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Air In Cooling System


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Hi All!

Newbie here with a a 1993 Lexus GS300 with 100K on the clock. The other day, the engine temp started to bounce up above normal. When it cooled, the radiator was low a couple of inches so I topped it off, and the reservoir was normal. I ran a pressure test and it was fine and solid at 16 lbs. However, the radiator cap (original I believe) had clearly seen better days, so I figured that was the cuprit so I replaced it.

Still, the system is still taking in air. After driving, the radiator is now a few inches low (getting worse, actually). It is blowing the coolant back into the reservoir (overflowing) but still depriving the radiator of coolant. I re-checked the pressure and it is fine.

Any suggestions? Do I have some blockage in the line from the reservoir to the radiator so it’s only going back to the reservoir but not recovering to the radiator?

Thanks

Jeff

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Check the engine oil quality, under the filler cap, top of the dipstick tube, for sludge. You may have a blown headgasket. It sounds like the coolant is being pressurized from combustion gases, and that's what is blowing it out. One of the symptoms of a headgasket failure. It may not be good news.....

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If it is the gasket it will get worse rapidly. The pressure check is far less than the combustion pressure so it's possible ( although not for long ) for the test to not show the problem. When the gasket lets go more it might.

On the good side it may not be the gasket at all.

Run the engine with the rad cap off (cold) and see if any small bubbles appear.

Good luck!

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Bad news here. Radiator is doing this....(not mine, but a video I found of same)

I still have no other indications of problems, althought I am observing a slight slickness to the coolant. There is no exhaust smoke, no oil contamination that I can see. I guess I'm fortunate that it appears to be only blowing out of the cylinders and not in.

Does anyone know how many hours (about) that job is?

Thanks

jeff

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The smaller the bubbles the more likely it's a crack. Gaskets will blow out enough to produce the large bubbles. I've seen a lot worse than that video....and don't allow the system to overpressure because it can burst the heater core as the cap won't vent fast enough. That would be no fun either.

The head has to come off and be checked for cracks, resurfaced if OK in a VERY good broach to factory flatness and surface finish.

I don't know the flat rate, but I wouldn't be surprised if it's about 10 hours re and re.

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OK guys, this is bizarre.

Good news is that I had leakdown and compression tests on all cylinders and it all came out good, no indication of head gasket breach or cracked head. Still not seeing any other signs whatsoever that coolant is leaking into the heads.

Mechanic pulled out entire cooling system, advised that he believed that it had been leaking at one place near the block and near the heater core (apparently not picked up by the pressure test). He reassembled the system, flush/cleaned out everything, and replaced the coolant.

I did expect to continue to see some air pockets, and over the next few days found myself topping it off a few inches on the radiator but about the same amount each day (i.e. not improving). I could also hear some air pockets in the dash when I ran the heater. So I figured I just have some air in the system (not a surprise, because I know he gave the heater core a good cleaning). I figured it needed to be burped.

First parked it on an incline with the radiator fill at highest point, but got quite a bit of splash out at operating temp and revving at 2500 RPM. So the next day, I took a 2 litre plastic bottle and cut the bottom off. I took some electrical tape and wrapped the spout so I could get a reasonably good seal around the radiator intake and filled it with 50/50, it was fine. I started the car at idle and it burped out into my funnel and I added some water, keeping it about half full. Eventually the bubbles stopped and it started to simply suck the water down and discharge out through the expansion tank cap outlet. I figured at that point it was successfully burped. Also, to my pleasure, I noted that while it was running it did not seem to be generating air...once the air in the system was purged, the bubbling stopped. That was last night.

This morning after about a 10-15 mile drive and a 1.5 hour cooldown it was down again a few inches in the radiator. I didn’t have water with me and had to make another stop, so I drove it for about 10 minutes and made my stop (about 15 minutes). It was still hot but I needed to get on the road, so I covered it with a towel and slowly released the radiator pressure from the cap. It was still low. I left the cap off and went to hunt down some water (5-10 mins)….when I returned, the level at the radiator had recovered (I assume from the recovery tank). So, I have no idea where the air is coming from at this point.

Any suggestions of what to try next????

Thank you

Jeff

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The mechanic that did the work is suggesting that my radar is simply too high on this. Told me to top it off, close it up, and drive it for a few days without checking it (but obviously keeping a watchful eye on the engine temp). He suggested that the displacement/couple inches off the top of the radiator may just be a normal function of operation and is unsure if I have a continuing problem. I will give that a try, but open to other suggestions if anyone has them…?

Thanks

Jeff

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I don't think your radar is too high - it's your car. But do fill the system, and fill the expansion tank to max. Heating and cooling will draw coolant from the expansion tank and fill the system without any further intervention on your part. Don't open the system at the rad cap any more for a few day is my advice. These systems do not require "special" treatment to purge air. It's a Toyota after all. So drive it around, and then, when cold, open the rad cap and look. If there is an air space on top you have a problem. Gasket failures, and/or cracks, will prevent the system from developing vacuum when cooling down, which is what draws coolant from the expansion tank.

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Hi SRK

Thank you for the input. I am currently doing as you said, just driving it around and watching the temp gage and carrying some water in the trunk. But I think you are correct insofar as just before I closed it up, the level was below the fins in the radiator, which wouldn't seem normal under and condition.

I agree I probably have a leak somewhere, but I don't know where to start looking next. The line from the expansion tank to the radiator is not new, but it looks OK. I was thinking of just replacing that this weekend. Maybe the new cap I got is bad? That would be unusual, but I guess I have seen stranger things. It would explain why the cooling system pressure test didn't pick it up.

I'm starting to wonder if the compression test didn't pick up a head gasket breach, but the readings were strong and given the current level of displacement it SHOULD have shown something. ALso, still no fouling of the oil (motor or tranny), no white smoke, and the coolant does not smell like combustion gas...just coolant. I really think it is just air being sucked in somewhere.

I'll let you know what happens but I fully expect to be back to square one on this within the next day or so.

Thanks again for your help.

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My concern is that a compression test and a leakdown test are measures of cylinder sealing - rings and valves, and have nothing to do with the small leaks that may pass coolant. A cooling system pressure test is conducted over time - sometimes hours - and will force coolant into the cylinder. The engine can be cranked with the plugs out, and if a spray or mist of water comes out of a plug hole, then the problem is found. That would be the kind of test needed.

The coolant has to be going somewhere, and if not seen on the outside of the engine or the ground, it's consuming it.

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Trust me, no snake oil will fix it. Remove the head, inspect for cracks, inspect the gasket for the failure point. If it's the gasket, surface the head ( use a shop that has a profilometer and can prove the surface finish is with specs, and doesn't rely on their fingernails to do so instead) and then fix the engine properly. Then you'll have confidence in the car and be able to enjoy it.

As much as it is a bummer, at least the diagnosis is clear, and the money will be spent correctly, rather than just throwing parts at it.

Good luck.

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