Constantly Overflowing Coolant

The cooling fan should turn on any time the A/C is ran. This is common on most all cars. There is temperature sensor somewhere that turns it on either directly or turned on by the cars computer. Try turning the A/C on and go from there. It is difficult to get trapped air out of the Gen 2 Prius.

The engine temp sensor should be on the cylinder head and a couple of relays turn them on, check for blown fuses.

 

Besides problem related to fans it could also be a bad thermostat or faulty coolant pump (or something else). But the system just shouldn’t be this hard to diagnose. You just need to take it to a place where they know what they’re doing.

What you can do is monitor the coolant temperature from OBD2 from cold start to see how temperature rises when the engine heats up. From that you should be able to tell if it’s bad sensor (or something related to it), bad water pump (have not heard this happening with a Prius) or bad thermostat/air in cooling system.

 

Is your radiator cap working properly?

 

I would talk to Toyota corporate about their response, and try another dealership.

 

Did this problem start out of nowhere? Had you opened up the cooling system for any reason prior this issue popping up?





iPhone

 

Would it be fair to say this is not just "according to the dealer scantool" but in fact "according to the dealer", reporting back what they did with their scantool?

If so, there is an extra layer of interpretation in between that scantool and us. They might be doing a perfectly fine job on the interpretation. But when there's a picture that doesn't seem to make sense, it can help to list off all the places where something could be getting overlooked.

-Chap

 

What does "boiling over" mean? Were you able to demonstrate this problem to the dealer service writer or the technician?

How do you know that the engine is overheating?

What does it mean that the coolant is spewing all over the place? Is there a leak in the system, or does this happen only when you open the radiator cap?

Do the radiator fans operate when the air conditioner compressor is running?

There seems to be a large communication gap since you are told that everything is working properly, yet you believe that a problem persists.

 

Not sure about prius but if there is a hole in the overflow tube from the radior to the coolant overflow tank it will draw air back into the system. Replace the overflow tube with fresh tubing.
Normally if there is coolant in the overflow tank the radiator will be full. If not there is a hole someplace in that overflow tubing. usually they crack right where they are clamped.

 

1) If the engine were overheating, the thermometer looking warning lamp would be on. That was not indicated, so we can rule out overheating.

2) Both the dealer and kaputi agree that there are no combustion gasses in the cooling system, so we can eliminate internal causes.

3) There should be a free flow of coolant between the ENGINE radiator and the overflow bottle with the radiator cap and overflow bottle cover removed. Verify this before doing anything else.

4) We are talking about the ENGINE cooling system and not the HSD cooling system, right?

Finally, getting all the air out of these can be a chore, especially for those who do not repair vehicles for a living and honestly even for some that do.

 

Has your thermostat been replaced before?

Pretty sure mine runs steady at 185F (might've been up to 193F in AZ or Texas, or so said the Torque app), otherwise the fan comes on until it cools back down to 185F.

One time the belt came off and Torque gave me a warning that the coolant was over 200F (had set an audible warning for 200F), a couple of seconds later the dash lit up like a xmas tree. Not sure at what temp the dash goes crazy, might be at 212F give or take.

 

Are you the original owner, and how many miles?

When did you first notice this problem and under what scenario?

Do you have a android phone, a OBD2 blue tooth adapter and a copy of Torque?

If so, follow the advice valde3 offered in post #3 above. You need to watch the engine warm up and know at what temperature the fan turns on.

Did you check if the radiator fan comes on with the AC? (like padroo in post #2, and Patrick in post #9 suggested)

Your thermostat should be open well before 200F, and the fan should also be turning on before reaching that temperature. Maybe the factory mechanics missed something, or was it the service tech that gave the numbers you mentioned above?

If the vehicle overheats, there should lights on the dash.

How are you going about purging the air from the coolant system?

 

When did you first notice this overheating problem?

If this vehicle has 200k on it, has the water pump ever been changed?

Have you noticed any weepage around the water pump shaft, or pink snot in that area?

If the fan isn't running continuously after the engine reaches (above) a certain temperature, most likely you have a bad fan or fan switch.

What kind of problems did you have getting your mini-vci cable and techstream working?

 

If true, this can only mean that the amount of compressible (gaseous) material inside the system has increased since the last time you had the cap off and corrected the level.

If that was checked for, it may need to be checked again with more care.

-Chap

 

Glad to hear things are working again.

OBD2 bluetooth adapters cost about $3 and up (with free delivery from china), and will make it easier to monitor various things in real time.

Check your PM for help with the mini-vci cable setup, you will need to get this working to be able to read various DTC/INF's.

 

What Blue Devil product did you use exactly? They have a bunch for cooling systems.

-Chap