what did I learn about my cooling system today, if anything?

OK, I'm moving on to my 03 that's losing coolant. No smoke, no residue in the exhaust pipe. Nothing except the AC dripping under the car. Yet, if I fill it up, it'll lose enough coolant to trigger the red temp light after about 100 miles, maybe 150.

So, I borrow a pressure tester from the parts house. Don't know what the max pressure it'll hold, but don't figure that's important and only pump it up to about 5lbs. I just need to see if it holds. And, it doesn't. Slowly (I assume) leaks down. I leave the tester in place and start the engine, with the AC on - this is the part I'm not sure about - and it never builds pressure on the gauge. So I pump it up to 5, and it stays there. But, if I release the pressure, back to zero and never builds.

Shouldn't it build pressure? Would that process measure the pressure while running (the instructions only talk about using the tester with the engine off and cold)? I let it idle like that quite awhile, ICE always running, and never see any dripping from the hoses, radiator, or underneath. I can't quite see the bottom of the water pump from above, and I didn't take the plastic shield off underneath to see from there, but I'd think it would eventually come out somewhere.

I squeeze the hoses and they have pressure, although I can push in some. Is there any other potential leak sources I'm missing - hoses, water pump, radiator? Forgot to check the passenger floorboard, but haven't noticed it being wet. I also don't see anything leaking out of the overflow bottle although, again, I can't see the bottom and assume it would drip underneath.

The tester instructions say that if it loses pressure slowly, it's a minor leak, but I'm not sure what "slowly" is. I'd say from 5lbs to 0 in less than a minute. At first thought it was leaking real fast, but the tester cap wasn't on tight enough. Is 100-150 miles a long time for it take to leak out? I had to put in most of a gallon of distilled water to fill it up? How much coolant does it hold?

 

Well, I'm not sure what to do since I don't see any leak. Thinking about replacing the water pump just for the heck of it - thinking that's why I'm not seeing any pressure build and this car has 212k miles. I know pumps in general will fail internally sometimes, the blades disintegrate or it quits spinning on the shaft. Still, that doesn't explain the loss of coolant.

Is there any sign of a blown head gasket other than coolant out the exhaust pipe or a compression test? If that's where I'm losing coolant, doesn't it have to show up as exhaust smoke or dripping pipe? The ICE/engine actually runs wonderfully.

Oh wait, I never checked whether the oil is milky. I'll go do that now. Can coolant get in the transmission fluid?

 

Oil looks fine. Went ahead and removed the plastic shield from underneath so I could see the water pump. Nothing coming out the weep hole or anywhere else around it. I do see white stains on the block behind the crank pulley and behind/up from it. Let it run for 10-15 minutes and no drips anywhere except very cold water coming out the AC tube. Surprisingly, I see what looks like a second AC type drain tube about parallel with the one dripping and further forward, like it's coming out the front of the firewall/whatever and the other tube comes out the bottom of the car, behind the crossmemberish, lower suspension arm? But it's not dripping. (Sorry, inside the house now and didn't study it intently enough to better describe). I could swear, years ago, when I had that tube get clogged up and cause overflow inside the cab of my first Prius that it was that forward tube I cleaned out. Soon as I saw it, it looked very familiar.

But, with the water so cold coming out that rear tube, it's gotta be AC related, and the volume is what I'd expect.

 

Also, no sign that the overflow bottle is leaking. I filled it up to the brim and 30 minutes later, it's still full. And, I don't guess such a leak would cause the engine to overheat if the radiator starts out full, right? Does water flow from the overflow into the radiator, or reverse, or both? It's always empty too when it overheats.

 

Thinking about replacing the water pump. It looks the same as the Camry I did a few months ago. Easy enough although even less room in the Prius. My worry is that this is now my only car, and I don't want to tear it down then need something I forgot, or worse, some little tool, since all my tools got stolen and I only have a basic socket set and wrenches.

Dang, I need to get this one fixed so I have a good car to drive and can then focus on getting my shuttle bus road ready so I can start making money again.

 

Drove it around tonight - I take Brody for country drives on 4th of July to escape the fireworks - and with the lower plastic shield still off, looked all underneath when I got back. No signs of leaking coolant anywhere. This is pretty crazy.

I'm wondering now if there is a blown head gasket, despite no obvious signs. I assume that, depending on where the gasket blows, it doesn't have to leak into the oil, so that the oil looks fine isn't conclusive for the head gasket being good. How about the fact that it runs so smoothly - the best riding/running (except for the overheat) of all my Prii? Would coolant running through the cylinders not affect the way it runs?

If so, it might explain why it was at the auction. It wasn't wrecked, and came with a clean title (no insurance total), but at the same time, it didn't run right when I first got it. However, by the time I got around to working on it two years later, the HV battery was dead, and replacing that and some injectors, IIRC, and the AC compressor made it run great. But, it's typically many weeks after a car comes to the auction before it's actually put on the block, so the battery could have crashed in that interim, and the original problem might have been a head gasket??? The car was so nice - as I've said in earlier posts, I've owned a lot of cars and never saw a 200,000 mile car so clean - that you wouldn't think an owner who cared about it so much would toss it aside just because of a bad HV battery.

So, is the only way to know running a compression check? Can the dealer tech tell using TechStream?

PS, come to think of it, I think I replaced the inverter pump as well - but that would have burnt up the inverter if driven, not cause an ICE coolant leak, right?

 

Hmm, I don't know. Maybe someone else could answer. I don't recall seeing anything that looks like coolant lines going to the throttle body. Thanks for suggesting that.

 

Interesting. So, the coolant could be leaking into the TB? It's not leaking around the connection, wherever that is, or I'd see the drip. And I'm losing coolant pretty fast. Wouldn't that have an obvious effect on performance? Wouldn't I see coolant at the exhaust, or white smoke?

 

I'll check it out tomorrow. Not sure how to diagnose that. No CEL. Seems like that sensor by the cat converter might notice something wrong with the mixture coming out. I'll search here and google.

 

Occurs to me that this might be the reason for the seemingly random 3190 I got the other day. Coolant in the throttle body, lower performance, not enough torque, 3190.

 

Now, my faulty memory is coming back. Just remembered that this car wasn't putting out heat last winter. Our winters are so mild, it didn't bother me. Then, the first time it overheated, I added distilled water to get home, and the heater started working. So I figured it had just been low on coolant. I wasn't driving this one much since then, and now, of course, it's hot as heck, so I've not used the heater.

Trying to figure out those lines going into the throttle body, and thinking they may be heater hoses??? So if they're leaking into the TB, and the coolant is not making it to the heater core, that solves that issue too.

Does sound like the overheating, coolant loss, no heat, and 3190 are all related. I have TBs on both my parts cars, but I recall looking down one and it was ugly.

Dang, hate to tear into this because I don't have another car right now. Maybe I just keep limping this around by refilling with distilled water and minimizing my trips while I switch over to my shuttle bus and get it running so I'll have a way to chase down parts/tools when I tear into this. Gotta think through this, and I'm not good at that. Not any obvious threads on this here that I found and less on Google.

 

Ooh, good idea. I read some guys on ToyotaNation talking about doing that for performance gains. I haven't looked at this on the car yet, but I assume I'd have to block off the other end of each hose.

 

Y'all might be on to it. Bypassed the throttle body, filled the overflow and radiator as much as they'd hold, and drove to see my brother, about 50 miles away. Let it cool down and checked levels. Between the two I put maybe half a pint, no more than a pint.

Mind you, this is all distilled water now, and it was 47 miles on the highway, if that matters at all.

With them full again, I drove home. I put a little bit more in the overflow this time, and about the same half a coffee cup in the radiator.

Not sure what this means yet. It seems to be a major improvement. Maybe nothing more than routine air escaping after all those fill-ups. I do get bubbles that I have to let blow out before I can add more water to the radiator, over and over, until they eventually stop. Maybe there's more that don't come up until I drive. Also, my early estimates of the miles I drove until the red light came on were never measured, and I don't remember things well these days.

So, I'm going to just keep driving it around town, stop-and-go traffic - my normal errands, and see if it stops losing water over the next few days. probably research throttle body repair. Never heard of coolant leaking into a TB. Is it common?

I'll update. Thx for the suggestion.

 

Thanks, TMR, you're leading me in good directions. My brother also suggested that the water is just steaming off unnoticed. It's possible, especially around the radiator, as you point out, because I wouldn't see it behind the shroud.

I think the first step is to see if the TB bypass stops the coolant loss. Just because it's easy to do - just keep driving the car. Like I said, if my memory serves me well, and it often doesn't, the small amount of coolant loss I saw yesterday was a huge improvement and possibly attributable to just air inside. I'm also thinking coolant in the TB explains the random 3190 I got the other day - coolant/water in the intake affecting combustion.

So, I just finished driving about 50 miles. I had topped it off again, and again, I could add a small amount of water, maybe a couple of inches deep in a coffee cup, between the bottle and the radiator. Basically, almost none, but still some.

To speed up the process, I rented the pressure tester again from the parts house. BIG difference. Before, I pumped three times and it was only 5 lbs. Now, the first pump is more than that, and three had it at 13lbs. I don't think it was user error last time - I didn't get the adapter tight my first try, but I got consistent results after that. I think this test is accurate, and I really was leaking so bad before that it couldn't pump up over 5lbs.

It also leaked down real fast before, all 5lbs in less than a minute; you could watch the needle move. Now, it still seems to leak, but very slowly - about 1 lb. per minute, so slowly that it doesn't even appear to be moving.

One theory is that the bypass eliminated the original leak, but I'm leaking from the connector I rigged to tie those together. It was labled for use on vacuum lines, not coolant; just a cheap plastic tube, with small, cheap screw clamps.

It could be that I'm simply overfilling the radiator and bottle up to their rims, and they keep purging a little water, somewhere, when I drive to get to a workable level.

Maybe I just need a new radiator cap.

Maybe I'm now pumping too much air into the system with the tester, and it's purging air down to a workable pressure. I never let it keep dropping to see how low it would go. Soon as I confirmed it was dropping, I started over to confirm. Maybe it would have stopped at the right level? Dang, I turned the tester in.

Meanwhile, the car runs fine. No sense of urgency. Odds are that the worst case scenario is a TB cleaning/gasket. And that's only if I care to do it. Those lines warm the fuel in icing situations, which isn't really anything I worry about much here in Houston.

I'll monitor it some more, maybe buy a cap just because. Check those screw clamps again.