Changing engine coolant

The two things with coolant replacement that get you are air pockets and foaming. Air pockets are really bad as the car may overheat or as alot of posts listed here complain about will drive you nuts with all the water running sounds through the dash. You need this tool or something like it to change the coolant and inverter coolant correctly:

MTY MV4535 Mityvac MV4535 Cooling System Air Evacuation Kit


Careful on the inverter coolant because if you have air pockets you will never know it until it throws a DTC that the inverter is overheating which in most cases is too late.
In either case I would include this product into both the radiator & inverter coolant tank as its main function is to stop coolant foaming and decrease surface tension and its excellent anti-corrosion protection. It really works well. I use it in my 07. Here's an excellent coolant white paper:

http://www.redlineoil.com/whitePaper/21.pdf

 

I had the opportunity to change the engine coolant on smtrader's 2004 Prius with 80K miles today. A very fine gentleman; he came down from Los Angeles to visit me in south OC and did a substantial portion of the wrenching himself.

We first checked his tires, brakes, and suspension while waiting for the drivetrain to cool down after his extended drive. All appeared good except that the rear shocks had some oil seepage. The front brake pads and rear brake shoes looked quite good, plenty of lining. The front discs were clean, the rear wheel brake cylinders were not leaking fluid, and all flexible brake lines looked good.

Next we replaced the transaxle fluid for the first time on his vehicle, no issues.

Then we got around to draining the engine coolant. This required removing the left-side engine under cover and partially removing the left-front fender liner to access the coolant heat storage container. We started by draining the coolant container, and as expected, that fluid was quite hot. Then we opened the radiator drain, but no fluid came out. Finally we opened the engine block drain and a tiny amount of coolant came out. The old coolant looked quite good, no debris to speak of. We used a vinyl hose to route the drained coolant into a drain pan.

Hence, my first conclusion is that opening just the coolant container drain will allow you to drain ~95% of the coolant that will come out by opening all three drains.

smtrader wanted to replace the engine thermostat. That turned out to be relatively difficult because the metal compression clamp on the hose leading to the thermostat cover was shaped in such a way so that it could be opened up only a limited amount. So we could not remove the hose from the thermostat cover and had to attack the two nuts securing the cover, from the top as well as from the bottom. We eventually got the thermostat cover out and removed the old thermostat. It visually looked fine. More coolant came out of the engine at this point, perhaps 1/2 quart or so. Some dirt also appeared in that drained coolant, perhaps it was from the outside of the thermostat cover.

Then we installed the new thermostat. smtrader had purchased a thermostat and gasket from a discount auto parts store as well as from his Toyota dealer. We used the Toyota thermostat. The rubber gasket runs around the outside circumference of the thermostat. The aftermarket gasket had a tiny ridge along the outside edge, while the Toyota gasket was smooth. Who knows if that might result in a leak...So we used the Toyota gasket.

My second conclusion is that I would advise that owners remain with Toyota-branded parts to avoid issues like this.

The total amount of coolant drained was ~6 quarts, so two gallons of SLLC should be enough for this job. The rated system capacity is ~9 quarts.

It was very slow work to refill the coolant. For a while, I forgot about the valve at the left-side top of the radiator that allows air to vent when coolant is added. After I remembered to open the valve (using a 6 mm Allen key), then work went smoother. However you must be careful not to allow coolant to spill out of that valve.

I removed the CHS relay that lives in the relay box mounted to the cowl. If you gently pry out that relay, you will note a pair of copper terminals and a pair of silver terminals. The silver terminals are for the relay coil while the copper terminals are the switched terminals. Hence I used a small paper clip to bridge the relay socket terminals that would mate with the copper terminals, to run the CHS pump. It was not obvious that running the pump helped that much to promote refilling of the system. However I ran the pump intermittently while smtrader continued to add coolant.

After around 3 quarts of fluid had been added, I started the engine and used inspection mode to keep the engine running and allow the thermostat to open. I also set the cabin air temp to maximum heat to allow the cabin air heater to fill up with coolant.

Hence my third conclusion is that Ed's suggestion to use a vacuum assist tool may well save substantial time in the refilling process.

In any event, we finally used around 6 quarts of coolant in refilling the engine coolant system (although some portion spilled on the ground), and smtrader felt comfortable that his car would survive the return trip home.

We reinstalled the left side engine under cover and the left front fender liner. Regarding the under cover, one of the plastic fasteners that secures it to the left front wheel well was impossible to remove. The associated hole is square, and the fastener has ridges that lock it into the hole. We were unsuccessful in removing the fastener, so the engine under cover was reinstalled on top of the fastener head rather than being held in place by that fastener. There are sufficient other fasteners so that there is no concern about the under cover coming loose.

Any suggestions about how to remove that plastic fastener which fits into a square hole?

I hope that smtrader made it home without incident, and will provide his perspective on our car clinic today.

 

Thanks for the description of changing the engine coolant, very interesting! A few questions, if you don't mind:

How much trouble, if any, did you have with getting out the air pockets in the system?

Why was the inverter coolant not changed at the same time? Simply run out of time to do it?

Thanks,

Rumple

 

Hi Rumple,

Lots of trouble, this is why it took a long time to replenish 6 quarts. You just have to be patient and keep at it until you've added the amount of fluid that you had previously drained - so leave plenty of time for this project...

I've provided smtrader with repair manual info about the inverter coolant, so he can decide if/when he wants to tackle that job.

 

Patrick,

Sounds like using a Mityvac might help pull air out of the system--although I've never tried that. I'm surprised the pump didn't do more to help fill the system, but glad to hear it worked when you jumpered the relay. Since I'm not interested in replacing the thermostat, I may circulate some distilled water to clean out all of the old coolant. Any better ideas?

 

Hi Rob,

Assuming that you plan to use SLLC, I do not think that using distilled water as a flush is a good idea for a couple of reasons:

1. The capacity of the system is 9 quarts but we were only able to drain ~6 quarts after opening up all three drain cocks. Hence if you introduce distilled water into the system and do a thorough job of removing all of the old coolant, you will end up with 3 quarts of water plus 6 quarts of new SLLC which is 50% antifreeze / 50% water. The bottom line is that you will have 6 quarts of water and 3 quarts of antifreeze, for a 33% blend. This is insufficient for freeze and rust protection.

2. The old coolant when drained looked very clean, no debris. (The coolant that drained after we removed the thermostat may have been contaminated with dirt from the exterior of the engine.) So I do not think it would be harmful to have it remain in the system, being mixed with new coolant in a 1/3 - 2/3 ratio.

 

Good job Patrick. Thats a lot of work. Replacing the thermostat was good. But thats where the air pockets get you. You obviously were fighting air which is why it took so long. But, not having a vac I would have let the car run a while with the rad un-capped with the heat on. Did you hook up your scan gauge to check on op temp? Also I would have included some anti-corrosion inhibitor. Aluminum corrodes mightily. 50/50 mix does not have enough anti-corrosion properties to it. (See Redline White paper above)
Also as a side note btw, imho anyone changing out the inverter coolant without a vac is inviting disaster. The inverter is the heart and workhorse of this car and runs very hot. That coolant must be air pocket free.

 

The vac doesn't help. It does the job.

You can usually just dump the rad only with no problem. Dump the rad. Fill with distilled water. Run up to op temp. Dump again and then fill with 100% anti-freeze. Clean out the over flow tank. That will help alot. When you pull the thermostat it gets alot of air in the system. Without a vac you will usually have a gurgling dashboard. You have a scangauge for temp check yes?

 

Hi Ed,

Yes, we ran the engine in inspection mode for a long time with the radiator cap off, adding fluid whenever the level dropped down.

I agree that the Mityvac tool that you cited in post #21 would help, assuming that you have available a source of compressed air at home. However at $119 the price is relatively high for a DIYer who might do this job only once in the life of his/her Prius. So, a reasonable alternative is to do the job without the tool and plan to spend much more time at it.

Regarding the inverter/transaxle coolant loop, I've drained and replaced that system on my 2001 a couple of times without using special tools. However the 2001 has two bleed ports compared to the 2004 with one bleed port. Not sure whether this means the 2004 will be easier or more difficult...

For those who decide to tackle the inverter coolant system: before you do anything, note how the inverter coolant pump sounds when the car is READY and the gasoline engine is off. Also note the appearance of the fluid in the container where there is a step in the level.

When working on refilling the inverter coolant and getting air out of the system, it may help to take a short drive (like around the block) if you don't seem to make progress. I'm not sure why this should be, since the pump is electric and operates at a fixed speed. Maybe as the system heats up, that helps to purge out some of the air?

You have to keep working on refilling the system until the pump sounds the same (no air) and you see the same step in the level of the fluid. That visual and aural check offers sufficient proof that the system is circulating coolant.

The final proof is when you take the car for an extended drive in the summer heat, and no warning lights appear!

 

Is it necessary to use the powered Mityvac vacuum tool, or would the manual Mityvac pump do the same job, albeit more slowly? I also happen to have a large vacuum pump, which I might be able to use with the addition of a reservoir or something to catch the coolant.

I'd like to get all of the old coolant out, since it has a green tinge (someone evidently added the wrong coolant), but will be replacing it with the premixed SLLC, which is already a 50/50 mix. However, if I purge the system with distilled water, I could easily end up with 40/60 or worse, yes? Is it conceivable that one could operate the Prius' pump during the draining process, to move otherwise inaccessible coolant back into the reservoir for subsequent draining? Or might it be getting trapped somewhere else, like the heater core?

Fortunately, the inverter coolant is fine, so I won't be touching that for a long time, I hope.

 

Hi Rob,

Yes, the heater core is the likely place that the coolant is trapped, since an electric pump is in that loop. If you can find the relay that controls that pump, maybe you can run the pump while draining the system to get more coolant out.

You'd have to study the wiring diagram to see whether 12V is available at the relay terminals when the car is off. If not, then you might use a lab power supply or a couple of 6V lantern batteries in series to provide the necessary power to the correct relay terminal and to ground.

Conventional cars have a heater valve to control the flow of coolant into the heater core. I haven't studied how 2G controls this, and to what extent the valve is open or closed when the car is IG-OFF. That could be another reason why the heater core is holding old coolant within.

My estimate is that if you use distilled water to purge the system and refill with SLLC, then you will end up with 33% antifreeze/67% water unless you are more successful in draining the water/old coolant than we were.

 

Hi Rob,

Please see post #9 from the following string:
http://priuschat.com/forums/care-maintenance-troubleshooting/51528-what-does-mean.html

The OP asserts that he was able to purchase undiluted SLLC. Perhaps you may wish to inquire into the availability and pricing of this, so that you can feel comfortable using water to purge out the old coolant.

I bought diluted SLLC earlier this year for $21/gallon from Tustin Toyota, a local dealer in OC, while smtrader paid $23 at a Los Angeles dealer. If you are able to locate undiluted SLLC, please let us know its price.

 

Patrick,

The dealer tells me SLLC is ONLY available as pre-mixed. He said that the red coolant, which comes in concentrated form, is different stuff. Perhaps that's what this individual was working with. They're evidently compatible, though, so probably no great harm done. I'll probably have to waste a little coolant to end up with a fairly pure solution. The good news is that they're currently selling it for $16.95, but won't have any more for a couple of days. I already have two gallons. Maybe I'll need to get two more, but I sure hate to waste it.

 

Thanks for the recycling suggestion. I've read that coolant never wears out, except with respect to some of the anti-corrosion additives, which can actually be replaced.

 

I changed my prius engine coolant this last holiday weekend, several important points to remember, most importantly even after the heater core is working (running hot)do not assume the system is purged of air, recheck/add to radiator after the next shut down, not just check the overflow container. Also , running the engine at higher rpm's helped open a shut thermostat-probably by pressuring the system, disrupting air pockets.

Around 4 run cycles (over 4 days) were needed to refill car with coolant.

I have an assumption that I could refill the drained engine antifreeze/coolant without a vacuum tool or special scan tool, that simply cycling the engine over time will eventually work all the air out of the system. I did have the scan gauge to monitor the engine coolant temperature which did prove valuable.

I drained the coolant using the valve on the radiator and the valve on the coolant thermos. I did not see the engine coolant valve.#
I tried to take off the lower radiator hose, but couldn't. Simply squeezing this lower hose after draining led me to believe it was fairly well drained. I was able to take off the heater hose and blowing threw it, helped to drain the heater core.
I considered flushing with water, but the coolant looked fairly good, and the replacement is only 50/50 so didn't. I was able to change over 1.5 gallons of coolant.
I had the three day weekend off, so I opened / drained the coolant system about 12 hours after turning off the motor from an all day mail route drive. I was surprised the coolant was only warm coming out of the thermos tap. Adding the coolant was like any other I had done, first with engine off, pouring into the radiator, then engine running, adding more. Squeezing the upper radiator hose helped bring down the level to add more. I would eventually cap the radiator, then keep running the engine till it got up to operating temp, monitoring the scan gauge coolant temp.
Then I would simply turn it off and wait > 12 hours or the next day. I would re-add coolant to the radiator and reservoir and simply make a short drive around town. The third drive, I was able to get heat out of the system, and assumed the system was pretty well flushed. I was using a partial full coolant jug up from my previous inverter coolant change, and so didn't keep an accurate measurement, which I will next time. The fourth day, a work morning, I checked the reservoir and the fluid hadn't gone down. I don't think I checked the radiator. Driving to work on a 4 lane highway, my coolant temp started climbing, I realized the thermostat wasn't opening. I slowed down, and the temp went down , but not enough. I stopped, and saw the reservoir was fine. Drove again, same thing, temp climbed to 225 F -not good. I pulled over and quickly touched both of the radiator hoses, top was definitely hotter then the bottom, showing a closed thermostat. I slowly, with a rag, opened the radiator cap , found not a lot of pressure, and was able to add a little more antifreeze . Driving away, I thought that wasn't enough to make a difference. I thought of gunning the engine to help increase pressure in the engine, quickly got up to 70, and shortly, watching the scan gauge , that did it, and temperature went to 185. Note , over the weekend I hadn't driven on the highway, just in town, and assumed cabin heating was the signal all was clear, when it wasn't. Only a little more antifreeze would be added the next day after the highway trip.


* Engine drain plug- from prior post of tochatihu (I missed this earlier)

The radiator drain plug is as described in the tech manual, but the engine drain plug is not. To access that one, put the front end up on at least 4" of lift and crawl under. Between the engine and the firewall, look up for a 10 mm bolt and a metal drain tube on the engine. I'd call it about 6 " straight up from the vibration damper on the right drive shaft.

Another tip I missed from Patrick Wong that I just noticed today;
For a while, I forgot about the valve at the left-side top of the radiator that allows air to vent when coolant is added. After I remembered to open the valve (using a 6 mm Allen key), then work went smoother. However you must be careful not to allow coolant to spill out of that valve. End quote.

Edit, I want to say my next coolant change will use more short but higher speed driving, its my belief that the high speed rpm's and resultant higher coolant pressure will give the fastest purging of the air from the engine cooling system,(lacking other equipment), with the close watching of engine temperature . (Revving an unloaded engine is not a good thing, what I've heard). Am interested if anyone tries this.

 

So anyone just do a straight radiator drain and fill. I was thinking of just doing that once a year.

 

The pink Toyota SLLC coolant, when factory-fill, is rated for 100K miles service life; then refills are rated at 50K miles. I do not think it is necessary to change the coolant sooner than that unless you notice debris or rust in the coolant.

The capacity of the radiator is probably 1/3 of the total system or less (including engine, cabin heater, and coolant heat recovery canister) so if you only drain and fill the radiator you'll drain only a subset of the total. Even when opening all three drains, I find that only ~2/3 of the rated capacity is drained out.

I had previously posted my procedure (last year, I think) for running the coolant heat recovery pump "by hand" in order to fill the canister faster and avoid the issues that northwichita faced with his lengthy refill, depending upon cycling the engine hot & cold multiple times. Basically this involves finding the CHRS pump relay which is located in the relay box mounted to the center of the cowl, pulling it out, and shorting the switched terminals to power the pump. However this is not sanctioned in the repair manual which expects you to have access to the Toyota diagnostic laptop or handheld tester to power the pump. So beware, and don't run the pump more than a short time before letting it rest.

 

Does anyone know a "video" DIY for radiator engine and inverter coolants replacement?

 

Very nice research!