Lexus Repair: 93 GS300 Heating Problem, mechanic shop, vacuum system


Question
Thanks you.
Something happened again, after drving for 2hrs, all the sudden I had heat. But I only have heat when I am on the gas, once the gas is off, there is no heat again. Can you tell me why?

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The text above is a follow-up to ...

-----Question-----
Hello,
This is what I have done since last email.
- Thermostat changed.
- Water valve is working.
- Heater hose is not block.
- HVAC control box is working.

I dont know what else to look for. Could it be the heater core is block? If it is block, How to unblock it?

thank you,
Jeff
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The text above is a follow-up to ...

-----Question-----
Hi there,
I have a 93'GS300. I have only little heat coming out from the vent, if I turn the fan on full speed, the temp. drop instantly to no heat.  I have replaced my water pump, water valve and replace my coolant already. And it didn't helped at all.  Does the heating system work with any vacuum system with the engine?
Pls, help me cause is cold driving a car with no heat in the winter time.

thank you,
Jeff
-----Answer-----
Replace the thermostat. Make sure that the heater core loop is not blocked, and check the valve that lets coolant into the heater core loop opens & closes.
-----Answer-----
Then the heater core is probably blocked.

As soon as coolant exists the engine it runs to the valve. If the valve opens then coolant flows to the heater core. If the heater core is blocked, then it won't return, coolant backs up & warm coolant never gets to the heater core at all.


They are a pain to take out & inspect, let alone replace. You may want to call a Toyota dealer, or an independant mechanic shop that deals with imports (Toyota's).

Answer
Have the water pump tested ASAP! It sounds like the blades have been corroded off from a lack of coolant changes, or changing the water pump at some time.

Really, really, really! I can't stress how important it is to get that to someone that can check the water pump. It's an iron block & an aluminum head with a weak cylinder head gasket sealing them. Aluminum expands at twice the rate iron does, so if that water pump lets that engine overheat at all. It'll warp, pop the gasket & then you're out some good money!

Generally, the water pump & timing belt are changed every 90,000 miles.