Overheating but not really? Air in system or other problem? Need help diagnosing (Page 12/14)
cebix DEC 17, 02:25 PM
So took the heater core out, made a bypass tube from a copper fitting.

Ran a test drive, no leaks, all hoses hot.

...and the temperature doesn't now fluctuate so much, pretty much just a steady overheating condition, and giving it gas doesn't help much anymore in terms of cooling. The fan even came on when the gauge was showing a little above 220 when it wouldn't engage before until heat soaked engine start and it did it while driving steadily at 30 mph.

Also the reservoir level didn't move one bit, just a slight "burble" after engine shutoff so I know the hose is flowing because I could see the coolant in the reservoir bubble up a little when this happened.

I know, I haven't taken out the radiator yet but wondering if this gives any clues to anyone... Why wouldn't the reservoir level change?
Patrick DEC 17, 02:49 PM

quote
Originally posted by cebix:

The fan even came on when the gauge was showing a little above 220 when it wouldn't engage before until heat soaked engine start and it did it while driving steadily at 30 mph.



I don't know what's going on with your reservoir, but there's obviously still a serious cooling system issue for your rad fan to be coming on "while driving steadily at 30 mph"... especially in December!
cebix DEC 17, 03:16 PM
It's just weird that this came up after bypassing the heater core. There was some "rust" crap in the core so there's definitely some stuff circulating. Maybe there's an air pocket after removing the heater core. Going to drive around for a bit like this and see where it goes.

EDIT: The coolant level in the tank dropped overnight from half full to just below add. Filled it up to half full. Drove to work today and NO overheating whatsoever. And the hot level got up to almost full so maybe, just maybe it was the heater core all this time? Maybe now it's just a matter of burping itself?

[This message has been edited by cebix (edited 12-18-2019).]

cebix DEC 19, 02:55 AM
So maybe it's a little early to be certain but I think it's solved.

It was a clogged heater core.

Apparently I did a crap job at flushing it the first time. This time after a few days of random flushing while waiting for the new one this came out of it:



No overheating whatsoever with the core bypassed. Gauge moves fluidly and goes up normally. Thank you guys very much for your help.

Anyway, is it a good idea to just put in the new heater core when it arrives or should a radiator flush be done prior?

[This message has been edited by cebix (edited 12-19-2019).]

olejoedad DEC 19, 09:10 AM
I would flush the system again. Maybe a couple of times.....
Patrick DEC 19, 08:41 PM

quote
Originally posted by cebix:

So maybe it's a little early to be certain but I think it's solved.

It was a clogged heater core.

No overheating whatsoever with the core bypassed.



Unless the added coolant pressure, due to a plugged heater core, was somehow preventing the thermostat from opening (I don't know if that's possible), the heater core has little to no bearing on coolant temperature. I suspect you're going to have continued problems until you properly deal with the radiator. It no doubt has the same crap in it as the heater core had... probably a lot more of it.
cebix DEC 20, 02:15 AM
You're probably right. I'm also now doubtful of flushing since it looks like it's not easy to get right and I doubt a shop will do any better and probably charge me more than a new radiator is worth.

Are there any specifics in the new Fiero radiators? I have an '85 2.5 automatic with AC. Do they all come with transmission coolers? My only real option because of shipping costs is a Spectra Premium CU828 from Rockauto which seems to say it's a universal fit but I would like to ask you guys for an opinion first. Thanks.
Patrick DEC 20, 04:05 AM

quote
Originally posted by cebix:

My only real option because of shipping costs is a Spectra Premium CU828 from Rockauto which seems to say it's a universal fit but I would like to ask you guys for an opinion first.



The only mention made of this part number in the forum is Here. Seems like it should be okay.
cebix DEC 20, 06:59 AM
Thanks. Going back to your pressure buildup thinking - I think that might explain the sudden overflow of the reservoir after engine shutoff. And the pressure probably was what blew the heater core finally.
cebix JAN 12, 05:29 PM
All right... Installed a new heater core and radiator. Flushed the system, burped it per Patrick's instructions... And it ran like a dream! Like a new car should. Steady gauge, all that. Sure enough I was happy it's solved.

That was yesterday. After cooling overnight I noticed the reservoir level didn't drop. So I took the rad cap off (maybe shouldn't have done that?) to see if the hose is flowing. It is. I'm wondering if I might have messed up the burping by removing the rad cap and introducing air back to the system. Is that possible? Looking for probable cause as a rad cap failure at exactly this time seems not that likely to me.

Also the "old" symptoms started creeping in back today, gauge starting to fluctuate at a standstill but not even reaching 220. Would go down rather quick after revving up and staying firm at highway speeds at the second mark.

[This message has been edited by cebix (edited 01-12-2020).]