irax

Just recently my 91 lexus that I bought used has been overheating. Only slightly overheating too. It would go from the 3rd bar to the 4th bar and just stay there. But when I am driving and I have the heater on it would be between 3 and 4 or just all the way back down to 3. There is no coolant leak, no coolant in the oil, no coolant being burned. Since the car is almost old enough to drink and looking through what little records the previous owner gave me, the radiator and thermostat has never been changed. I figure that this could either be a faulty thermostat or a clogged radiator. So I replace both. I used a generic toyota/lexus thermostat 90916 03075 A82. And now the car goes all the way to the 4th mark and just sits there. Did I use the wrong thermostat? I have searched, and the best that I can come up with is that I should just re-burp the system one more time and burp it from the side of the radiator and the thermostat neck. A friend of mine suggested that I should check the reservoir filler cap. Has anyone else had a similar experience?

KA8

iTrader: (1)

It could be many things but good rule of thumb for thermostat and radiator is to use only oem units.

RA40

iTrader: (6)

Check between the A/C condenser and radiator for debris. I clean mine out each year of leaves, bugs and other grit that accumulates.

crx08

did you fill from where the thermostat sits? there might be air in the system. What kind of coolant did you use?

97CE LS400

poss. air bubble

irax

I'll try burping the system one more time

Like I said I already replaced thermostat and raidator

I didn't fill from where the thermostat sits, I filled from the resivuir. But when I burp it this time Ill fill it from there.

hypervish

You should fill the coolant from the radiator cap, when it's cold of course. Then start the car with the cap open (be careful, coolant may splash) and fill more coolant as the air bubbles escape, then get in the car and rev it a little (not much, or else it'll splash) then fill up some more coolant... Then take it for a drive and get it up to operating temperature so that the thermostat opens up... Then the next morning (or when the car is cold once again) check the fluid level in the radiator AND over-flow bottle. If it's full, your good to go, and the car should not overheat.

PureDrifter

iTrader: (10)

actually if you guys want to avoid air bubbles you should fill from the filling point on the top of the throttle body, (i believe its in the same place for the 1st gen, or close by there anyways) and not from the rad. overflow.

irax

between my radiator and ac condenser was cleaned when I replaced the radiator.

The thermostat is a toyota/lexus 82c thermostat

I burped the coolant from behind the thermostat and from the side of the radiator.

still it is at 4/6

RA40

iTrader: (6)

Just to be clear...you burped the system with the reservoir cap off with the engine at running temp? Turn the heater on also?

irax

yup yup and yup

fans turn on fine

The previous owner used regular anti-freeze and it worked fine since we bought it. So I used fresh anti-freeze since I already had some in the garage. I think the water pump might be on its way out so I'll replace that and reflush it with dex-cool and see how that goes.

3UZFTE

Wait.... Before you start just ripping it apart. Are you sure it's actually overheating? Just because the gauge reads hot doesn't mean it is. The previous owner of my LS just unplugged the engine temp sensor because it would raise and fall with engine speed, needless to say the gauge wasn't accurate. Personally, if it never jumps over the 4th mark, it sounds like it's maintaining a temperature. If it were to hit the 4th mark and keep crawling, I would be a bit skeptical, but since after you replaced the rad and thermo, your getting it to stay at a certain temp, you need to find out what that temperature is by using a inferred temp reader, their like $20. If it's around the same temp of the thermo, 180-200*, not exactly sure what temp your is rated to, but if it doesn't go over the mark, I would almost put money on is that your gauge is giving you an off reading as opposed to actually having an issue.

Does it ever jump over the 4th mark? Do you lose coolant/burn it off? Have you pressure tested your system, because the naked eye won't spot a small pressure loss once it gets to op temp. Most places that can pressure test your system can pressure test the cap as well.

My thoughts... Don't spend 4 hours doing the WP if you aren't exactly sure that it's going to solve your problem. The water pumps are pretty durable and I would imagine you would be overheating if the pump wasn't keeping up. I would bet that there isn't a major issue, but it appears the gauge or sensor is reading off, of you have a pin hole leak which is causing your coolant to slightly raise it's temp. Either way, you should have it pressure tested.

FYI: The bumping screw is above the thermostat housing. I believe it is a 17mm shoulder bolt, and should be cracked open a smige to allow air to get out when bleeding the system, hope that helps. Here is the bolt on top of the thermo housing.

python

iTrader: (4)

if ur gonna flush the system out completely i would stay away from dex-cool or toyota red...i would put in green or zerez G05. unless u plan on doing a flush every other year or 25-30,000 miles
here is the ingredients of the toyota red
85-90% Ethylene Glycol
less than 5% Diethylene Glycol
less than 5% hydrated inorganic acids and organic acid salts
less than 5% water
the acids eat away ur gaskets and seals if left in too long

irax

well it used to stay at the 3rd mark all day long, and the temp would drop pretty quickly when the car was off. It also took a while to heat up to temp too. So I see how it may be the temp sensor or the gauge, but when it first started to over heat I would turn on the heater and it would go back to 3 and be just fine or depending on the day or the road it would float between 3 and 4. And now it heats right up quickly but it just stays at 4 no higher, no lower.

deanshark

You probably have a 195* thermostat which, in my opinion, is too high. I even think the 180 is too high but that's what it's supposed to be. The easiest way to check if your water pump is working and your t-stat is opening is to take out the 17mm bolt on top of the t-stat housing (the one that you burp the system with) and see if the coolant is flowing. Of course it has to be at normal operating temp for the t-stat to open. If it's not flowing, I would change the t-stat first. (Even though it's new it could be bad)
Like 3UZFTE said don't just go ripping out your WP, more then likely it's not that.
Also the sensor in the pic above is not the sensor for your gauge. (just incase you didn't know that) it's the one behind that one with one wire.