MKIII Heat Issue

[Ryan]

The car is a 1987 Toyota Supra N/A with only 65k original miles

I live in Michigan and I have been having problems when i take the supra out with the heat not quite working. What I mean by not quite is that I let the engine warm up to normal operating temp and then while im driving it I turn on the heat and fan all the way up to 85 just to get some heat flowing. The problem is that i feel the fan blowing but the air is still cold. If I push the car harder and into higher RPMs the air coming from the vents becomes hot like it is supposed to but only when the engine is at about 3500 RPMs or higher. After about 45 min to an hour the air from then vents actually becomes normal and starts to warm the interior of the car without being at high RPMs. The entire time this happens the engine temp gauge never changes.
Any ideas as to what this might be?
Thermostat? Heater core?

Thanks in advance for any of your responses

-Ryan

 

[lewis15498]

Not gonna be a sticky thermostat, Id check your heater control valve before I started digging for a heater core.

 

[Ryan]

anyway I can do that with my limited knowledge without taking it to someone?
Ive taken off the the center console and stuff to get to the shifter bushings before and can do most stuff if directed well

 

[lewis15498]

Did you check your heater control valve? Its in the engine bay on the firewall, not in the dash.

 

[Ryan]

pictures?

 

[CRE]

Here's a pic of the VSV and actuator/diaphragm:


Here's how to bypass it:


Bypass the VSV and diaphragm and see if your heat is restored.

 

[mercuryfreak200]

is that by the vacuum canister??

 

[CRE]

If you mean the charcoal canister, yes.

 

[supraman7mgte]

if the vsv is dust,you wont get any heat at all.it controls the valve that diverts hot coolant to the heater core

 

[GotBoost?]

Yes, it's a common issue, those valves fail due to old age. Get a new one. In the meantime, IIRC, if you switch the vacuum hose to the other side of the valve, it defaults to heat right away. FWIW

 

[S.A. supra]

I would let the car warm up and pop the hood and lift the lever on the bottom side and manually open the valve the heat woulds stay on till the car cooled completely. Or you could just buy a new one or get one from the junk yard. I bought one from the junk yard for $8 for my bro in law.

 

[CRE]

if the vsv is dust,you wont get any heat at all.it controls the valve that diverts hot coolant to the heater core

True, if it's completely shot the valve will never open; But they can fail in such a way that the problem is intermittent... my last one did. A bypass is a cheap and easy diagnostic as Lewis mentioned.

 

[mercuryfreak200]

yes i meant the charcol canister. sorry my bad

 

[Ryan]

First off I was unable to check the heater control valve yet but there is a new development. I started the car and drove a very short distance to the ATM and the car had just started to heat up. While sitting at the ATM I noticed that the temp gauge started climbing and was suddenly higher than normal and then went right to the top. I wasent sure why but noticed that the air blowing out of my vents was still cold. I gave it a few hard Revs up to 5500 and then the temperature started to drop back to normal and the air blowing out was now warm. any sugesstions? possibly a fan not starting?

 

[Supraflymk3]

Is your exhaust blowing out white smoke?

 

[YoungGunSupra]

yup check that valve. when i had my heater core replaced because of a blown hose...the rubber practically dissolved in my hand as we took it out..

 

[GrimJack]

First off I was unable to check the heater control valve yet but there is a new development. I started the car and drove a very short distance to the ATM and the car had just started to heat up. While sitting at the ATM I noticed that the temp gauge started climbing and was suddenly higher than normal and then went right to the top. I wasent sure why but noticed that the air blowing out of my vents was still cold. I gave it a few hard Revs up to 5500 and then the temperature started to drop back to normal and the air blowing out was now warm. any sugesstions? possibly a fan not starting?

Sounds like more than one thing wrong.

Check the valve that everyone has mentioned, this should take care of your heat inside the cabin issue.

As for the heat climbing on the gauge, first things I'd replace are the thermostat and radiator cap, both are cheap and easy to do. Cut the jiggle valve off the thermostat, and make sure you mount it with the hold from the jiggle valve on the top.