No heat at idle - Heat gets warmer when above 1500 RPM

If the flow rate is sufficient. bubbles will be entrained and removed to "slower" portions of the system.

red line would set a limit on maximum flow rate.

 

Old cars (pre 80's) used mechanical water control valves. The last time I remember seeing one was on an early 80's Jeep Wagoneer. As the vehicle HVAC systems got more advanced the mechanical valves became less common.

 

Agree if you have enough volume - industrial chilled water systems for example.

The water pump in a vehicle isn't all that powerful, I have never seen the red line the engine method work.

 

VW and Audi used cable-operated heater core valves into the mid-1990s.

 

Funny, the last VW I rode in was a 1976 Rabbit - in about 1982.
Hadn't thought of that in years.

 

Water Pump. I had this same exact problem with Dodge Caravan work vehicle. Took to a local mom and pop shop twice and they could not diagnose. Finally took into a dealer and they discovered the impeller seal was leaking air ever so slightly. At idle, the water pump was not rotating fast enough to overcome the leak. But at hwy rpm's, there was enough pressure to overcome and circulate the coolant. The dealer confirmed by putting some dye in the coolant and using a UV light.

 

My very first car was a 1976 Rabbit, bought it around 82 or 83, lol.

 

@87TURD
Any updates??
Inquiring minds want to know.

 

I'd lean toward water pump as well, since that is the only thing that varies with rpm.

And if like you said, the top rad hose is hot but bottom is much cooler, that's another sign the pump is having trouble pushing enough coolant up and out the top rad hose at idle.

 

Well after all that, I learned a valuable lesson that unfortunately is the way all things are trending towards whether its vehicles, houses, or any manufactured goods. If you try to save a buck and do it yourself you will probably get fucked when things go wrong.

So 12/23 I bring my truck in. Explain to them everything that has happened as described, mind you its 8am, grab my coffee and start working. About 10 min later the technician comes out and says we think its your thermostat. To my surprise I said "interesting, that seems weird to me as I just replaced it." He said you did and I said yeah check it out. Show them the receipt and show them the old "water inlet housing" t-stat for normal people.

so by this point the master tech and shop foreman come over and said well can we check your install process and verify this, I said yes of course. so master tech and foreman verify that the part is new as they had already called around for the Factory OEM T-Stat and the only place that had one was the dealer ship I had previously went to 2 days prior and bought the part. They said well it was installed properly and we have never seen a new Water inlet housing be bad. I said me either. They said if that was bad from the factory you might as well go by a lotto ticket. They also said that its not like the old school thermostats that you can boil and check the functionality of it as they are imbedded inside the plastic housing...

So at this point with the verification of the new Water inlet housing, The master Tech takes over the truck and wants to start checking for other possible scenarios. Finally at 3pm I get my truck back and he states I think it just had a shit load of air in the system and was a pain in the ass to get it out, but it seams to be working now. So at this point im pumped, got my truck back walked out unscathed for 160 bucks and they had waisted almost all day on my truck.

I drive out to head home and with in 5 minutes I start watching my temp gauge jump up past middle again and sure enough start climbing past where I feel comfortable with it. I immediately pull over and let the truck idle to see if I'm getting heat. sure enough it starts blowing cold air so I turn around and back to the dealer ship. Well now they are completely confused along with my self. Well unfortunately for myself my service department does not give loaner vehicles anymore. ( I fact checked this and apparently Toyota dealerships across new England are starting this trend of only offering loaner vehicles to customers that have vehicles under warranty)
So now I am forced to rent a vehicle at 45.00/day. Master tech says he will jump on it first thing in the am and see if he can figure out what the hell is going on with the truck.

12/24 I get a call by noon saying there is still no remedy he tells me he has done the following
-radiator flush to check for a blockage
-heater core flush to check for the blockage
-checked all the hoses
-(2) head-gasket leak checks
-Pulled the water pump off and verified it is functioning properly

He said listen I have never seen this before and seen these types of symptoms happen at the same time no heat at idle and the wacky temp sensor readings. He said I know this sounds crazy and we have verified that the "Water inlet housing" (T-Stat) is only 5 days old but we want to order another on and see if that's what it could be.

I said at this point you've just spent another day on my truck with no conclusion I guess do what you think needs to be done. He said unfortunately we cant get one until Tuesday so Ill have to leave it it in the yard and you'll have to continue to keep your rental until Tuesday. at this point I'm livid but I have no option.

Well Tuesday roles around and sure as shit I get a call saying my truck is done. and looks like I bought a bad water inlet housing that was a factory Toyota part. Hop in my truck and sure enough heat works at idle and no overheating symptoms.

I check out and get a bill for 765.00 dollars. so needless to say I decide to call Toyota Corporate as the dealer ship already ate half of the labor spent and incurred the following expense because they sold a faulty part
- 12/18 Antifreeze, Toyota Water inlet assembly - $151.00
- 12/23 - half day of labor at the dealership - $163.00
- 12/24 - Diagnostics and full coolant system tear down worked on the truck all day
- 12/28 - Incured costs from 12/24 and another water inlet assembly install plus part - $765.00
- 6 days of vehicle rental @ $45.00/day - $270.00

For a total of $1,349.00 dollars all because I won the lottery and purchased a water inlet assembly form factory Toyota that was bad from the get go.

I decided to call Toyota HQ and explain my case and explain to them how is it fare that I incurred all this cost because they sold a faulty part. after 1hr on the phone I got now where. I was told about 10x that because I installed the part my myself that they were not liable for any of the decisions were made by the dealership to continue to work on the vehicle. They said if it was my dealership that had installed the part and it was bad then it would have been their problem and not mine. As a matter of fact the customer representative I spoke with from Toyota was a complete snooty little asshole and am blown away they have people like this to represent them. And personally because of this incident I will never buy another Toyota again. Unfortunately no I am not a certified Toyota technician, however I've rebuilt countless small block V8's, I've worked on snowmobiles and my race bikes, I've worked on all my classic boats, I'm not a complete dummy when it comes to things like this. And the fact that I took some initiative to install my own water inlet housing done properly and torqued to spec and happened to get a dud from the factory that its myself and the dealerships problem... This attitude will make me never purchase another Toyota as long as I live.

Moral of this story, when it comes to a company like Toyota, don't do anything yourself that is simple. Because if you do and you get to the end of the road when diagnostics require their proprietary equipment. regardless if the part is faulty or not they are just going to want to start with the simple shit first. And in my case when it is a faulty part you'll get left holding the bag for countless hours of diagnostics around chasing a ghost.

 

Toyota Parts Warranty "All genuine OEM Toyota parts have a 12-month unlimited mileage warranty."

With all the documentation that the part you bought over the counter is bad, you should be able to have that part warrantied over the counter where you bought it and have a brand new one in your hands. Then sell that.

 

Can't like that post but thanks for the closure. Sorry about all of this.

If there is a small good part to your ordeal it is that you might have helped another person in the future.

 

My 2005 V6 just started having this heat issue last year before my deployment started.

I tried blowing out my heater core which seemed clear (didn't see any debris), replaced my thermostat, replaced my air blending actuator, then threw my hands up and took it to the dealership.

The dealership told me it was more than likely my water pump going bad, so they replaced it and charged me a pretty penny for it.

Fast forward a year, I came home from my deployment to my truck still not blowing warm air at idle. I returned the truck to the same dealership and just got told its the thermostat, thermostat gasket, and fan clutch. This will supposedly be $700 to fix according to them.

 

Wonder how it would've played out if you played dumb and they didn't know you changed any parts...

 

Thats all well and dandy but doesn't cover the wasted labor that was caused by the faulty part in the first place and toyota taking a "not my problem approach, 1200 shelled out for researching other possibilities after they found out I had just installed a new one