Radiator cap eruption?

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I ran an errand today, about 10 miles, max speed 45 MPH. When I got home, I noticed wetness around the passenger headlight. It was coolant. The "overheat" idiot light never went on. The cooling system has been flushed twice recently, once at 1,900 miles, and again at 2,500 miles. Mileage is now 4,400. The coolant is less than 50% water. I recently replaced the lower radiator hose, which hasn't shown any sign of leakage recently. When it was leaking, I used a radiator cap with no pressure washer, to minimize leakage. Today was my third trip with a pressurized cooling system since fixing that leak. When the engine is hot, the upper radiator hose is hard, and I find no leaks.

In the photos, you can see where the coolant sprayed. The radiator had about 1/2" of air at the top when I opened the cap (after it was cool). I thought I had eliminated all the air, but perhaps not. The overflow tank was down about 1/2" from where I filled it a week ago.

Clearly, I need to top off the radiator and the overflow tank. I don't know how old the radiator cap is. It looks OK, but I can certainly replace it.

Does this indicate a problem in my cooling system? Or is it as simple as a new radiator cap?

Thanks in advance for all advice and wisdom. I'm still a CUCV newbie.

 

[CUCVLOVER]

I think it is just air pressure. Try letting it cool off, then start is and let it run with no cap. That should help it work out the air without forcing coolent out first. Just make sure you have some coolent ready to go in it just in case a lot of air comes out and drops the level really fast.
Also I would change the cap.

Let us know if that helps.

 

[tim292stro]

Coolant getting pushed out usually signifies a pressure introduction in the cooling system. If you smell something that's similar to exhaust from the radiator cap opening with the engine running, you may have a blown head gasket. It goes without saying that you should start with a cool engine for this!!!

Check the radiator cap first - they are supposed to be two way pressure valves (hot expand = coolant to overflow tank, cold contract = coolant back into radiator). They fail after years, no matter how well you treat them. Next thing to check for is an obstruction on the coolant recovery tank hose from the radiator neck - if that is clogged, it won't matter if the radiator cap is working right.

After that you can check your thermostat - if your radiator is belching coolant and you turn on your cab heater and it stops, that tells me the coolant can't get past your thermostat and recirculation plumbing.

All it takes is a big flake of rust blocking a passage and your water pump will squeeze coolant out where-ever it can.

 

[nyvram]

After that you can check your thermostat - if your radiator is belching coolant and you turn on your cab heater and it stops, that tells me the coolant can't get past your thermostat and recirculation plumbing.

yes yes and yes. i've seen a couple youtube videos where the thermostat came apart in pieces in a CUCV when they went to replace it and the one in ours was stuck in the 'open' position. it was in pretty bad shape so if you've never replaced yours, that's a pretty good thing to swap out while you're messing with your radiator.

 

[eme411]

a good trick to get the air out is keep the heater hose on the crossover off and take your time filling the rad, heater controls open , almost all the air will be out of the system them ,wait until coolant comes out of the fitting then reinstall the hose, then let the engine run until the thermostat has opened and the rad is hot on both sides,

 

[the skull]

When I do anything with the cooling system, I use a coolant "burp" funnel
I got from the tool truck guys. It works pretty well, has a lot of different
fittings and gaskets, one for the GM stuff as well. Just let it run with the funnel
in place til the air bubbles stop. On the other hand, if the bubbles never stop
when it's warmed up, you can have compression leaking into the cooling
system somewhere. Hope this helps.

 

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I think it is just air pressure. Try letting it cool off, then start is and let it run with no cap.

I figured I'd try this first, since it's simplest.

I parked on the steepest slope I had handy, nose up, to help any air get to the radiator and out. I did get some air out that way, running the engine and letting it warm up with the cap off. In testing the hose to the overflow tank, I found the tank was empty! I'd been looking through the outside of the translucent tank at a stain on the inside, thinking that was my coolant level. Oops. Overall, I added a gallon of coolant to the radiator and the overflow tank. If that represents the volume of air that burped out, then I had a lot more air in the system than I'd realized.

I had the heater blowing hot air during this, so that plumbing was circulating also.

If I continue to have problems, the cap and thermostat are my next targets.

Thanks for all the help!

 

[Rvitko]

Are you sure you moved over the spring or your new lower had a spring? Without it the lower collapses and you will get an overheat. Inside the lower should be a big slinky like spring.

 

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Are you sure you moved over the spring or your new lower had a spring? Without it the lower collapses and you will get an overheat. Inside the lower should be a big slinky like spring.

Yes, my new hose has the spring. I had to push it further into the hose when installing, to get it out of the way.

 

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if the bubbles never stop
when it's warmed up, you can have compression leaking into the cooling
system somewhere.

My bubbles stopped, fortunately. I ran it until the cab heater was blowing full hot. After the initial burps subsided, I got no steady stream of bubbles as one would expect if exhaust gasses were leaking into the cooling system.

 

[the skull]

My bubbles stopped, fortunately. I ran it until the cab heater was blowing full hot. After the initial burps subsided, I got no steady stream of bubbles as one would expect if exhaust gasses were leaking into the cooling system.

Awesome.
At the honda shop we call those "bubbles of death".
Smells like exhaust, bad times all around.

 

[tim292stro]

When I do anything with the cooling system, I use a coolant "burp" funnel I got from the tool truck guys...

...I parked on the steepest slope I had handy, nose up, to help any air get to the radiator and out....

IIRC (from a TV show I saw 15+ years ago, before How It's Made I think), GM uses a burp funnel equivalent and they pull a vacuum in the coolant system with the overflow hose (which goes into the overflow tank from the radiator neck hose) until the engine reaches temperature at the factory. Vacuum makes the bubbles expand and consolidate, which in turn makes them easier to flush through the system by running the engine/water-pump. The bubbles expand out the overflow plumbing, then they release the vacuum and it back-fills with coolant - do this a couple times over several minutes (vacuum, release, vacuum, release) and soon all of the air is out of the system and they cap off the overflow tank after setting it to the hot-full level.

 

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The plot thickens.

It turns out my lower alternator belt rubbed a hole in my lower radiator hose, again. There's about 1" clearance between them when parked. I guess there's enough movement that they rub together sometimes. I guess that makes sense. The belts move with the engine, and one end of the hose moves with the engine and the other moves with the frame.

So the hole in my suction hose allowed air into the coolant when driving, and leaked coolant when parked, which explains where all that air was coming from, and where the coolant was going.

I tried a generic hose, but I can achieve no better clearance that way, and it kinks near the water pump, between where the spring ends and where the water pump starts.

So now I'm trying to fashion a hose shield. There is one in the TMs, but the part is not available anywhere that I can find.

If I can keep the air out, then perhaps I can prevent the coolant eruptions through the radiator cap.

I also ordered a new cap. The seal on the old one was compressed and hard.

 

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For the record, a new cap solved my eruption problem. A new lower radiator hose with a shield solved my problem of air being sucked into the coolant. I still don't have the *right* lower radiator hose, but I have one that doesn't leak and is shielded from the belt. The cooling system holds pressure now, doesn't leak, doesn't erupt, and I think all the air is eliminated.

So the coolant eruption was the truck's way of telling me about a pinhole leak in the lower radiator hose allowing air into the coolant, and that it was time for a new radiator cap. I'm learning to speak CUCV!

I've ordered a couple of different solutions for the lower radiator hose. If I find one that works well, I'll post. The "generic" hose I'm using now has kinks that make me see it as a temporary fix.