New Radiator Cap?

[AustinGT]

After taking care of the thermostat leak, I have noticed that each morning the overflow reservoir is almost empty. There is always the same amount in the bottom, even though I refilled it the previous morning. The car is not overheating, and there is no coolant leaking on the floor of the garage. At first I thought there were just air bubbles in the system as a result of the coolant/thermostat change, but I have refilled it four times. Since there is no leaking, the low coolant light has never lit up, and the car is running cool, I am thinking radiator cap, perhaps? The shop also said it might be a bad cap, does this sound realistic? Thanks in advance for help!

[pishta]

After taking care of the thermostat leak, I have noticed that each morning the overflow reservoir is almost empty. There is always the same amount in the bottom, even though I refilled it the previous morning. The car is not overheating, and there is no coolant leaking on the floor of the garage. At first I thought there were just air bubbles in the system as a result of the coolant/thermostat change, but I have refilled it four times. Since there is no leaking, the low coolant light has never lit up, and the car is running cool, I am thinking radiator cap, perhaps? The shop also said it might be a bad cap, does this sound realistic? Thanks in advance for help!

No. A cap that is venting too soon (bad) would not cause the coolant level to drop. Where is the water going? Could it boil out as a vapor, no, i t doesnt get over 230 with coolant to vaporize---Out the tail pipe. You may have a head/intake gasket problem. Get yourself a pressure test cap and pump it up, look/listen for leaks or check the pressure guage to see a leakdown. You may have a high pressure leak that doesnt drip when you shut down but may be dripping away while you drive. I would try some stop leak if you do find a pressure leak, cheap and doesnt hurt anything.

[AustinGT]

Thanks for the reply... I thought it could be a head gasket thing, but it only started leaking like this after the shop replaced the termostat and refilled the system. Up until then, the level in the tank was fine, although I put a little in every now and then (like a few ouces) due to the thermostat housing leak. So maybe my question should be is there something the shop could have done that could cause the leak? It drops to the same level every time... just above the line to the radiator.

[91LexusLS400]

Sounds like you might have air pockets still in there from the thermo repair. I'd just keep fill it and see if it stays level in a few days.

[cardona6569]

I had a similar problem and it was the cap. Yours probably needs changing anyway. I had that problem iwth my Lex and with a Nissan Murano changing the cap cured both. If you did not pressure test the cap when you took it out chances are it is bad. A friend of mine who is a mechanic and his cars last him over 200,000 miles, recommends that anytime you take the cap out, either pressure test it or replace it with a new one.

CPR

[pishta]

Sounds like you might have air pockets still in there from the thermo repair. I'd just keep fill it and see if it stays level in a few days.

Here is a test. remove the cap start it up, let it idle and turn the AC on, let it get up to temp and see if the fluid level has changed. I had a suburban that never kept water in ot, I would fill it up a liter a week, no leaks, 2 new caps. It had an intake leak that drew water into the intake and vaporized it effortlessly, never saw steam and always had clean plugs!

[SKperformance]

It is your cap , had it happen multiple times and the new seal on the rad cap stop the fluctuation.

[AustinGT]

Well I put in a new cap yesterday, and so far the level for the most part has held. I had to add a tiny bit, but there is nowhere near the loss there was before. So, knock on wood the situation is under control! Will definitely be keeping an eye on it for a while, though..... Thanks for the input, guys!

[pishta]

It is your cap , had it happen multiple times and the new seal on the rad cap stop the fluctuation.

OK, that puts my thinking to shame. Educate me, where does the coolant go in a sealed system? Dos it escape as vapor in a weak/leaking pressure cap? And how does it get to vaporization temp when the stat is under 230+? Im open minded on this.

[pishta]

duplicate.....