probe placed on a clean bolt. The brake fluid cover and surrounding area were wiped clean and allowed to dry before it was opened.

Inverter coolant: pH 8.5, 147mV
ICE coolant: pH 8.0 or 8.25, 39 mV
Brake fluid: pH 6 (???), <25 mV

For the coolant the mV started lower and slowly went up. When it stopped increasing the value was called. Not sure why this happens, it could be that the fluid reacts with the probe. It didn't matter which ground point was used for the negative probe. Odd that the loop with the slightly lower pH had the lower voltage. If the voltage was resulting from corrosion I would have guessed it would have been the higher voltage.

I think the pH value for the brake fluid was meaningless - the pH paper didn't change color, it just got wet. I think it was just what happens when oil is placed on it. The voltage in this case started at 25mV and fell steadily, the opposite of the coolant. When it got to 16 mV I gave up since it didn't seem like a good idea to leave that reservoir open for very long.

Broke one clip removing the front tray. Another popped out and performed a delightful little dive as if off a spring board, up and then down into the space between the motor and the inverter, where it disappeared, probably never to be seen again. I don't think anything moves in that region, and I made sure it didn't ricochet to near the moving parts on the throttle body. It didn't fall out the bottom, hopefully it shakes through and out at some point.