aprice2pay

Over the course of the past 2 years I have been dealing with a coolant issue that I can't seem to get to the bottom of. I'd say that once every 5 weeks or so, I notice my temp gauge climbing and I have to add 1/2 gallon of coolant or so to keep it in check. Because of this issue, I have replaced the radiator, 2 thermostats, all hoses, the overflow tank/fan shroud, the water pump, and the timing belt. There are no visible leaks, and I have had two independent mechanics verify there is not a head gasket issue. I am not sure what else to do/check to get this corrected?

I did some research and came across a case where a Tundra (4.3L) had coolant that was pooling in the intake manifold and was burning off slowly through the motor and wanted to know if this is even possible?

I only have 185K on this motor and I'm fresh out of ideas and extra cash to throw at this problem. Any advice/recommendations would be appreciated.

rkw77080

OK, you did not mention radiator cap. A weak spring can allow hot steam to escape into the overflow tank and out through the overflow tubing. This type of pressure-relief is very difficult to detect because it does not happen continuously.

Have you performed a pressure test on your radiator gap and the cooling system to see if they hold? The LS430 cooling system and radiator cap should hold 19.9 PSI

aprice2pay

I have not tried that yet, but I will. I did receive a new radiator cap from Lexus when I replaced my radiator, but I did not think to test it (or the old one) prior to replacing it. Appreciate the suggestion, I will keep you posted!

aprice2pay

Sorry, forgot to address the pressure test you mentioned. I did perform a pressure test, which is how I discovered the crack in the overflow reservoir. Other than that though, I did not find any other visible places where I was loosing coolant.

Bocatrip

Although quite uncommon, a head gasket can also be a culprit. When the car is cold take a sniff test out of your tail pipe for any sweet smells. There is also a test for this kind of leak.

JffGRY706

checked my coolant today, radiator full, but overflow empty. was some purplish powder around the radiator fill neck. dried up coolant I believe. getting coolant replaced is on my list, did not do it at 100,000 mile service as they replaced 2 gallons of coolant when timing belt/ waterpump was done at 90,000 mile service. now approaching 130,000 mile service. had car 4 and 1/2 years and only checked coolant twice. overflow was empty both times. I did turn on heater last week even though it was not cold here yet. I like to open up heater valve a few times during summer to circulate fresh coolant into heater core or else is sits in there for 7 months over the long hot summer.

rkw77080

The overflow reservoir is not typically pressurized to the same pressure as your coolant system, in fact, the overflow tube is open to atmospheric pressure. The radiator cap has a spring-loaded seal and a secondary seal. The spring-loaded seal allows the radiator to hold a certain "rated pressure" (19.9 PSI for our LS430). Once the rated pressure is exceeded, the spring-loaded seal allows the hot coolant to escape into the overflow reservoir. After the coolant temperature drops and pressure in the radiator decreases, the coolant is drawn back into the radiator. Meanwhile, the secondary seal prevents coolant from escaping out into the atmosphere.

The overflow reservoir is sized to accommodate the normal cycling of coolant in and out of the radiator via the spring-loaded seal. A weak spring will allow too much of the hot steam into the reservoir, and overflows out of it. Another culprit can be a bad secondary seal, in which case, every time the spring-loaded seal opens, some coolant will escape out through the secondary seal.

So normally you would perform 2 separate pressure tests. First test to see if the coolant system will hold the 19.9 PSI for, say, 30 minutes. This test will reveal any leaks through the 4 primary paths: 1) coolant leak into the combustion chambers and cylinders; 2) coolant leak into motor oil system; 3) coolant leak into the transmission fluid cooler within the bottom of the radiator; 4) coolant leak into the outside air. For coolant leaking to the outside air, depend upon the location of the leak, you may not see any physical tell-tale signs. For example, if a small amount of coolant leaks into the air intake system, your engine will burn it off without any symptoms.

Secondly, test the radiator cap to see if the spring-loaded seal will hold the 19.9 PSI for 30 minutes; then pressure up to see if the spring-loaded seal will open at or above the rated pressure; and finally test the secondary seal to see if it holds, say, 110% of the rated pressure or around 22 PSI. If your radiator cap has a bad secondary seal, it will typically leave some residue around the radiator neck.

Ask your local AutoZone (or most major auto parts retailers) for a loaner test kit that you can "borrow" - my local AutoZone has it free of charge. Be sure to allow the coolant to cool to prevent burn.

Lexusdk

I was gonna say it's probably the coolant valley plate, but I forgot the LS430 didn't have one. I know there's a water/coolant pipe that runs under the intake manifold. It might be leaking from the ends of that pipe. Possibly a bad rubber hose or o-ring. I just did a starter replacement on one not too long ago and kept a picture for reference. Have your mechanic inspect under the intake manifold with a camera scope