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98 overheating issues

2K views 23 replies 8 participants last post by  Robmeara89 
#1 ·
I am at my wits end with this car, so any help is appreciated at this point. I was given a 98 Avalon with 238k miles. The car had a radiator leak and had been sitting for 4 years, prior to the leak it had been very well maintained and I was given the service records with the vehicle. I changed the radiator, dropped a new battery in and it started no problem. It overheated while driving it home, so I changed the thermostat. It still overheated on my attempt to get it home, but I was able to baby it the rest of the way. I change the water pump because I notice very light leakage, and changed the radiator cap to a 16lb (it had a 10lb on it).... it's still overheating.

The fans are working, it's not leaking coolant, it drives great aside from overheat, it's not throwing any codes, and there is no oil in coolant or vice versa. What am I missing???
 
#2 ·
The only things that pop up are that the temps are not sending the correct signal to the sensor reader. It could be a wiring or electrical issue. Can you track down the temp sensor and check to see if it is working, damaged, etc?

Otherwise with overheating, the block could have warped and could be causing extra stress on the cylinder walls. I've found out that just having one engine overheat can cause heating issues. Especially since you have already replaced most of the things that are typically associated with overheating.

When you turn on and drive with the heater, do the temps drop?

Can you monitor the coolant levels to see if there is a leak or if it is burning off? Any certain smells that you can think of?
 
#3 ·
I am starting to think that it could be an electrical issue but I'm just not experienced with those (especially with no code being thrown). I do know that the car has a bad temp fan sensor and I have it unplugged to keep the fans running. Other electrical issue is that the hazards and turn signals are unreliable.

I will monitor the coolant level, dumb question.... I know the boiling point of coolant is lower than that of water... the car currently has only water in the cooling system (it isn't remotely cold where I live and I only did this to make sure there was no leak or overheat before replacing with a 50/50 mix) would this difference be enough to cause it to overheat?

Also, no smells coming from vehicle... and the heater works fine... the temp does go down but not enough to safely drive the car.
 
#4 ·
Sometimes air trapped in the cooling system will cause overheating. With the engine cold, remove the cap, start it, and stand there with a jug topping it off every time it burps up a bubble of air. Do that until the engine is fully warmed up. Then install the cap.

Also check the cap on the overflow reservoir. There should be a hose on the underside long enough the end is submerged. If it's missing, the cooling system will suck air in when it's cooling down.
 
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#9 ·
Ok... so far total we have: replaced the radiator, replaced the thermostat, replaced the water pump, replaced the coolant temp sensor, replaced the temp gauge sensor, and the fan sensor (only sensor not replaced is the one right by the thermostat), we even replaced the coolant with the correct one for toyotas... we have burped the system, there are no smells, the car runs great and has full power, there is no oil-coolant leaks or mixing, no smoking.... doesn't overheat at idle... overheats any time it is driven. I'm running out of ideas. A friend claimed that it cannot be the head gasket because it has no symptoms aside from the overheating and that if we sat and burped it for an hour and it stopped bubbling by then it couldn't be the head. Any more ideas?
 
#12 ·
Ok... so far total we have: replaced the radiator, replaced the thermostat, replaced the water pump, replaced the coolant temp sensor, replaced the temp gauge sensor, and the fan sensor (only sensor not replaced is the one right by the thermostat), we even replaced the coolant with the correct one for toyotas... we have burped the system, there are no smells, the car runs great and has full power, there is no oil-coolant leaks or mixing, no smoking.... doesn't overheat at idle... overheats any time it is driven.
Curious...your replaced tstat, so when eng. has warmed up enuf to fully open it..do u see coolant moving alittle faster in rad? Also..do u see any junk in coolant? Considering parts you've thrown at it, sure got me stumped? There's an answer, so hang in there. About electrical..I'm alittle skeptical on that, but ?

btw..what is the sensor (not replaced) by tstat for ?
 
#17 ·
There are two sensors for the coolant. One is for the EFI(tells the computer the temp) and the other is for the gage on the dash. Did you replace both of them?

Also, Did you replace the radiator cap when you got replaced the radiator? I know it sounds dumb but if the new radiator didn't come with one, and the old one was was defective/swelled up, it wouldn't allow proper venting of the radiator and could cause issues for you as well...
 
#19 ·
Is there a reason you went to a higher psi cap? raising the boiling point of the coolant?
There should be two temp switches by the t-stat housing. one is horizontal and one is vertical. Both are temp detect switches.
 
#22 ·
Yeah, looking at what's on Rockauto.com, they're all 16psi.

What brand of cap is it? I wouldn't trust anything but OEM caps. Can you get it pressure tested somewhere? Some auto parts stores have testers that they'll check it for free.
 
#24 ·
Does it displace coolant ? It could still have a headgasket problem without mixing coolant and oil. Is there any black or gummy stuff on the bottom of the coolant cap ? It could be pushing combustion and hydrocarbons into the coolant system constantly making new air bubbles and pockets in the coolant system. They make a pretty cheap kit to test for the presence of hydrocarbons in the cooling system. I think carquest sells one its a beaker you put on top of the rad cap fill it with the blue or yellow solution I don't remember which color but if it changes colors then there is a compression leak in the headgasket. Hope this helps !
 
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