Slight overheating

[ShadowFromHell]

Im having some problems with my 87 NY slightly overheating. It is slowly oscillating between 190 and 210. I checked that with my OTC 2000. Has a 180 thermostat and its 20 degrees outside.

I had to pour some stop leak in it last week. Now my heater core seems to be severly clogged. Even with it hot its taking a good 10 min before Im getting any sort of heat. Ive read if you just block the heater lines it can cause this issue since those lines are the thermostat bypass. Could it be so clogged its causing this? My other thought is the radiator, but IME when its this cold even a poor T2 raditor would be fine. I have a fullsize v6 raditor in this car.

Im going to blow it out asap, but am curious if this is my issue or if I need to keep looking.

[shackwrrr]

does sound like "thermostat bounce" exaggerated by the clogged heater core. Get some CLR and flush out the heater core with it.

[4 l-bodies]

Saw that coming from about a mile away. Yes, without a functional bypass (heater core plugged) the vehicle will have more exaggerated temp swings when the thermostat opens and closes. You can check to see if temps stabilize and run normal again by putting heater control on defrost or max AC and cold. That will bypass the heater core at the control valve. Add heater core to your list of things to repair when you get to your tools, and put Stop Leak on the do not EVER use list. If your lucky, you may be able to get some function back of heater core by back flushing it several times.
Todd

[GLHNSLHT2]

Don't ever use CLR. If you want to see what it does I have a water pump and radiator to show you the crap it left all over my cooling system.

[dwh4784]

Yeah, I used CLR and even after flushing it out numerous times in both directions before reconnecting the heater hoses to the rest of the system I lost my radiator within days. It did fix the heat though! But I wonder how much it would have improved with just water or a Prestone coolant flush or something like that. I flushed a lot of nasty brown gunk out of that heater core, but again IMO I wouldn't use CLR ever again. I should listen to Jay more often, he told me not to use stop leak either and boy what a mess that stuff made. I flushed it all out of the bottom of the block when the head was off, looked like I was mining silver in the drain pan.

[tryingbe]

Stop leak is probably one of the worst automotive products out there.

People still use it hoping for a "quick" and "easy" fix, not realizing the only things the stop leak will for sure plugged up are the radiator and the heater core, which will cause the repair bill to be bigger at the end because there are more parts you'll need to replace. Worst, stop leak can remain in the system and plug up the new radiator/heater core as well.

If I remember correctly, A.J. refuse to work on a car with stop leak in its coolant system, because of liability/warranty reasons.

[GLHNSLHT2]

I should listen to Jay more often, he told me not to use stop leak either and boy what a mess that stuff made.

You can lead a stubborn a$$ to water but.............

[ShadowFromHell]

I used stop leak as a last resort. I was 150 miles from home and out of options. It did its job and got the car home where I could properly fix it. Even before the stop leak I wasnt getting much heat. I think ive got it all out now but for some reason this motor was full of rust.

I just flushed the heater core and it was very obvious that it was clogged. Knocked a bunch of rust out of it and got it flowing good. I started getting heat at 2 bars (didgi dash)!

Ive got another question, is the diverter valve opened or closed with vacuum? Ive got a vac leak in the HVAC system. I would think it would be designed to fail open but you never know.

[GLHNSLHT2]

glad you got it home.

[ShadowFromHell]

Drove it some today and it isnt overheating at all. Best of all I have HEAT!

[GLHNSLHT2]

Nice.