wingpad

I have a 1992 Lexus SC300 with around 126k miles on it. I had the water pump and thermostat replaced with OEM replacements at the end of July. After getting the car back, it now overheats after being in extended use for 2-3 hours at LOW engine RPMs. Basically, if I pull off of the highway or drive in heavy traffic, the car will start to overheat (the temp gauge moves up towards the red but never hits it), but if I get the revs back up (somewhere around 1-1.5K RPM seems to be the cutoff) it goes right back to the middle of the temp gauge and stays there. In addition, the coolant reservoir tends to fill up (to the top) and the radiator will empty out. I'm not sure if I'm burning coolant or if it is just moving between the two but I have had to empty the reservoir and refill the radiator every time this happens. On short drives around town (with low-to-high engine duty, thirty-forty minutes or less), I do not observe this issue. It is only occurs after the engine has been allowed to get hot for sustained periods of time. As far as bubbles in the coolant reservoir goes, it seems that there are a few occasionally but it does not seem like a steady stream of bubbles.

TL;DR: Engine overheats after sustained use at low (< 1.5K RPM) RPMs but not at high RPMs, coolant fills up the reservoir. Recently replaced my water pump and thermostat but I don't know if this is related to that.

So, does anyone have any ideas of what this could be? I am planning to do a pressure test but I wanted to see if anyone had any easier tests before I forked out the 40-80 USD for a pressure tester kit. I am starting to fear for the worst, a blown head gasket, but I am hoping this is something simple. I searched around the forums but didn't really see any issues reported like this. I am hoping someone has encountered this before and has an easy fix, but that might be a lot to ask for... in any case, thanks in advance! Any insights would be appreciated

jimbosr1

you most likely have air in your coolant system.if you cant work on your car,have someone get the air out for you.also put a new rad cap.

RXRodger

iTrader: (2)

Bleed the system, give it time to get all of the air out, even jack up the front end a little if you can. Replace the radiator cap if you haven't lately as well. You would be blowing coolant at higher rpm if it was a head gasket most likely, so start with the simple and cheap stuff first.

wingpad

OK, thanks for the advice. I will read into bleeding the system and decide on whether or not I want to do it myself. The mechanic I took it to to have the water pump/thermostat probably didn't know about the specific procedures for our car and messed it up. I just bought this car in June and the previous owner didn't seem to maintain it well, so I have no idea when the radiator cap was last done. I'll probably replace that, the radiator and the coolant hoses while I'm bleeding the system and filling it with Toyota Red (right now it has green) since I have no idea when they were last done either. I'll post an update after trying that. Hopefully that'll fix it.

tjmhillz

iTrader: (6)

bleeding the system is really easy but sometime time consuming.I would recommend picking up this its makes life easier . You take your radiator cap off and use one of the ones supplied. You put the funnel on and fill half way with fluid. Start the car and watch all the bubbles come up. Then once your done you can plug the funnel with the yellow stick it comes with.

1997Soarer

iTrader: (1)

Good call on replacing the radiator. Rule of thumb is, if the plastic top is brown, it needs to be replaced before it cracks. A brand new Toyota radiator will have black endcaps. The plastic turns color with age. I don't know if Toyota designed it like that on purpose, or it was sheer luck that it turned out that way.

These cars are picky when it comes to bleeding. You need to put the front of the car on ramps, or jack it up so the front wheels are completely off the ground. That's the only way I know that works on getting almost all of the air out. If you don't have access to those, try to find a steep hill and park facing up hill. Then finish bleeding the air out there.

Returd

I assume you've checked the fan?

wingpad

Alright, well I replaced the radiator cap and the problem got a little better, but I was still observing some issues so I took it to a shop to get it pressure tested. The good news, it's not the head gasket. The bad news? I have a pinhole in a cylinder wall and combustion gases are escaping into the coolant system. So, since I wanted an IS300 more than an SC300, I think I am going to try to ditch this and find myself an IS300 to start cranking on. It was fun while it lasted but it's just not worth fixing to me. The worst part is I just had a bunch of maintenance done so I'm out $2k that I'm never getting back, ohhhh well, c'est la vie.