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Hey fellas, long time wrench turner here. Picked up a 64 Custom (58k original miles) from grandson of original owner. Car sat covered since ‘92. Installed new battery, water pump, pertronix ign, new fuel tank, Gottafish rebuilt 4100 (fairlane), swapped the 2bbl intake for a 64 date code 4bbl, installed Leed power disc setup and new tires and rims. Been driving mostly summer time for over a year. But 289 NEVER heats up , temp wise. Lower hose is at 90 Deg, no bubbles in radiator, upper will be 125 ish with heater core hoses same. This is after a 40 min drive or a long warmup. Got me stumped. 195 deg t-stat installed but my laser temp reader isn’t picking anything up close to that. What am I overlooking?
 

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Off the top of my head....

Defective T-Stat opening too soon, and/or too much bypass flow around/past the T-Stat.

I know the 289 did not use a flow restriction in the bypass hose, and this may not be related to your issue....
... but a friend had a 79 VW Rabbit that just would not heat up.
Turned out he had replaced all the old and rotting hoses,
but he had overlooked the fact that the factory hoses had a flow restriction hidden inside the bypass hose.
Easy to overlook as the restrictor was just a metal disc with a hole punched in it and jammed inside the hose.
The new aftermarket hoses did not have the restrictor.
Once we figured it out, voila! Heat for the winter.
 

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Discussion Starter #3
Restrictor makes more sense. Thermostat is new and tested at 195 but block seems to not heat up as indicated by the 70 degree lower hose. Since engine isn’t reaching full hot temp, heater core isn’t putting out but input and output are close (not blocked)
 

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Maybe try a restrictor in one of the heater hoses.
The heater core does act as a "bypass", and is basically a mini radiator that has flow all the time,
unless you have a temp control valve on a heater hose. (sounds like you don't?)
 

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Do you see water circulating with the cap off? Did you try a second thermostat? Did someone drill a big hole in the thermostat? 125 degree water coming out of the engine (top hose) says that it's either stuck open or has been drilled. Shouldn't be any flow until the thing opens
 

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Discussion Starter #7
The thermostat is a 195 degree NEW and tested Tstat. Water pump is new (recent) that I installed last summer. It’s odd that the LOWER stays around 70degrees. I’m wondering with that HUGE grill and non clutch fan that it’s getting TOO much airflow. Still scratching my head.....
 

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Well the lower hose is OUT from the rad back to the engine, so the temp you see on the lower hose is AFTER the coolant has been cooled by the rad.

I would still try a different (new) T-stat, no matter that the one you have tested ok.
It's the obvious culprit... and I have seen many new ones test ok and still not work properly.
It is possible yours got stuck/jammed open after it was installed.
At least pull it out and have a look.
 

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Btw, you don't possibly have a "Fail Safe" thermostat, do you?

Cuz if you test it in boiling water it can lock open in the fail safe position...

Copy paste from the intergoogle...

Fail-Safe thermostats are designed with a unique extra stroke that allows operation in two stages:

Stage 1: Within normal operating temperatures, the Fail-Safe operates the same as any other thermostat.

Stage 2: When overheating is caused by a deteriorating cooling system part, the Fail-Safe has a secondary stroke that activates a precision engineered piston that automatically locks the valve into a wide open position allowing coolant to circulate freely.

Note: Once the Fail-Safe thermostat has locked in the open position, it must be replaced and cannot be used again.
 

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I agree with Galaxiex, try a second thermostat, new doesn't always equal good.

You could run the radiator hoses into the ocean, and if the thermostat worked, the water in the block would heat up before it opened. If your water is flowing, the thermostat isn't stopping it
 

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Agree on the "known good" T-stat possibly being bad. The closed coolant system is about as simple of a system as you can get (minus the heater control valve adding some fun to the mix). I recently ran into issues with new and bench tested parts for my 1950 F-1 not working right once they were installed. Drove me nuts tracking down other things until I realized the new part was the culprit. I also found that some parts are definitely better than others (brand name vs. cheaper Chinese knock-offs, for example). But the fail-safe thermostat actually seems like the plausible scenario here. I will say my 289 takes a while to heat up in colder weather, but does eventually get there with good heat output.

Btw, how do you like the Leeds disc system? Did you look at other brands?
 
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