What's your method? I want to flush out all of the old green Prestone and replace it with Zerex for Asian cars. Can I flush with tap water and then rinse with distilled or should I only use distilled?
What's your method? I want to flush out all of the old green Prestone and replace it with Zerex for Asian cars. Can I flush with tap water and then rinse with distilled or should I only use distilled?
I've used distilled for the entire flush process. I've gone with the Eric Collins method except I don't remember whether I lifted the front so much as had it on a slight incline with the nose up a bit as my driveway conveniently slopes down from the garage.
When you drain each time, get a complete one by removing the additional drain plug underneath the block (my notes say it is mentioned somewhere on this site - it's a 10mm verically-oriented bolt that's near the oil filter
924114761-PREVIA-ENGINE-BLOCK-DRAIN-PLUG.jpg).
Saved from - where else- the Yahoo! Previa Group -
"Previa Coolant Fill Suggestion
...with the front end lifted, I fill the system with distilled water, run the heater on max, hold the revs around 2500 rpm to warm up the engine and get the t-stat to open, then I can usually put another gallon or so of water into the system. Then I drain the radiator and the block, and repeat this about 6-8 times, or until the drain-off looks clear. After that, I know the system is 100% distilled water, and can then add 50% coolant (based on total capacity of the system) to arrive at a perfect 50/50 mix. I let the coolant circulate through the system while the van's still lifted too. Then just top off with more water to the "max" line of the tank once the engine has fully cooled (usually the next morning). Might have to top it off a few more times until everything settles.
Never had a problem with air in the system or overheating issues by following this method. (In fact, I think the previa cooling system is the least troublesome I've dealt with. Original water pump and t-stat lasted 15 years and 290k miles (just lucky??) and I've run for months before with no fan installed. Wouldn't even overheat just sitting in the driveway at idle for hours without the fan...the temp stayed steady at half-mast the whole time. That said, it's important to ALWAYS carefully monitor the engine temp while flushing the system--it's not wise to let it idle in the driveway unattended.
Eric C."
FWIW, when getting the air out with the front lifted and cap off reservoir, rev to 2500-3000 rpms for a while & monitoring/filling the system.
Oh, and get one of those deep funnels with a radiator-cap adapter that include a removable plug-on-a-stick to close them off from the top when you go to remove it with fluid still in it. Total game-changer vs watching fluid bubble-up and overflow when things get hot. You can just watch it "burping" instead as the air bubbles come out.
"If you find yourself holding a sledgehammer or a crowbar, it's time for a break."
Dan and Yahoo for the win. Can you actually reach the block drain without lifting the van? I often change the oil filter without lifting it, but it isn't always easy. I've never looked for the block drain but I'm trying to change my ways and do regular and proper coolant changes. I need my klunkers to last a long time.
I'll get one of those radiator funnels tonight. I can see where that would be very handy and I need to do this with my 4runner too.
My memory's a bit fuzzy except for a recollection of gallons and gallons of dirty coolant & flush that I had to get rid of (I had to flush multiple times until things looked clean). I actually must have lifted the van - it's really tough to get underneath there otherwise. On further reflection, I also don't recall that I did tilt the front upwards. Looked thru my notes & see I forgot to mention something important - when you fill it with coolant, there's a "bleed screw" accessible on the side of the engine you get to by removing the passenger side engine cover. Opening it and closing it again after some fluid starts coming out during the fill eliminates a bubble of air that can form at that high point in the cooling system.
Pg CO-5 on my '92 Repair Manual specs the torque on the Engine Drain Plug at 13 N-m (130 kgf-cm, 9 ft-lb). (Yeah, I have a full set of torque wrenches down to the #@%!! - you-just-stripped-the-aluminum-threads,-didn't-you range...)
Again, from the Y! archives (don't know who posted it)-
751398503-Sensors-and-Bleed-Screw-Locations.jpg
FYI here's "Eric the Car Guy" (man, haven't looked at his stuff in forever) using one of those funnels at the 2:15 mark
https://www.youtube.com/watch?v=zUpXgAJ1gjU
Last edited by man_btc; 10-19-2024 at 04:59 PM.
"If you find yourself holding a sledgehammer or a crowbar, it's time for a break."
Oh great, an engine bleed screw that I have to take the passenger seat out to get at. I love how easy these things are to work on!
I think using that bleed screw means you don't gain an advantage by tipping the front up, but I don't know enough that I'd argue the point with anyone.
"If you find yourself holding a sledgehammer or a crowbar, it's time for a break."
I too always avoided removing that panel. The Previa tends to get air bubbles after draining/refilling coolant, but I never used the bleed screw. I didn't know the trick about lifting the front, I just filled it until it quit accepting more, then took it on a rigorous test drive. While driving I watched the temp gauge and typically it would go up a little higher than normal then settle down to the normal spot. After that I would come home and top it off. Never had an issue doing it that way. Tim
Thanks Tim, for encouraging my laziness. I must say I haven't had any issues just filling it through the upper radiator hose and tank, then topping it off as needed. I've drained it 3 times since July and never took that bleeder out.
Got some Zerex today, and am ready to go red-ish.
Filling through the upper radiator hose is how I always do it. In my professional mechanic days, that's how I filled almost every engine I worked on. Fill through the hose, reattach it, fill reservoir, test drive, then top it off after it cools.
Edit: The upper radiator hose is for engines prone to airlock, typically by having the thermostat super low.
On my van today, I would probably not do that, because my radiator is still somehow original and I'm afraid the plastic would break. I need to consider a new one, maybe all aluminum?
Yup, I fill it the same way after draining it. Good luck finding an aluminum radiator-did they ever even exist for a Previa? They had plastic tanks even in 97, I believe. I know my 97 4runner has the original radiator with plastic tanks
Well on the 2nd flush (and I will need at least one more) i seem to have developed because I don't have heat. I guess this is where the seat comes out.So much for canoeing today.
I finally got it heating, but crap. I forgot all about the engine drain plug, duhhh. That's probably why I'll have to do a 4th flush, duhhhh. Duhhh.
Turns out I don't have the bleeder screw, hahahaha.It looks like someone might grinded it off, hahaha.
OK this time I drained the block too, but I hope I haven't opened a new can of worms with this green to red project. This time it took even longer for the heat to come on. It was already fully warmed up and topped off, and I drove nearly 10 miles before the heat blew hot. I only have time to do one more cycle before work today, I've kinda lost interest in doing this to my 4runner this year.
Heya, I'm doing a green-to-red flush today as well. How many flushes did it take any of y'all to get clear water coming out? I'm on my third and it's still green AF. I'm draining at both the radiator and the engine block, refilling with distilled each time, and I had the nose raised for the first two flushes. Heater on. I'm getting a little under two gallons pouring out each time. That's only 2/3 of the capacity, right?
12.3 quarts capacity, but not sure you can really empty the whole thing out, it's really about getting it clean, adding the right amount of coolant, then topping up with water so you know it's 50/50. I suppose after one of the drains you could disconnect and check out the heater valve to see it it opens all the way?Originally Posted by Bekaykay
The common wisdom is 6-8 flushes as described earlier. That was my experience.
The tilted-up front method is more about getting air out when you're all done rather than during draining.
"If you find yourself holding a sledgehammer or a crowbar, it's time for a break."
Yep, mine took 8 flushes after all. By the fourth flush, I started removing the upper radiator hose and a TON more fluid would come out. I had the passenger seat out, so the upper hose was easier to reach then the lower one. So yeah if you're going to completely replace the fluid, buy a whole shopping cart full of gallons of distilled water. Not too bad compared to paying someone to do it.
I just flushed and replaced my coolant for the first time. I did not need to change coolant types, but I can comment on the difficulty of draining and refilling. I unbolted the thermostat housing and that made draining in a realistic amount of time possible. Also removing the thermostat itself made it easy to run flushes quickly. So my process was:
- open radiator drain,
- open engine block drain,
- open engine block vent,
- wait a minute for those drain down most of the way,
- unbolt thermostat housing,
- drain full system down (maybe 3-4 minutes),
- remove thermostat and bolt thermostat housing back on,
- fill with distilled water and run engine (1-2 minutes) to flush water around,
- re-drain.
For my van, I was running pretty clear water after just one flush, but if needed, that procedure went pretty fast with the thermostat removed because you do not need to wait for the engine to warm up.
Refilling fully was a pain for sure and took a lot of engine cycles and burping the engine block vent under the passenger seat for me. I know some people say fillign the top radiator hose helps a lot and I think that is likely worth the trouble. It took a lot of faffing about to get mine fully filled.
Interesting. So you're dealing with a total volume ~100 quarts (or liters), a total weight ~200 pounds (or 100 kg). How scrupulous do you have to be with the waste? - at what point does it go into the untreated run-off?
Last edited by John Kaufmann; 03-17-2025 at 11:50 AM.
Isn't it toxic in any appreciable concentration? And by "appreciable," I mean something I certainly don't know enough to judge (I have repeatedly failed to understand most of chemistry), so pretty much anything flushed out.
Took my quiddley-two one-gallon jugs to my town's Toxic Waste Collection Day when it came around (and I remembered to do so).
"If you find yourself holding a sledgehammer or a crowbar, it's time for a break."
I got about 2 gallons out each flush, which is why it took so many rounds. So that was 16 gallons. I poured it all back into the distilled water containers and brought it to the household haz waste facility. The guys that work there LOVE the previa and see me on a fairly regular basis for one car project or another.
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