I can't help but think it's something relating to the thermostat still, given the intermittent nature. New parts can and do fail, so it may have tested functional (if they really did test it rather than assume it works straight from their parts shelf) but have some issue. Also, I don't know how likely this is, but could they have confused a thermostat with a different temperature rating, anyone know if this would cause the issues described?
Done at Toyota/Lexus Dealership, they'd use a standard OEM T-state almost for sure! Never seen new OEM bad. But if temp to low, it would just produce lower heat, not likely noticeably so. Heat would work all the time, just a little weak.
Thanks
@2001LC will check as you suggest, in fact coolant was a bit low when I first brought it in.
Engine temps seem normal to me I'll take pictures at those time intervals.
@CloudCity the vehicle has now had 3 t-stats during my brief period of ownership, the odds of all three being duds are astronomical, don't you think?
This is a clue "in fact coolant was a bit low when I first brought it in." How do you known this?
You can test the t-stats without replacing them. I would really triple check your coolant system as
@2001LC suggested.
I'm going to suggest a simple method to verify temp, which gives good indication of thermostat. But first we'll do the basic level checked.
@Dunnik is not a mechanic I gather, so will go step by step.
@2001LC Paul have you come across any literature about the angular orientation of the t-stat? i dont disbelieve you, am just curious as i feel this crucial fact isnt mentioned enough.
i still agree with others that there is air and/or not enough coolant in the system. very easy to verify and top off. of course "just replace the heater core" would be a great fix, but we all know how awful of a job it is to remove and replace. and it still goes back to how can both of them be clogged. there could be a clog but it would have to be forward/upstream of the T's and i would think that would present other cooling system issues.
tip that nose of the truck up with a cold engine, pop the cap, rev it like hell and top her off!!
theres always the burp bucket......it works
Well, seems I did read somewhere in Toyota stuff the purpose of jiggle valve is bleeding off air. Don't recall where, but google it and you'll see many say it is.. The FSM is very clear, on that jiggle valve needs to be orient at top. It's not likely a shop, 3 times in a row, messed up installation of a thermostat or it's jiggle valve. But that assumes more than one mechanic involved over three visits.
But not topping properly, is something I see a lot of times. Even from very good shops. First thing I ask people to check, to see if coolant system topped and working properly. Does the cabin heat blow very hot, when engine at full operating temp. If not, it is almost always low coolant level, especially if recently serviced with anything to do with coolant. So we need level verified first thing, it is the number reason cabin heat does not work both front and rear.
He also said heater core flushed. Well was that done at firewall and by isolation of just the cores one at a time? Likely yes! if their hunting and issue with cores. This means heater cores are fine, or they didn't do their job properly. Does that ever happen.....DUH.
I said withing 5 degrees of top. I see FSM gives more wiggle for giggle 30 degrees. But could this have been set wrong three times, I hope not!. Easy to check for someone with some minimal wrenching skills.
Clues something was going on with PO.
"new clutch (blower) fan " When I questioned what is this? : "the fan that blows the, in this case, heated fluid in the core into the cabin?"
I'll bet this was fluid clutch for fan (AKA fan clutch for radiator). This and coolant was low, indicate the PO had coolant issue.
Posting up history from both Toyota and Lexus may yield more clues. In USA we can get this info easy. In CN I was told we must get from Dealerships directly.
Here's another clue we've been given, and
@white_lx picked up on also:
"assume tested with fan on full, was told temps at the intake and outlet were within 5 degrees C, which, I'm told, is within factory specs"
That is 41 F.... WOW. Now I've not looked of the test for this nor how to do it. But my guess they just shot IR gun at in and out of cores at fire wall. I would expect with heater set on high and fan on high we take heat (energy) from the core and out would be lower. But 41 f is a lot. And if no heat in cabin, than energy is not being taken from core is it. HUM!
So a number of things are pointing to flow or temp of coolant. With three new thermostats why would temp be low... HUM!
It's either a flow issue, an engine coolant temp issue or electronics of HAVC (why asked about windshield, BTW: OEM glass doesn't insure it was from factory install or installed correct)
I'm being a little lazy here. Not to have looked some stuff up. But lets get through basics first.
I'll need too look up rear heater parts, but to not have front and rear working could be electrical, but likely flow or temp.
Next I'll be suggesting we check temp manually. This will be very easy and just cost $20 for and IR temp gun.
Post up a picture of engine bay. I'd like to see mat attached under hood (hood insulator), top area of radiator, front of engine and front of radiator. Basically anywhere you see pink crusty dried coolant.
