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Cooling System Questions


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Chasing an overheating situation. It has come on pretty suddenly and won't go away.


72 tii stock.


Fire up the car and within 10 mins temp is sitting just under red on the gauge. Assessed the wiring and seems ok.


New: water pump, temp sensor, tstat (75), ie hoses.


Lower hose to radiator never really gets hot as upper...tstat, right?! Well I replaced it new and get same cooler lower hose. 


When burping (squeezing) hoses both upper and lower, coolant level rises up to the cap brim on the rad. So I'm assuming radiator isn't plugged. I'm doing this with front end up on rhino ramps.


I'm not losing any coolant. Car runs fine. No smoking out the tail pipe. No milky coolant or oil that I can see. No bubbles in coolant while running. 


My next step is to check for gasses in coolant with a test kit, I guess.


Now my one issue is the heater blower is jacked and doesn't run. It started smoking a bit last time it ran so I pulled the fuse on it.


Do you think there's just a massive air bubble causing the over heat bc I'm not properly filling the system with blower on hot to agitate the bubbles out??


I guess it could be timing...I'm not a pro at knowing if that is the cause. The only thing I messed with lately was idle speed screw to get the car to a stable idle after csv backed off.

 Help...trying to get to cars and coffee tomorrow morning :(

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The cooler lower hose indicates your radiator is shedding heat.



You need a way to check to make sure the car is actually overheating.

I use one of those goofy infrared thermometers- aimed at black hoses,

they tend to be accurate enough.  The stock gauge can lose ground, and 

viola, you're instantly overheating.   It claims.


The heater will not make your car overheat.  Bypassing it just might, if your

cooling system is really marginal.  Plugging it would rule that out,

but it just doesn't flow enough water either way to make a big difference.


I agree, tonight, boil your thermostat.  It should be wide open before you get

to a rolling boil.   If you're filling the radiator with the nose up, that should be good.


And get a timing light.  Then you'll know!





Edited by TobyB
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Bad thermostat ..... blocked radiator to some degree ....... blocked flow path somewhere in the head making a hot spot ...... blocked outlet from the head, maybe there is a chunk of something in the outlet pipe from the head (I had that happen once).


Whenever I fill the radiator on my '74tii I pour coolant to the tip top of the radiator, it then flows "backward" through the upper radiator hose and back into the head, to fill the head.  Just for fun I will squeeze the radiator hose on the top of the thermostat just because I think it helps to rid the system of air ..... maybe, maybe not.

    I then leave off the radiator cap and run the engine till it is up to temp.  I can look into the radiator and see (and feel) the hot coolant flowing into the top of the radiator.  Also, I've never had an air bubble problem, and have never "burped" the system. 


Heater motor does nothing to agitate the coolant flow, zero effect.  You simply open the heater valve to "full open" and the coolant then circulates on through the heater and back to the radiator.








Edited by OriginalOwner
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Thanks for the tips...


I'll pull off the new tstat and test it- it's acting like the old one with the cool lower hose.


I assume if the heater box hoses are warm they're flowing and not impeding fluid flow. Or if it's blocked ...it's acting like a bypass.


Ray- I wish it was shenanigans that led to this then I'd know. But I've been sorting a front end shutter and only drove to assess it and to fix the idle speed. 


Only other fix I've made was a new alternator and new battery bc voltage was no bueno- battery was culprit, I have a spare alternator now :)


I think I need to pressure test coolant system and check for exhaust gasses.


Hate to do all this if the car has a trapped bubble somewhere...

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since the old and new tstat work the same, seems less likely that's going to be the problem.  subject to confirming the temp gauge is correct, the radiator is pretty high on my list as the culprit.  you haven't said how old is old nor the maintenance history of it but age and unknown/neglected history raises the probability of the radiator being the issue.

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Update: Drove it a bit today...(went to cars and coffee). Temp was high but stayed i tick just below red.


I went to check fluid levels after the drive and found the notorious frothing in the coolant...ugh. This was worsened by more revs...so I think i've got a blown gasket that may have just come on very slightly and is now more pronounced. Sigh...

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Been there.


Only thing I have to add is draining the block. Plug under #4 exhaust port.   If for no other reason than to learn the history of the cooling system.  If major crud comes out or the flow is blocked, you will learn a lot, and may even fix your problem.


Personally, I lean toward a dead radiator.  The lower portion is heavily corroded inside and impeding flow.

I had mine re-cored with larger fins and 25% more fins per inch = 25% more volume.  Engine temp now stays just below 3 oclock all the time.

Edited by PaulTWinterton
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And of course before you settle on a blown head gasket, do a compression check on all four cylinders.  


I had a slow leak that drove me nuts for several months--I'd lose about a quart of coolant every couple of weeks--not dripping on the ground, water pump OK as was the thermostat, no oil in the water or water in the oil etc.  Did numerous compression tests and all was normal.  Finally on the umpteenth compression test while the engine was cold and had been sitting overnight, I discovered a drop of coolant on a spark plug.  Pulled the head and discovered that the water passage over #1 exhaust port had eroded to the combustion chamber, thus sucking water into the cylinder at each exhaust stroke.  And two of the three remaining cylinders were about to do the same thing.  Head gasket was unbroken and the hole was so small it didn't affect compression.  Local machine shop welded up the head and all was well.  That was 25 years and 80k miles ago.  


Hope that isn't your problem...


I'd have my radiator checked--especially if it's original and has never been cleaned, and while it's out, flush the block.



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