Why is my CJ Puking Coolant?

OK, here is what my 79 CJ5 is doing - when I drive it for any amount of time, any distance, in any temperature, as soon as I park it and turn off the engine, it pukes about 1-2 cups worth of coolant out of the overflow tube onto the pavement.

Now, here are the details of my Jeep's current state: the original 304 was just rebuilt and has less than 100 miles on it (all 100 miles have been spread out over the last 5 or 6 months, it's basically just a summertime show car now). The original radiator was reconditioned, pressure tested, given the seal of approval, etc. Everything worked fine and it ran great until just recently. My temp guage wasn't working upon initial start-up and break-in of the engine, so about 20 miles ago I replaced the temp sending unit. Now my temp guage works, but that's about when the problem started. My temp guage reads exactly half way between cold and hot and never strays, even on a really hot day (but I haven't strained the engine at all). So I replaced the radiator cap with a brand-new one, hoping to fix the overflow problem. It's still puking coolant. What is going on? Any ideas would be appreciated. Thanks!

 

Put an overflow bottle on it...

 

Maybe your thermostat is sticking.

 

I agree and also check with another temp gauge. if I'm not mistaken most autozone stores have infared temperature testing. just point and read.
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I know my cj prefers to run with about 1.5-2" of airspace in the radiator (checked when cold). If I filli to the neck, it alwyas pukes the extra into the overflow.

 

What can be happening is if you fill your radiator completely full there is no room for the coolant to expand. When the vehicle is running the heat in the block and heads is disbursed by the coolant, when the vehicle is running the water pump circulates the coolant thru the radiator and keeps the liquid cool. As soon as you turn the vehicle off the liquid stops circulating but there is still lots of heat in the block and heads. At this point the liquid can heat to the boiling point causing the rest of the coolant to expand allowing the coolant to be lost thru the overflow. Confirm your coolant system is working properly then just run the coolant about an inch low or add a coolant recovery tank.

 

Yep, in the days before all cars came with coolant recovery systems, you would normally fill the radiator only to within an inch or so from the bottom of the filler neck. If the radiator vented a little coolant, that was fine, as long as the radiator core was covered when cooled.

I think the coolant recovery bottles became popular because of the popular notion, true or not, that there is something wrong with or suboptimal about the cooling system when coolant comes out. I'm not sure that the coolant recovery system makes that much difference in the cooling capacity of the system, but it does eliminate any puking of the coolant onto the ground. In modern times, this has become more important because coolant runoff from the roads is considered an avoidable environmental pollutant.

 

What confuses me is that the coolant level was set months ago, and this overflow problem didn't start until recently, right after I replaced the temp sending unit. So if the coolant level was initially set too high and the heated-up coolant didn't have room to expand, wouldn't it have been happening from the get-go?

 

Mel,
So when you changed the sending unit, you didn't add any coolant to relplace what leaked out ????

SPW

 

BLACKMGTD,

No, I did it as quickly and carefully as possible and only lost about 1/4 cup or so of coolant when switching out the old sending unit.

 

You may have introduced an air pocket that hasn't filled yet. Try filling the system and letting it self clearance again (with a bucket under the overflow tube).

 

I worked in a FLAPS in the 70's. We sold lots of the coolant recovery kits, The sales pitch at the time was that in addition to keeping the radiator completely full of coolant it kept the system more corrosion free. The reasoning was since each time the coolant expanded and contracted it introduced fresh air into the system. Since oxygen is needed for rust to take place it was thought without air in the system rust could not occur. I think the fact all vehicles are now equipped with the recovery system it is probably more out of environmental concerns than rust or coolant efficiency.

 

Please keep in mind that my experience is with British cars over heating. I do not know if this applies to a Jeep. My guess would be you are either over filling the radiator or the radiator cap is not sealing and the system is not pressurized.