My 2004 just developed a coolant leak. The past couple times I've moved the car, there's been a small pink puddle under where the engine was. The leak seems to be coming from a weep hole positioned between the two bolts of the lower engine mount. The hole is circled in red in both pics. Any ideas what the problem could be? This looks like it will require removing the engine from the car and taking it apart to reseal something. This is more than I can do myself, but I want to go into the dealer as informed as I can be. Thanks!
I suggest you check the coolant level in the inverter coolant tank, as well as the coolant level in the engine radiator overflow tank and the engine radiator itself (need to remove the large black plastic cover over the radiator for access to the radiator cap.) If that does not provide a clue about the coolant leak (engine vs. inverter/transaxle) then you might want to look at the engine head for a leak. You may have to raise up the front of the car so you can get under the engine and look at the side of the engine facing the firewall. It is possible that the leak is coming from the transaxle instead of the engine. Note the transaxle coolant drain plug is the 24 mm hex plug a few inches to the right of the leak area. Also, look at the inverter to see whether any pink stains from dried coolant might be visible. If you don't see an obvious source of the leak, then it would be quite reasonable to seek professional help. It is possible that you may have a cracked component causing the coolant leak, as there is no reason for coolant to be present at the seam between the engine and transaxle.
Hello, Tupelo, Did you get a confirmation of the source of your coolant leak? I just found the exact same leak between the motor mounts of my 2004 prius, with low amount of coolant in the invertor reservoir. Please let me know what the problem was - it will save me a lot of searching - thank you!
That's a tough fix if tightening the bolts don't work. It's a rare report a leak there. Try tightening the bolts and if a high mileage car just keep filling the inverter because the engine and trans have to come out and the leak repaired and that will be expensive.. If a high mileage car best to just replace the engine trans assy with a lower mileage junk yard motor.
Try to make sure that it’s actually leaking from the hole and not just leaking somewhere else and migrating from the outside of transaxle. There are many potentially leaking places above that shouldn’t be hard to repair. If it’s actually leaking from that hole you need to remove the transaxle. You can remove the transaxle without removing the engine: DIY: How to remove GenII Transmission | PriusChat
I'm going to revive this ancient thread because my 2009 Prius just developed a leak in the exact same location. I can confirm it is coolant and the coolant is coming from the electronics/inverter loop. I added UV dye to only that loop (thus the bright green color in the pictures). I'm thinking that there must be an internal seal or gasket causing this, but wanted to see if anyone who had the problem previously had diagnosis. 20250615_180818(1) by thejaycan posted Jun 15, 2025 at 11:39 PM 20250615_181405(1) by thejaycan posted Jun 15, 2025 at 11:39 PM
I’m no expert. First time Prius owner and haven’t kept up any maintenance except oil changes and a onetime inverter/radiator coolant change at 100,000 miles.Then I read after this supposed to change at 50,000. I’m past due at 167,000 miles. So I called to check on doing it again and he told me I could go till odo at 200,000 miles. Well nothing on internet nor this chat forum supports that. But I said I wanted original Toyota coolant. He told me when he did mine he did not use Toyota coolant. I almost fainted, It’s probably ok but it’s best to pay extra and use only Toyota dealer brand coolant because aluminum engines and silicone gadgets degrade if wrong coolant is used and replacing the inverter and other expensive parts because of leaks is real expensive. I did Google the brand he said he used. It seems on manufacture label that it is acceptable. But it’s not good to top it off when low with another brand of coolant. Well when I get oil changes Im sure if it needs it toyota tops it off with their brand. Mixing formulas of different brands should not be done. The one he used is close enough that perhaps it doesn’t matter. I’m going to insist next time he use Toyota brand unless for some reason it’s a million dollars. I’ve driven it 67k miles with what he used and no issues so far and hope he hasn’t lessened the life of my car. So either your leak is from wrong coolant formula or mixing formulas or it wasn’t changed often enough. If use the wrong coolant formula even it it’s the right color it degrades gaskets, causes rust and corrosion and can turn to a jelly like substance and clog all the ports. If the inverter box leaks probably have to replace it. If it’s clogged up or suffering degradation and corrosion then there may be other components in that system corroded as well. The same solution is used in the inverter and combustion engine so it all could have issues. Only other thing could be something else causing overheating. So not only does it have to have the same coolant as what Toyota original coolant is but it has to have the same anti corrosion chemicals added to it. So those inert ingredients on coolant matter big time. I hope you can get it repaired and then do a complete flush to get all coolant out and refill it and do the inverter and the coolant. because if the wrong thing was used in one of them chances are they used the wrong thing in the other as the same coolant goes in both. I’m just finding this out as of today and need to redo my own car. Thank goodness it’s not leaking yet and the product they put in mine was decent enough for my make of car. Also OEM does not mean original equipment on a coolant bottle in the same way a car part is oem. On coolant it just means it is compatable with Toyota brand but it is not the same formula.
