Why won’t radiator take coolant? (1 Viewer)

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grantgsr

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Jun 10, 2021
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louisville, Kentucky
Trying to flush coolant system in my 1988 62. I drained all of the coolant from the bottom of the radiator out of the petcock. However, when I went to fill the radiator, it only except in a few tablespoons through the top and really never did go down. I could not get any more coolant into the radiator. The neck on the radiator where the cap goes on seems to be angled downward a bit from the top of the radiator, but I don’t see that as being the ultimate problem, because the radiator was filled to the top before I drained it. Also, before anyone asks, yes the radiator completely emptied when I opened the petcock. What completely simple and stupid thing am I overlooking? Thanks in advance,

Grant
 
Before mucking around with spilled coolant, get a gallon jug of water and experiment filling.
If the fill neck got bent down too much, the opening would be lower than the entrance to the radiator and water/coolant wouldn’t flow down.
 
i squeeze the upper hose to get air moving around and sometimes that's enough to help, and did you also want to drain from the block? that's a different petcock on the side of the block (it is on a 60).
 
Hi, They are difficult to fill at the top. Get a funnel ,yellow ones at Walmart next to anti freeze, that seat tightly in the top. Poor slow it should fill.
 
Pull the upper radiator hose at the thermostat housing. Loosen the clamp on the radiator and turn the hose so that the open end is facing up. With the radiator cap off, pour coolant into the hose to fill the radiator.

Because you have an angled neck you have an aftermarket radiator, likely a CSF and they can be a little difficult to fill through the neck.
 
Godwin said:
Pull the upper radiator hose at the thermostat housing. Loosen the clamp on the radiator and turn the hose so that the open end is facing up. With the radiator cap off, pour coolant into the hose to fill the radiator.

Because you have an angled neck you have an aftermarket radiator, likely a CSF and they can be a little difficult to fill through the neck.
Click to expand...
I eventually did this, but could not fill it up because water started running out of the thermostat housing before the radiator was full
 
I"m pretty sure there's a block drain as well. IIRC when I back flushed my '88, I made sure that drian was open to get ALL the old coolant out. Just doing the radiator doesn't get it all.
 
This will help you locate the block drain:

1670527684068.png
 
grantgsr said:
Yes, I guess I will try to find that drain as well.
Click to expand...
My engine is out of the truck and the petcock is removed but it lives here in the back of the block under the last freeze plug.

E8D050F8-4308-4E12-9BB7-9FBD824A05EC.jpeg


If I recall it’s a 17mm. Maybe 14mm? You can reach it from beneath the truck. You may have to remove a heat shield if you still have those installed. It’s been a while since I’ve had mine on and I don’t remember if it blocks that drain or not.
 
cps432 said:
My engine is out of the truck and the petcock is removed but it lives here in the back of the block under the last freeze plug.

View attachment 3188543

If I recall it’s a 17mm. Maybe 14mm? You can reach it from beneath the truck. You may have to remove a heat shield if you still have those installed. It’s been a while since I’ve had mine on and I don’t remember if it blocks that drain or not.
Click to expand...
This should definitely help, thanks!
 
When you drained your radiator it filled up with air- Before you can fill it up there has to an exit for that air. I loosen the top radiator hose and slide a flat head screwdriver under the hose at the radiator so the air can escape.. And as others have said, if you have an extended neck, use a funnel with a flexible end. I cut the flexible end down to about 4" and I can shove it past the bend in the filler neck into radiator. And if you seat it right the funnel/fluid will create a air tight seal at the cap. Start refilling , you should see air burping from the radiator hose you loosened, and when you see fluid flowing out smoothly, pull the screwdriver. Fill the funnel about halfway and gently squeeze the top radiator hose and it will force the air out. Make sure your funnel stays about halfway full, if it goes dry air is getting in the system. Keep squeezing the hose at the thermostat housing and by the radiator every 20 seconds or so and eventually you'll have all the air out of the system- All of this is done while the engine is running with the heat and the rear heater on high-
 
OzarkMtnCruiser said:
When you drained your radiator it filled up with air- Before you can fill it up there has to an exit for that air. I loosen the top radiator hose and slide a flat head screwdriver under the hose at the radiator so the air can escape.. And as others have said, if you have an extended neck, use a funnel with a flexible end. I cut the flexible end down to about 4" and I can shove it past the bend in the filler neck into radiator. And if you seat it right the funnel/fluid will create a air tight seal at the cap. Start refilling , you should see air burping from the radiator hose you loosened, and when you see fluid flowing out smoothly, pull the screwdriver. Fill the funnel about halfway and gently squeeze the top radiator hose and it will force the air out. Make sure your funnel stays about halfway full, if it goes dry air is getting in the system. Keep squeezing the hose at the thermostat housing and by the radiator every 20 seconds or so and eventually you'll have all the air out of the system- All of this is done while the engine is running with the heat and the rear heater on high-
Click to expand...
Great info. Thanks!
When I finally got it it fairly filled with flushing fluid/water I ran it and just continually got little air bubbles so I started thinking I had air getting in somewhere. So I got a coolant pressure tester and put it on and over 24 hours it dropped a couple of PSI. I got underneath and saw very small drops coming from the bottom house at the radiator, and some drips from the area below the water pump. I don’t mind replacing the bottom hose, but will I need a new water pump?
 
The water pump impeller is a fiber reinforced plastic wheel. It’s very robust. It just spins to move the coolant. Water pump failures are typically seen as leaks at the shaft. Basically- if it’s not leaking, its ok.
Out of extreme concern, you could replace it, but it’s very likely that when you remove it you’ll see there’s nothing wrong with it.
 
FYI...it is VERY common to have air in the motor (water passages) after a coolant change. This is problem is unrelated to the radiator problem you have. But since you are a new member I just want you to be aware of this. It WILL cause the motor to overheat. Research "burping" the motor. Watch your coolant temps as you warm up the motor. Don't let it reach the red line. You may have to run it a few times, until the air purges itself. Once the air is out, the thermostat will open and then you should see temps quickly correct. You can try squeezing the radiator hose or jacking the front of the truck up. But I find I can do this by simply running it at idle a few times, turning it off before things get too hot. If the t-stat isn't opening, the top radiator hose will be squishy and cold or warm. When it finally opens, the top radiator hose will get really hot and really tight.
 
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