2016 Prius II cabin heating problem

Hello all,
The last couple days we had a cold snap in Ohio. Yesterday, I noticed my cabin is not warming up as usual. Today, I research a little and found This Thread about a recall including my model regarding the heat exchanger within the exhaust. Although I do not have loss of radiator fluid, I have many of symptoms reported by others on the thread. So I thought I'd post for input from others before implementing the work around on pages 2-3 of that thread.

I did a little investigating. Normally the Prius warms up within 10 minutes, even on the coldest days, whereas the past 2 days it is about 33F at the time I drove it, not really cold for such a slow warm up. I check the fluid level in my radiator reservoir on the right side of the radiator,, it was down only slightly from, just below the "low" line which is on the right side as one faces the engine compartment. The other reservoir, on the left, I assume is overflow, is empty as far a I can tell. I added a small amount of radiator fluid , maybe 5 ounces to bring it up to the "Full" mark.

I drove the car in stop and go traffic for 25-30 minutes before feeling warm air come from the floor vents with the control set on "HI". Then I kept checking the vent by feeling it and noticed that when the ICE was running, I would get warm air shortly after it started and when in EV mode, it would return to cold in a few moments after the switch., at 35 minutes I parked the Prius for 90 minutes and returned home with a 10 minute drive. Same this happened: I drove it up to 55 mph, the ICE engaged warm air again, back in town, at stop lights and EV mode cold air again. I turned on the front defroster for a minute, it was also blowing cold air on the windshield. Any comment would be appreciated. The car has no service problems previously of any kind and currently has 187,300 miles.with a lifetime MPG of 62. I don't notice a change in MPG yet as the problem is new.

 

Thanks. I want to see if I have any codes or errors. There are no trouble lights displayed currently.

 

I checked fluids again, added about 1/2 quarts of engine coolant and now everythings back to normal as far as I can tell.

 

yes, the problem is I hadn't really checked the engine coolant level for almost 9 years. I did top it off, but plan on changing both coolants soon, probably tomorrow.

 

it does help, thanks.

 

Thanks, MrFixer, I found the radiator reservoir tank empty and topped it up with prestone for asian cars cooling fluid and a couple days later drained and filled with toyota cooling fluid. After driving it for a couple days now, I am seeing no reduction in volume in the reservoir. Since I had not changed or topped up the fluid in almost nine years, it was just low due to evaporation, or a leak so slow, it makes no noticeable change to performance. When I topped it up with the prestone, it was less than 1/2 gallon, and my heater was working again immediately.