on this 77 wagon, temp guage shows low temp no matter how long the car runs, heater will kick out warm air for a minute then run cool. I replaced the thermostat, not with an oem one but with a 195 degree one from car quest, no difference at all. It seems like the engine is just not getting to temp. I will put a temp. gun on it when I can borrow one, but assuming the thermometer is showing correct on the guage (about 25% from the bottom), what gives? any ideas?

I know you said you replaced the t-stat, but it totally sounds like a stuck open t-stat. Was it new, or used; the replacement?

it was a new 195 degree t-stat from car quest. I know everyone says don't use anything but an oem t-stat, but I couldn't get one in this instance.

Can't really go by the dash gauge, they vary to much between vehicles.

 

For example, my White '86 BRAT ran around the 1/4 mark, and the '85 BRAT is just below 1/2. Both have(had) new radiator, waterpump, T-stat, hoses, along with heater core flush.

Shot the '85 with a temp gun as I thought it was running to warm. Don't recall actual reading now, but it was "normal".

 

After doing all of the above parts on the Brown '86 BRAT I had, I could watch the T-stat open/close by looking at the dash gauge, if it was below 0*F outside. 1st time seeing that was a bit freaky, as I was on my way to work and out in the middle of no-where.

 

I would suspect a clogged heater core for the low heat output. Having warm air then going cold air is typical sign of core issue.

how do you test a core to see if it's clogged? Can you disconnect hose in the engine bay, pour water in one hose and see if it comes out the other?

get a oem thermostat from the dealer and you will have good heat again.

how do you test a core to see if it's clogged? Can you disconnect hose in the engine bay, pour water in one hose and see if it comes out the other?

 

Start the engine and let it warm up to temp.

Put Heat Selector to it's Hottest setting, turn blower to High.

Pop the hood and feel the heater hoses;

There should be a slight temp difference between them..

If the return hose feels much cooler then the supply hose, your core is clogged.

 

The heater core is a smaller version of your radiator, so to speak.

Air going thru the fins pulls heat from the coolant to warm the cabin.

If the coolant is restricted by built up crud, it stays in the core longer, thus being cooled more by the air passing the thru the fins.

 

It may be possible to just reverse the supply/return hoses under the hood, to flush it out. Works on occasssion.

A garden hose held to either of the hoses can flush it out also.

 

Just don't attach the garden hose solidly. You can cause damage to the core by over-pressurizing it. 13-15psi system vs 40+psi house pressure.

 

You will want to swap the garden hose between the 2 heater hoses anyways to aide in flushing debris out. Allow the water to flow for a couple minutes, then hold the hose to the other heater hose, swap it again, and again.

 

Hook the heater hoses back to the core, fill system, start engine & warm it up, check heater output.

Hopefully, it worked, and you have good heat. Changing out the core itself is a P.I.T.A. job. BT-DT!!

Edited February 12, 201214 yr by TomRhere
Proof-read failure.....

thanks Tom! I know what a PITA it is to swap cores, I've done it twice before and I am hoping to avoid it in this instance.