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I am thinking that the thermostat in the engine needs to be replaced. So, my wife was driving yesterday and she said the temperature gauge would rise very high when sitting idle but once underway it would come back down and that the heater wasn't very warm. When I checked it out I found the coolant reservoir was empty but the radiator seemed full. I didn't have any coolant on hand so I filled the reservoir with water and started the engine and let it warm up. I let the engine idle until the gauge was right in the middle then I turned on the heater and I didn't feel any heat. I then took the car down the street and in about a mile or so I started to feel some heat. The gauge stayed in the middle but then slowly started to rise and then it would go back down a bit like normal. I then noticed that the heat would fluctuate drastically, I had the heater on high and it would go from really good hot heat to no heat at all. As I drove the vehicle the temperature gauge started to really rise so I drove the vehicle back home. Also, the fans were working as normal the whole time I was operating the vehicle. I am wondering if this sounds like a faulty thermostat, like the thermostat is sticking causing the temp to go up and heater to fluctuate?
What do you guys think?
When was the last time a timing belt was replaced? The timing belt kit in those cars also includes a water pump with it, the reason for my question is just to make sure that the pump itself is not as vintage as the car itself and it doesn't cause issues.
Issues with thermostat are usually linear, aka if it is stuck open, the the car will never get to temp, if it is stuck closed, the engine will eventually seize. With that, it will never hurt to replace it for preventative service when the next maintenance is due. Make sure to only use OEM thermostat though, this is not the part to cheap out on, and it doesn't make much sense as aftermarket ones cost about the same.
In your case, however, it sounds more like an air pocket stuck in the system somewhere, which may very well be causing the temperature fluctuations, especially considering that your coolant reservoir was empty. To make sure, get one of the kits linked below, then fill the funnel about halfway with coolant and start up the engine, letting it sit for some time, then go for a ride to see if that fixed the issue.
Other thing to mention is that there is a reason for a reservoir to get empty, the coolant doesn't evaporate out of the system on its own, so either you have a leak developing somewhere, or it may be a result of a bad radiator cap that can no longer maintain the pressure in the system, dumping the excess fluid. With that, just make sure there is no air in the system first, then verify there are no leaks around the engine, and only then start digging towards a new cap and thermostat.
There is a rather complicated coolant bleeding procedure for these cars, but even when I follow it, I end up topping it off after the first 3 or 4 trips, then it will be good for years. Be sure to run the heater full blast on your trips for a bit.
Steps from service manual to bleed coolant, key is to fill it at radiator filler neck on driver's side, be careful, that is the hot part...
1) Loosen upper drain plug 2) Put a clear vinyl tube on vent plug located on upper drain plug 3) Fill radiator at filler neck (not overflow tank) until vent tube full 4) Install radiator cap, tight 5) Fill reservoir overflow tank 6) Warm up engine and while it is running squeeze the inlet and outlet radiator hoses by hand several times 7) Stop engine and let it cool 8) Remove radiator cap and check for fluid level in radiator 9) If coolant inside radiator (not overflow tank) is not to full mark, repeat steps 1-8 until it is 10) Top off reservoir tank if needed.
Then for next 3 to 4 trips of 10min+ (turn on heater for a bit full hot), check tank when cooled off. It takes about 3 trips to stabilize.
Thanks for the replies. I inherited the RX from my Dad and haven't had it very long and do not know the details of any maintenance history of the vehicle. I have ordered a OEM Lexus/Toyota thermostat and will do a complete cooling flush when I replace the thermostat. I will keep an eye out for any leaks, haven't noticed any and the oil is clean. The radiator cap seems to be holding pressure because after driving it when checking it out, I checked it by slowly opening it and it had a lot of pressure. I think the best thing to do is to go ahead and flush the system, replace the thermostat, check all hoses, inlets and outlets, check reservoir tank for any cracks/splits, purge system of air and hopefully that will fix any issues. Thanks for the tips.
The radiator cap seems to be holding pressure because after driving it when checking it out, I checked it by slowly opening it and it had a lot of pressure.
All is well, except for a fact that fluid is not compressible, no matter what kind of pressure you have in the system, you will not get a fountain like in pneumatic system out of hydraulic system unless if the pump is running, there is no stored energy in there.
The whole reason to keep the coolant under pressure is to increase the fluid's boiling point, so that it can handle more temperature without boiling over. Fluid is not compressible, but the vapor is, should there be a be a sudden failure in the system that lets the fluid boil in a very short amount of time, it will cause a catastrophic blowout instead of a simple leak. When you loosen the cap, you drop the pressure in the system, causing the fluid to start boiling instantly, and that is what in turn creates the fountain that you get out of the cap, and that is why you should never do that, not only it doesn't check the system, there is a good risk of getting burned in the process.
If you don't want to replace the cap just yet, some car parts stores have equipment to test the system in general, and the cap in particular that they can rent you for free, and that is what I would do for a peace of mind.
Thanks for the tip. I didn't completely remove the cap, I only turned it slightly, once I felt the liquid start to boil and felt some pressure I tightened it back down, I was mainly wanting to see if it was leaking anywhere, which, it wasn't.
Looking at the t-stat tell us yo have a 2gr......So no t/b or a easy water pump change....Little more work to do a w/p swap on a 2gr thou......
What is a 2gr or t/b? I know the timing belt and water pump are in the same housing, is that what you are talking about?
I have a 2000 RX300 also and had to replace the engine last year and had the timing belt, hydraulic tensioner, and water pump replaced as well as the thermostat before the engine was installed.
Okay, I see now that 2gr is the engine designation. I was going through the owner's manual and thought that I had seen an invoice where Dad had some work done on the vehicle and sure enough, I found it. In August of 2019 he had the water pump, thermostat, and serpentine belt replaced. I pulled the numbers for the thermostat and it was not OEM so, I am still going to replace it. I have noticed also that the area around the radiator cap is really dirty like maybe it has been leaking or spraying coolant, the air filter box and surrounding area are not wet but they are dirty.
This is what I am referring too, you can see how it is dirty around the area near the radiator cap. I have also included pictures of the inside of the cap but I can't tell if it is good or bad, and yes the battery has some corrosion on the terminals that I will also clean.
Well I got started on replacing the thermostat, drained the radiator and started to remove the serpentine belt and quickly realized that I needed a special tool because I couldn't get a breaker bar and socket on the tensioner pulley bolt so I got a loaner serpentine belt removal tool from Advanced Autoparts. I was able to remove the belt with the special tool and then focused on removing the idler pulley but ran out of daylight.
I wanted to make sure that the idler pulley bolt does not have left hand threads before I really crank on it so, can anyone confirm this?
12-10-22, 06:54 AM
Engine Temperature and Heater Fluctuations
