Rod Underwood

A dumb question, Is the heater valve behind the engine OPEN when the heat is on or CLOSED. Mine is currently open - water can pass through - but I'm not getting heat??? It makes sense that it would be open to allow hot water in, BUT the default - without vaccum - is open which makes me wonder.

Thanks,
Rod

the flyin' scotsman

It should be open with the heat on and yes it defaults open.

The HVAC system supplies vacuum to close the water valve. If you've no heat hows the other parts of the coolant system?

Rod Underwood

Hmmmm. everything else seems to work fine, just no heat and now is not the time for that. Got to drive to Detroit in a week and it would be nice to have heat.

Rod

dprantl

Do you get heat if you rev the car to 3k RPM and hold for 20 seconds?

Dan
'91 928GT S/C 475hp/460lb.ft

lrpman

MIGHT not apply to these cars but on my Mercedes I had to BLEED the air out of the system to get heat. Then it was working fine. I just took the hose loose on the return side of the core and let it drip, DID NOT remove the hose just got it to leak then tightened the clamp back.
I looked in the manual and it said nothing about bleeding the system so take the hint for what it is worth.

Mrmerlin

928 is a self bleeding system no need for any special procedures . Note the hose on the top of the radiator and the top of the water bridge.
To fill the system simply remove the cap let the car warm up make sure the bottle has atleast half full , put on the cap, then drive the car for about 5 miles then park it and let ot cool off top up as necessary

j.kenzie@sbcglobal.net

Could be bad engine thermostat. When they fail they default to a full cool position and your engine/heater water never gets very warm. Check water temp gauge.

Rod Underwood

Nope, I get a small amount of heat all the time, not enough to keep you warm in the cold, but I revved it to 3K+ and held for a minute and it made no difference. Sound like there is a restriction somewhere. The fan blows fine (replacement) but there apparently not enough hot water getting to the coil, or the air is bypassing the coil somehow.
???

Rod

Mrmerlin

how old is the heater valve, if over 5 yo then replace it along with the short hose.
Have you verified its open while the car is running?
What are the temps at the top rad hose compared to the heater hoses use your IR gun to find out

the flyin' scotsman

Have you checked the coolant return hose? If its cool also then the hot coolant is being restricted from entering/leaving the system but thats assuming the coolant is getting hot enough.

Checking the t.stat is a good suggestion.

Rod Underwood

It's definately open, so I need to check the hose temperatures. I have an IR gun, but it's not here right now.

Thanks
Rod

jcorenman

Fingers work...

the flyin' scotsman

Too old school Jim I'd go out and grab a little snow then where it doesn't hiss very loud that where the engines coolest.

Back in the my m/cycle days we'd spit on each exhaust pipe to id which cyl was cool and trouble shoot from there............burnt my finger tips a few times

ROG100

Rod,
Are you sure your recirc flap is not open to outside ambient air.
If it is - it defaults to open when the diaphragm fails - this allows lots of cold air in to negate the heat from the heat exchanger.
Roger

Rod Underwood

No. I'm not. That's a good thought. I was running the car in the garage with the door open, so it could be getting cold air from the outside. I'll check the shop manuals to see where it is. in the meantine, is there an easy check i.e. does anyone have a picture of it and where it's located?

I did check the hose temperatures and they were low, about the same on both hoses, only about 5-10 degrees difference, so I am picking up a thermostat to put in today. If that's not it, it will be "preventive maintenance".

Rod