I just bought an '81 240 2dr with some issues ( a little rust, pulls to the left, rattling muffler) but the first problem I decided to adress was the lack of heat. Driving it home from the seller's house, the heat was lukewarm at best and the temp guage barely moved. Found this forum, did some searching, and decided to replace the thermostat. Sure enough, old one was stuck open. Installed new thermostat and gasket, but didn't change coolant even though it looked a little brown. (No garage to work in, and it's cold out there, so I did it quick and dirty.) Now when I drive the car the temp guage rises to 9 o'clock in a few minutes and stays there. When I turn on the heat, I get wonderful hot air, but it only lasts about 30 seconds and then turns cold. If I shut off the fan and wait a few minutes and then turn it back on, I get hot air again but only for another thirty seconds. What do you think? Air in the system? Clogged heater core? Heater valve? Thanks in advance for your replies.

Thanks for all the replies. The heater works much better now. I think there was an air pocket in the system which took itself a while to work out. The new thermostat I installed didn't have an air vent. However, I am getting some fog on the inside of the windows, and the pass. side carpet is wet, so I may have a bad heater core after all. Thanks again. Nice forum. I'm sure I'll have more questions in the future.

Congratulations on your purchase!!!!


That seems to me like a flow obstruction, only a small amount of fluid is circulating through the core. It could be the valve or the core, to make sure you'd have to inspect the valve, and make sure it is passing fluids.

It would be wise to change the coolant and do as Jorrel says and refill with brand new coolant. I find that if you fill the radiator from the top hose it will really cut down on any air pockets.


Merry Christmas!

You probably have a large air pocket in the cooling system due to it being underfilled. Make sure it is full of coolant and add if needed.

jorrell
--
92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

When you change the coolant:

1) Make sure the heater valve slider control is fully open before draining coolant.

2) Be sure to verify that the thermostat is installed with the small hole at rim positioned correctly - at the high spot. Pop it off to check.

Small hole at rim of thermostat, with jiggle pin in hole, is an air vent. The thermostat housing positions the t'stat at an angle. The hole belongs at the high point, this lets any air or steam pockets vent upwards through the hole.

You'll see that from there bubbles will rise to top of radiator and then out the small hose to the reservoir. As long as that path is not blocked with old crud the system usually vents any air very well.

--
Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.

I think you might be new to these 240s.
Anyway, coolant flushing is a bit different from what you might expect.

Heater hoses are nearly inaccessible, located in the firewall near the tranny and engine oil dipsticks. So you can forget about a "T" fitting there for a traditional forced flush.

I think most folks just yank off the lower radiator hose and let the stuff spill. You can see that lots stays in the block that way.

Radiator has no petcock (maybe some aftermarket ones do). However there's a drain petcock on passenger side of block, about as low down as the oil filter is, but near the rear. At 3rd of 4th cylinder. It's brass. You can turn the outer smaller hex with a wrench. Likely it will come out before any fluid flows as they are usually clogged, then you clean it out. I like to use a bit of soft pvc tubing (5/16 or probably 3/8" i.d.) on the nipple to carry fluid to a container. Inner larger hex attaches it to the block. Fluid will flow very slowly if reservoir cap is on tight, flows better with cap off.

I avoid yanking on the radiator hoses especially where they connect to the rad. Radiator necks are plastic. They last for decades but a cracked neck is often what kills off these radiators. So that's why I drain at the block petcock rather than pull off a hose.

So -
Heater valve open.
Engine cold or run just a minute or two, not hot.
Prepare a water source to replenish water as you drain it (garden hose if not frozen).
Drain fluid from petcock and close petcock.
- Remember it's brass, don't overtighten.
Remove thermostat and its ring gasket.
Replace t'stat housing medium-snug without t'stat.
- It will not have a really good seal but this is temporary for flushing only.
Fill system with water.
Start engine and let it idle.
Remove reservoir cap.
Reopen petcock for a moderate flow.
Top off fluid from garden hose as reservoir level goes down.
Do this till fluid flows clear then a couple minutes extra for good measure.
Drain water, add 5 qts anti freeze, then top off with distilled water.
Replace thermostat and gasket.
Idle till t'stat opens, then top it off and button it up.

Even when fully "drained" there's still a good quart or two in bottom of block due to the hose layout. That's why I add 1/2 the system capacity of antifreeze (5 qt) when it's as empty as I can get it. Then add water to top it off. If you premix the antifreeze you'll never get it all in, as you're starting with a couple qt plain water in there already.
--
Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.

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