My heater used to work great. Now it blows but its not hot. I notice my temperature gauge never hardly goes up, most of time stays below the bottom. Coukd this be my thermostat? Also just had my engine rebuilt...could it be something that he forgot to hook back up?

You need a new thermostat.

Thx man...love that celica!

Sorry, I was definitely driving to work and I'm not a morning person. It sounds like your thermostat is stuck open, so the engine can't get up to operating temperature and you won't have any heat.

I'll be sure to pass the compliment along to the wifey. She always loves to hear kind words.

You don't think they could have installed the thermostat backwards in the housing do ya?

That would be rather difficult, since the thermostat is about two inches long and the bulge in the water inlet which holds it is only half that high. And on a 7AFE particularly the thermostat would have to be installed at an odd angle which should prevent the neck from sealing to the block.

Easier explanation is that the mechanic who rebuilt the engine forgot to install a new thermostat (should also be installed with a new gasket), or else the thermostat has failed in the open position.

However, I find myself wondering if that's not the only issue. I had a thermostat get stuck open, and it was noticeable from the way the temperature gauge would dip with speed. The engine would still get up to normal operating temperature while the car idled. Is the cooling fan on the radiator running all the time? If it is, the mechanic probably forgot to plug in the fan temperature sensor switch or the sensor switch is faulty.

The coolant could be very low also. The temp sender cant read steam and if it was that low you may not have heat either.

If coolant was low he would over heat

Not always, it can be low enough to allow air in the heater core but circulate the engine and radiator.

^^^ yes if its low. it will circulate in the engine before it gets to the heater core