To cut to the chase...do the thermostats function like all the others I know of? Full open or full closed are the only two possibilities or is there now a partial open function? TIA!
The thermostat operates on a termanally sensitive spring. It softens when it warms up; allowing fluid pressure on the other side to pass as it gets up to the designated temperature. Any contaminants or rust can impair it's operations. (ie. get it stuck closed, open, or partially open) Hope this help
If you're talking about the one in the hose elbow down by the water pump, I think it functions like all the others I know of. A spring holds it closed, and a pellet of wax trapped in a cylinder expands with heat and pushes it open. It's a slowish effect, nothing sudden about it. The thermostat starts to lift a bit above 80 ℃, definitely opening by 85 ℃. It should be fully open (10 to 14 mm lift) by 95 ℃. House thermostats on the wall, now those frequently are just on / off (though even that has been changing in these modern days of variable-rate furnaces, A/Cs, and heat pumps),
Car has 152,000 miles. Yep, looking at the engine t-stat. I was headed to Denver when I got the dreaded coolant dummy light that turns off quickly on a long steep climb out of Phx on a very hot day. I usually push the engine to the pwr section during these climbs but after that I backed off and crawled up with the slower vehicles. Everything was fine until the final long steady climb on I-70 right before the descent into the Denver area and then it came on again and did its thing so I backed off and made sure to stay out of the pwr range. Did some research and changed the water pump in Denver. Drove all around the Denver area for a week without issue. Drove home via I-25 and I-40 route at 80 mph with no issues until the final climb into the Flagstaff area on I-40 which is not steep but long and constant. Same thing, light on/off so I again went to staying out of the pwr area. Did the same thing and crawled up the last but very steep climb on I-17 out of Camp Verde and never saw the light. So now that I am home and have all my tools available it is time to figure it out. I just purchased a reader and used it all day yesterday and the temps never got above 195 F. (On a side note the strange thing was that on the first trip it gave me the water pump rpm stats but nothing since. I've read that it normally doesn't read the rpm.) So now I'm thinking the thermostat may not be opening fully since it seems that it only happens in extreme engine use and what I can only assume is the upper temps of the t-stat range.
That's a weird part of your story. What reader did you buy? The car's ECM will answer the pump-RPM question any time the reader asks. The easy test for that is to take the stat out and suspend it in a pot of water on a stove with a suitable thermometer, and heat the water up. You are looking for noticeable opening between 80 and 84 ℃, fully open (10 to 14 mm lift) by 95 ℃, just as in the picture. If it doesn't do that, replace it. If it does do that, your problem is something else. (This is a better approach than just saying "I'll replace the stat and see if that fixes it", because then if it doesn't recur right away (say, the conditions are somehow different on your next climb) you can go around for a while with a false sense of having fixed it, and then later see that you still have some other problem.) Other problems could be restricted coolant flow, restricted airflow through the radiator (lots of bent-over fins or trapped debris). Check the operation of both radiator fans; they shouldn't be needed much when the car's in motion, but they should definitely both be running at HI speed well before that light comes on. If the coolant ever went unchanged a really long time, there could be corrosion products in the passageways reducing flow. If a stop-leak product was ever put in, passages could be gunked up with that. It would definitely be nice to get a continuous scan-tool display of temperature and pump RPM.
Yep; at a minimum I'd install a continuous ECT monitor, to keep you out of the danger zone and avoid blowing a head-gasket; while trying to figure this out.
It's common for third gen water pumps to fail around 150k miles. It's prudent to change the pump and thermostat, say every 100k. Ever cleaned the EGR system?
Not the cooler and valve. Just did the tube and as far as possible on the intake and EGR side. On my list and the timing of it will depend on what I see on the scanner.
Did you save the old water pump? Did you inspect the impeller on the pump and did it spin easily? The new pump that you installed. Was it Toyota OEM, or was it an aftermarket pump?
Verified those when I put the pump in. Coolant looked good coming out. I changed it and the inverter coolant when we bought the car used from the dealer even though they said they did it. I can't remember how many miles but my best guess in the moment is that it was due (100,000) over minimally overdue. The car has a lot of highway miles as we did a biannual trip from Phx to PNW every year for 4 years. And now multiple trips to Denver over the last two years.
Was the new water pump oem Toyota? Lots of aftermarket units are suspect. No head gasket sealer in your ownership? Radiators do get compromised with sealer. Use your Car Scanner to display both coolant temps so you know if both agree or one is high causing the alert. The 7C0 thermistor is monitoring the output of the exhaust heat system, which is only in full use during warmup. It also has a mechanical thermostat which allows exhaust to bypass the exhaust heat system's heat exchanger. I have heard of one case where that mechanism failed causing too much heat to 7C0. It's not clear to me that would actually overheat the engine since it's a small flow which is always picking up some heat from the exhaust no matter what. It does not take a mountain climb to raise the temperature as a test. Just find a half mile steep hill (the kind with the high grade warning sign), usually in a rural neighborhood, and drive it aggressively with max ac. It should not exceed 205f with a good cooling system. The most common problem is an aftermarket water pump replacing a failing oem pump.
I did spin it and it was not as easy as the new OEM one but I wouldn't say that it was jammed or really hard to spin. The first drive with the scanner showed the rpm as slightly higher than the request value. Now the only value I get is the WP duty @65%
Lots of good stuff there! It is OEM from Toyota. I about dropped my phone when they told me the price! No sealer since I've owned it. I will be testing it on some kind of hill, not many in Phx meet the requirements.
