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I've lost my mind!!

Bryan T

New Member
Joined
Jul 31, 2014
Messages
42
Loc.
Oshkosh
Ok guys looking for help/ advise. I'll start with the problem. My coolant from my radiator keeps filling my overflow tank and not going back into the radiator and cooling. I've recently put a new 302 motor in that was built by my father but machined by an engine shop. Engine block was cleaned and bored I think 30 over. Heads were redone also, new valves, springs, and new valve seats. I'm running the stock radiator (was tested by a radiator shop) stock flex fan with the stock fan shroud. I stuck a new 160 degree thermostat in also.

The motor is not over heating at all, running around 160- 180. Today I decided to do a Combustion Leak test and the liquid turned from the dark blue to a green color. After doing this test and letting it sit for about 3 hours I noticed that my overflow tank is almost empty now. It got sucked back into the radiator. This is that part that blows my mind why it has never done it before and after doing that test it sucks it back in.

I pulled all the plugs last night and they all looked great.

Can someone give me some advice on what I could do next for a test or if anyone has had this issue before.

Thanks in advance,
Bryan
 

Slowleak

Bronco Guru
Joined
Sep 12, 2013
Messages
3,732
Loc.
Georgia
Could be a bad radiator cap. It has a valve in it to allow coolant to return. Make sure your overflow hose goes all the way to the bottom of the overflow tank and that the hose doesn’t have any holes. It could be pulling air back into the radiator instead of coolant. Check the clamp where the overflow hose connects to the radiator too... worse case is that you have a bad intake gasket or head gasket.
 
Last edited:

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
With a recovery system, the cap needs a gasket to seal the top of the radiator neck. Make sure yours is there and in good condition.
 
OP
OP
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Bryan T

New Member
Joined
Jul 31, 2014
Messages
42
Loc.
Oshkosh
With a recovery system, the cap needs a gasket to seal the top of the radiator neck. Make sure yours is there and in good condition.

Yes it has both seals. The radiator cap was brand new. I'm just wondering if anyone has ever had this issue before I go and rib off the heads.
 

SHX669

Bronco Guru
Joined
Jan 9, 2009
Messages
1,997
"almost empty " just how low is that ? Fill the overflow about 1/2 full . If your radiator cap is functioning correctly it might be sucking air back into the system.
You said you waited three hours and the overflow was almost empty - how long of time did you previously wait before checking the fluid level ? It takes a while for things to cool down and start the "recovery " process.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,353
I think a 160 degree thermostat is too low for a Bronco's engine to stay in the happy zone. And for sure you'll be wanting to replace it for the winter in your area!
Even here in CA my heater barely worked with just a 160. And I was trying to fix a non-existent problem anyway. Did not have a heating issue with the engine, I'd just heard that lower t-stats were the thing to do for "performance" but didn't quite get that it was more of a crutch for other things.
Generally the engine runs more efficiently with the 180 to 195 range stats. Unless you were already having an issue with the higher temp versions?

And maybe, pertinent to this discussion, your engine coolant is not heating up enough to let the expansion and recovery system function properly. Just not enough variation in temps, so not as much expansion and contraction as it's designed for.

Second, what kind of overflow/recovery tank is this? Stock from a '73 or later? Or is it aftermarket? If so, what size is it. Too small of a tank can puke out coolant on the ground (defeating the whole purpose of a recovery tank of course) and that's less available to go back to the radiator. And just might keep the tank looking full even though it's functioning.

Is the radiator going empty after at time? Did your combustion gas test indicate any gasses? If so, that's the only reason to even consider removing the heads at this point. You don't pull the engine apart to find out why your radiator cap and recovery tank are not functioning as expected.
If the test did not pinpoint any combustion gasses in the coolant, there is absolutely nothing inside the heads that is going to tell you why your coolant is not pulling back into the tank.

You said it's not overheating, and it's running well and the plugs look good. So what actually has you concerned about the coolant not being pulled back in?
When the recovery tank is full, how low is the level in the radiator? Does the radiator eventually just go empty? If not, then the system may actually be working and might just be over-filled.

I forget the precise level of coolant in the radiator, but it's usually an inch or so below I think. If it fluctuates back and forth, that's normal. If it keeps going down until empty, then yes, it's not doing it's job. But you did not mention that I don't think.

Got pics of how it's set up? Stock radiator and tank?
But either way, even though it's running well and staying cool, I'd replace the thermostat, unless you were having trouble with heat before.
For the long-term health of the engine.

Paul
 

tirewater

Contributor
Sr. Member
Joined
Jan 28, 2011
Messages
1,040
Loc.
San Francisco Bay Area
Today I decided to do a Combustion Leak test and the liquid turned from the dark blue to a green color.

Seems pretty obvious that you'll need to remove the heads if you're getting combustion gases in the coolant.

I would double check with a compression test as well. That way you can determine which side has the problem and perhaps only have to remove one head.

Carefully watch for what's causing the problem as you dissassemble. Improperly torqued head bolts, warped or cracked head, bad head gasket, etc...
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,353
Good point. I meant to ask what all that meant, since I did not know what color meant what in his particular test.

I take it that Green means bad in this case?

Paul
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
With the engine cold loosen the radiator cap and put the front tires on ramps or up on the curb. This will put the nose of the truck up high enough so air wont be trapped in the engine. Now remove the cap completely before it gets too hot. With the engine running pull the heater valve so coolant flows through the heater. Now watch the coolant in the radiator until its hot and circulating. The top radiator should be veru hot too. When hot and circulating fill the radiator to the top and cap it. Fill your recovery tank half full. You can take your truck down and park it. Now your system is full and should work properly.
 
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