Inverter Coolant - big leak, emptied overnight

2011 Prius, 110K miles. I last checked all fluids early Sep - everything was good.

Yesterday, while driving back home, the Yellow Triangle popped up with the "Check Hybrid System" message. I drove for about 15 minutes after the message to reach home. Checked for codes and it showed "P0C73".

Started with the basic checks and popped open the hood to find that the inverter coolant tank near empty. Not at "L", it was almost empty (The engine coolant level is fine and is exactly where it was last month). I could barely see some pink fluid at the very bottom of the tank. A leak for sure.

It was dark, so couldn't work on it. Topped it up and checked before bed and the tank was already at half, and there was a puddle next to the tire behind the front bumper (passenger side). On shining a light under the car, I could see liquid dripping from plastic cover. I also noticed that some liquid is dripping from on the outside of the radiator when I shined the light through the front bumper. Checked this morning and it is empty again.

No recent work was done on the engine. I changed the 12v battery last month, but I don't think that matters here. I hit a speed bump pretty bad in a parking lot a couple of weeks ago, heard a loud "thunk". I checked under the car after that and didn't notice any obvious damage, and the car drove fine for two weeks. Didn't notice any fluids or stains on the driveway where the car is parked daily.

I am hoping it is just a loose drain plug. I have it up on Rhino ramps now and am going to take of the cover and inspect. What else should I be looking for? Are there any other common points of failure?

Thanks.

 

Thanks for the reply.

Everything underneath looks fine. The drain plug is intact and no sign of leaks there or any where in that area.

All the leak seems to be from the radiator, towards the passenger side. I am off to get some distilled water so that I can fill the coolant tank and find the source of the leak. Can I add a drop or two of food coloring or fountain pen ink to color the water? Maybe a cup of the coolant to give it color is safer.

Was rotating the tires on my other car (Mazda CX9) and found two stripped lug nuts. One wouldn't budge and broke off completely when I applied force. Now I got to replace two wheel studs on it. Just not my day

 

Topped up with distilled water and the leak started within a few minutes (didn't start the car). Seems to be coming from the front of the radiator. Heard a sucking sound, so removed the trip piece to the front of the engine bay to have a better look at the front of the radiator. I could see bubbles forming and that was the source of the sucking sound.

Is it okay to start the engine and confirm the source of the leak? Water will probably shoot out once the pump turns on.

So, I am guessing I got a hole or crack in the radiator. What is the fix? Straight replacement, or can it be repaired?

 

Started the car for a couple of minutes, and sure enough there was a steady jet from the hole. Car is out of commission till it is fixed.

Oh man, that is expensive. Ebay has a few used ones, but I don't want to risk it with pre-owned.
Best price I could find - Amayama has it for about $200 shipped from UAE - Buy Genuine Toyota G901047032 (G9010-47032) Radiator Assy for Toyota Prius. Prices, fast shipping, weight - Amayama

Also looking at non-OEM parts from RockAuto:
DORMAN 918903 for $37 (plus shipping) - More Information for DORMAN 918903
TYC 13124 for $51 (plus shipping) - More Information for TYC 13124
Amazon also has the Dorman for $53 shipped -

Any opinions/experience with either of them?

As for the coolant dilution, I will anyway drain it all to remove the cooler. So most of it would be out I think. If required, I will get one of those vacuum purge kits to suck any remaining coolant from the inverter & pump.

Yes, that is exactly what I think happened. A bit of a pain to replace the inverter cooler. Still debating whether to DIY it or to find a local shop to do it. Thanks for the tip about the mesh. If I DIY the job, then will add the mesh.

 

UPDATE:

Replaced the inverter cooler with an after market item from Amazon. About $50 shipped, delivered in 4 days.

I received a "Platinum PRO" brand item, with Part No. INV13124 and "Made in Taiwan". Seems to be of good quality, well made. Couldn't find any difference between it and the OEM one I replaced.

Steps:
- Remove front bumper (followed this video -

)
- Loosen the frame bracket on top of the radiator assembly (referred to the shop manual and some of this video -

)
- Remove four bolts (two on each end) and remove three braces (one connecting to the inverter and two to the radiator assembly). And the top bracket is now free to move a bit. Didn't want to remove it completely as it would mean disengaging the hood-release cable. Just lifted it a bit out of the way to gain access to the radiator bolts underneath.
- Remove two bolts on the top of the radiator assembly (one on each end) to remove the top plastic cover.
- Then removed four bolts to remove the inverter cooler (referred to the shop manual). Two facing front on the driver side, and two facing side-ways on the passenger side. Then disconnect the two coolant tubes on either side of the cooler.
- A bit of coolant came out, had a plastic tub to catch the spill.
- Drained the inverter coolant completely from the bottom.
- Cleaned up all the mess made by the leak. Used a hand pump to blow air through the now open coolant pipes and a bit more coolant drained out.
- Installed the new inverter cooler. One thing I missed were two rubber bushes that go on the top posts of the cooler. They help get a snug fit inside the plastic cover. I missed them and didn't remove from the old cooler. Then wondered why my new one was not snug in place and jostling around a bit. Once I figured it out and got the bushes in place, it was a nice snug fit.
- Assemble everything back in reverse process. I referred to the shop manual to make sure all the bolts were torqued to the appropriate value. Used a 3/8" Harbor Freight torque wrench.
- Used a cheap coolant vacuum refill kit to test. It held -20 for a couple minutes and I was satisfied that there were no leaks. Used the kit to suck coolant from the jug, but it only took about 2 quarts before that needle came to zero and it stopped sucking. I added the remaining (about another quart) normally for it to reach "F".
- While at it, I also replaced the engine coolant and the ATF.

Note: Before re-installing the bumper, I took all your advice and added the wire mesh to the grill openings. I got a 3-ft Gutter Guard from Lowes for about $3 - https://www.lowes.com/pd/Amerimax-Lock-in-Gutter-Guard-Black/1000979076

It has 1/4-inch mesh, with a nice black powder-coat finish. Blended perfectly into the grill. Once piece was enough for all three openings. The bottom big opening took an almost rectangular (trapezoid) piece - 4.5" tall, 26.5" wide at top and 28" wide at bottom. It was easy to cut the mesh with a pair of tin snips. For the two smaller openings, I started with a 2.5" x 12" rectangular piece and trimmed to shape with tin snips.

Then got some black zip ties and secured the mesh to the grill. At a couple of spots (at the edges of the grills), I couldn't find a opening to thread the zip ties through, so I just drilled a small hole into the black plastic and used that as an anchor for the zip tie.

All-in-all, it turned out great. Not bad at all for a weekend's work.

Car drives nice and smooth. Put about 100 miles since then, and the coolant levels are steady. Glad to have some major maintenance done (car is just over 111K miles). Just need to replace the Spark Plugs and flush the brake fluid and I'll be done with all major maintenance.

THANKS FOR ALL YOUR HELP!!
Saved a few $$s, improved my Prius and learnt something - all at the same time