Overheating but not really? Air in system or other problem? Need help diagnosing (Page 1/14)
cebix OCT 31, 03:34 PM
Well I had this problem before and I though it was the head gasket. Now that the engine is rebuilt and the cooling system has been flushed and the problem remains I'm thinking major air bubble but I hope somebody can help me pinpoint the problem.

I've got a new water pump, new tstat, new correct rad cap and new correct tstat cap. The tstat doesn't sit very sturdy though in the housing, it seems to be sort of loose in there.

The problem is the temp gauge rises VERY fast while idling after initial warmup. But just a little rev and it goes back to the second mark in 2 seconds. On the highway it pretty much stays dead on the second mark but just a short stop and it rises very fast to almost red. Even the idiot light blinked on me for a second but revved the motor and it's all good for 10 seconds.

The heater is set on max and it doesn't heat the cabin very good at idle. But when I rev the engine or keep it at ~1200 rpm now I get proper heat in the cabin and engine temp goes back to the second mark. Let it idle and cabin goes cold and engine goes hot... My overflow tank also spilled some coolant on the ground seconds after engine shutdown.

What can I do to diagnose this? Been trying to burp the system via old threads and Ogre's cave. Haven't yet to try to burp the heater itself, maybe there's the problem.

Any ideas? Many thanks.

[This message has been edited by cebix (edited 10-31-2019).]

theogre OCT 31, 03:37 PM
See my Cave, Coolant Fill but already read that.
Crush pipe(s) or block anything can still cause this.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 10-31-2019).]

cebix OCT 31, 03:39 PM
Yeah I read it and basically did the whole thing... except burping the heater itself. Will try it tomorrow morning and see if it helps but looking for other ideas in the meantime.

EDIT: I can't see one thing though. Should I burp the heater with the engine running or not? Hot or cold?

[This message has been edited by cebix (edited 10-31-2019).]

claude dalpe OCT 31, 03:50 PM
Check if your water pump has enough flow maybe the impeller is no good .
cebix OCT 31, 03:54 PM

quote
Originally posted by claude dalpe:

Check if your water pump has enough flow maybe the impeller is no good .



Would that still apply if giving the car some revs will get the temp down and it does stay cool on the highway?
theogre OCT 31, 04:19 PM
Depending on weather... Standard T-stat can often behave like that but shouldn't turn on Temp light. (Tstat isn't design to be full on/off instantly but many are too fast to open/close and in cold weather can slam the engine w/ cold coolant.)

bleed heater likely isn't your problem if you follow direction in cave.

block intake manifold output pipe/hose to heater maybe

Heater core and/or radiator can be very blocked and still fill the system w/ about same amount of coolant.
All it takes is to block very small sections of them to stop coolant flows down many tubes. Or tubes are heavily coated w/ crap and "rust" causing little heat transfer to air.
Might see block tubes w/ FLIR, Cheap IR temp, etc. Start at D side and look for cold tubes relative to D side tank and other tubes at same distant from D side tank. All radiator tubes should be close to same temp at ¼ ½ ¾ of total distant between tanks.
Might see block tube at bottom of either using a cheap bore scope w/ mirror tip to look into them. (Empty the rad before trying this.)

Bottom tubes are more likely to block then upper tubes because how both slows down flow in them on the way to their outlets. Too the point top rad tubes you see thru fill port may look new and bottom in completely block in them and/or in D side tank.
Block tubes may not care when you flush them ether. It depended just what is blocking them and often how you flush.

Bent pipes are crush pipes. Small bending can hind big blockage.

[This message has been edited by theogre (edited 10-31-2019).]

cebix OCT 31, 04:22 PM
So you're saying my problem is less likely air in the system but more likely a flow obstruction? The rad is old, yes. I was told it was flushed during engine rebuild but who knows. Two of my previous t-stats wouldn't open when dropped into boiling water. One had a little hole drilled out and it seemed to work the best as in slowest temp creeps but also a longer time to get up to temp during cold starts.
Spoon OCT 31, 05:09 PM

quote
Originally posted by cebix:

I've got a new water pump, new tstat, new correct rad cap and new correct tstat cap. The tstat doesn't sit very sturdy though in the housing, it seems to be sort of loose in there.
Any ideas? Many thanks.




I'm sure you know there's suppose to be an O-ring on the T-stat, right? And it should fit snug in the T-stat bore. If not then you may be bypassing the stat to some degree.
Everybody covered the basics so you have to look deeper. I had those same symptons on a non-Fiero and it was a partially clogged radiator. The coolant was taking the path of least resistance thru the radiator. Goose the gas pedal and the heater gave warm air and temp gauge would drop.

I pulled the radiator and took it to a professional radiator shop. They dropped what they were doing and hooked the radiator inlet up to what looked to be an 1-1/2" hose & pump and threw a switch. With just a visual of the discharge flow he knew the % of blockage. When I went back to pick it up he gave the same demo and even I could see a huge the difference.

That radiator was from 72 Dodge van V8 and it was worth cleaning. The aluminum stuff they make today it's probably cheaper to replace it with a Champion if a flow check justifies it.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

cebix OCT 31, 05:30 PM
Yes, there is an oring. I think the shop might have polished the tstat housing inside a little too much, the thermostat isn't as snug as I remember it to be before the rebuild. Anyway bypassing the tstat a bit I guess basically contributes the same thing as drilling a little hole in it? I guess it shouldn't cause these problems and the car gets up to temp very quickly on initial startup and the temperatures here (~32 degrees Fahrenheit).

I'll try to burp the system some more tomorrow as I still see coolant needs to be added after cooling down (no leaks found). If that doesn't get me anywhere I'll look at the radiator. Thanks.

[This message has been edited by cebix (edited 10-31-2019).]

theogre OCT 31, 05:59 PM
If everything is in good shape...
If you just fill the system, often takes a few heat/cold cycles to remove all air out regardless of "Burping" methods posted here etc.
Even fill w/ cave method can trap air for days to allow system to do it's job pushing air out.
Tstat may act "weird" while system purges itself of air too.

And that's if the overflow tank and tube and rad cap are good and sealed. They may not leak coolant out but any air leak will suck air back in when cooling after engine shutdown.

But Sadly is possible for above reasons...
Flush a rad is a electric circuit. Most water flows where is easy to do so.
Block tubes are like big resistors that flow very little to nothing.
Radiators and heater cores in a car, heavy crap often sinks to bottom and often stays there even ignoring corrosion problems hard blocking tubes.

Could try to take it out of car then put water in both side taking turns. Warning: If car is auto trans keep water out of oil cooler or you have big problems "drying" the heat exchanger guts. Water get in the trans will cause big problems even wrecking that.

If you try flush products...
Some times flush products helps but often doesn't. Worse some might "wash" crap away that's sealing weak/leaking tubes.
Some products eat aluminum parts so can't use most strong flushes. Most of these should have warnings that say so but don't know labels where you are.

So If you can get tools above so can see inside of both tanks, look at temps across the rad, etc. might save you headaches trying to flush a "dead" radiator.
That's assume either tank isn't dying w/ cracks starting etc like in my cave. If you see small cracks is likely time to get a new one soon. More so w/ D side because gets a lot hotter.

Flushing heater core is about the same but ½ of tubes flow in opposite direction because inlet and outlet is on same side.
But is small so could try flushing both directions in the car w/ a water hose and a extra hose so wast water get out of car.