How's it going everyone so I'm dealing with this weird problem with my 98 es300. I'm going to explain what happen in order.

First off I replaced both my belts in the car and installed an aftermarket Injen Intake on my vehicle. Two days later on my way home I noticed the gauge in my car climb up damn near the H but didn't go into red, So I pulled over let the car cool down and seen that coolant has boiled and spilled out of my reservoir. I took my car home taking the side streets and it was still slightly climbing little by little then it was cooling down as I was coasting and letting air get to the engine. When I got home I checked my radiator fluids and it needed about 40 oz of fluid (Roughly 2 water bottles). So I topped off the radiator and my reservoir was fine since it had boiled some coolant was in there past the full mark. The day after it happen again on the way home from work but not to work since its early in the morning and the weather is fairly cold in the AM. So I parked my car when I got home and decided to start replacing my parts from cheapest to most expensive. I replaced the radiator cap, thermostat original owners had a opened thermostat that I wasn't aware of and I had already owned my vehicle for about 11months before all this started happening. So I replaced the cut thermostat with a regular one. Once I did that the car warmed up quicker but now also overheated quicker and I still couldn't figure it out. So I took apart my radiator and did a flush and noticed restriction so I went ahead and replaced it with a brand new one. Then i test the car out and it was still overheating. So this is when I decided to take it to my mechanic whose done all the work to my car. It was diagnosed with a bad head gasket. I went ahead and replaced the hg and once that was done my car was no longer overheating I think but now this strange thing was happening to my car with the temperature gauge. It warms up fine but once it gets to the halfway point it starts bouncing slightly until it gets to 3/4 then my fans turn on and cool the car down. When it gets to 3/4 It scares me thinking abouts about to go past that and into the red so I pull over and see no boiling or overspill out of my reservoir. So I told my mechanic about it and he suggested we throw in the old opened thermostat to see if it keeps the car cool. We did the swap and the car still does the same exact thing with the gauge it goes up to 3/4 before it starts cooling down. So now I was thinking it has to be a bad sensor. I went ahead and replaced the one near the radiator and the one above the thermostat housing. Well I'm still having the issue with the gauge and its worrying me. I have a digital thermometer and I hit both the top and bottom hose for the radiators and the temp is roughly 180-195F then I check the thermostat housing and its roughly 185-190F. To me that's normal operating tempt but the gauge is going high up to 3/4 and telling me something different? What could possibly be the issue here? I did my timing belt and water pump about 4 months ago so I know it can't be a water pump. Someone please help me!

 

attached is the FSM - COOLING SYSTEM for a '97.

Go with OEM thermostat - they are much beefier than aftermarket. Don't forget a new rubber O-ring for it too.

Injen Intake - is that just the snorkel in front of the throttle body? Or is it dealing with the plenum, etc..?

 

I currently have it with open thermostat (No thermostat) and I'm still dealing with my gauge showing me it's overheating but when I check the temp on the engine the temps are coming back fine. Yeah the intake is just a air filter opened enclosure pretty much. Could I have a faulty cluster needle or what can cause my needle to keep doing this? I can take a video and upload it if I have to.

 

does the heater blow hot air when engine is at running temperature?

 

Yea my heater works fine as well. I can't figure this out

 

wow all that work and still quirkiness.

If you have a ELM bluetooth dongle what I'd do is hook it up to an app like Torque and check what temperature the ECU is reporting if it's consistent with the Temperature gauge.

Did you Bleed the Air out of the cooling system the times you refilled the coolant? Also what kind of coolant are you running? what's the percentage of water? As a test you can always run just water or 70% water and 30% coolant to see if the car still overheats.

Did you turn on the heater core when bleeding/flushing the cooling system? That's another thing I would check if it were me.

 

I don't have a ELM Dongle but I can purchase one or what if I get a regular obd2 reader? I did bleed the system and burped I haven't had to put coolant in at all. I used a 50/50 blend from my local shop its PEAK brand (Green Coolant) I'm thinking of throwing in my new thermostat and leaving it like that until I can figure out the problem.

 

any obd reader should tell you what temp the ECU is reporting, if you have something just use whatever you got.

I think the correct coolant is the Red/Pink coolant, I get AISIN oem from my local parts store.

I think you can also use Zerex Asian, Green coolant is the wrong coolant for the car from what I've told however when the original owner of our 99 Camry V6 had the car serviced that's what they put in there. I changed it out when I did the timing belt, not sure if it really matters but all Toyota/Lexus I've seen used red from the factory.

If you install a new Thermostat, be sure to position the relief valve correctly, I believe it needs to be within 15 degrees of the Mark, if memory serves me correctly. Consult the service manual that someone posted.