Yes Another Overheating

[fino]

90 ls400 it belongs to my niece. yes i have read the other post but did not help much. The car is over heating after about 15 min. I have been working on my own cars for about 30 yrs. so I know a bit about cars. I repalaced the water pump about 4 months ago, it was bad (leaking). It just started over heating. I took out the thermastat and boilied it on the stove, it opened. i left it out and put the housing back on it still overheated. took both hoses off and ran water through to see if there might be a block but the water flowed freely, so no blockage. I then turn the engine on to see if the pump would push the water out ad it did not. if I fed the water while the engine was runing it flow through. Which normally I would say the pump is bad, it is possible but being only 4 months old unlikely but possible. not having worked on lexus' I do not know if there is some thing that i do not know. she has been without a car for a couple of weeks. thank you for your help

[Malc]

Is the radiator reservoir cap OK ?

Malc

[ROYT]

If the water is not circulating, sounds like the pump is seized.

Any collapsed hoses?

[fino]

i believe the cap is good when hot it goes out the overflow hose not the cap. No collapsed hoses I was hopoong the pump is not bad it is only a few months old. I really was not looking to replacing it again. It takes a few hours to do that, but that seems like thatis all it can be.

[steve2006]

Welcome to the LOC sorry to hear of your problems.

Sounds very much like the WP Where did you buy the replacement from?

[beavisrules]

is the timing belt tension ok?. I'd have thought if the pump was seized it would make smoke (or a lot of noise at least) as the belt ran over it?.

too loose and maybe slipping over it.

might you not just try without a thermostat?

would be a lot easier to diagnose without a thermostat too as no water round the pump area (when it gets hot) would indicade a gasket/barrel/cylinder leakage.

[fino]

at auto zone so they will replace it. think that the pump is broke not so much seized but broke and that is why it is not spinnig. the fan is conected to the water pump the belt truns at that point and the fan is spining fifne. I was sure it was the pump, just not having done any work on lexus I was hoping it was some thing else. I was not looking forward to spending most of 1 day replacing it again. They are not the easiest to get to.

Thank you all for your help, I gues I know what I am doing this weekend.

[fino]

Ok so it was not the water pump. Now it was mentioned about the overflow cap was leaking, I am not positive. how ever the guy that replaced the thermastat craked the housing. Some one also mentioned burping/ bleeding the system. Dose this mean for the water pump to work it has to be a seal sytem? I am sure the guy did not bleed it to make sure it was full with fluid. All the vehicles I have worked on I could leave the radiator cap off andd see when the thermastat opened and watch the water flow. So does it need to be sealed if so that would be why it was not working when I had the hose off and no water was being puhed throught he engine.

[ROYT]

If the water isn't circulating with the thermostat out, it still looks like the impeller on the pump is not turning

[fino]

tha is what i was thinking also but i took the pump off and indeed it does turn. the belt was on fine, while the pump was still on I turned it by hand and could see the water going back into the engine so it seems like the impeller is working. Now it pulled the water in but when i turned it so as to pull the water out it spun but would not pull th water out. Which is the way it should when th e car is running but i did have it apart so there was not a whole lot of water in it