[cboy]

I'm experiencing something strange with the water circulation on the roadster. This is a 351 Ford with the radiator mounted in the trunk.

I fill the system with water, raising the rear (radiator) end of the car so the filler neck is about 6" higher than the next highest point in the system and allow any air bubbles to burp themselves out and then top off again until I get no more bubbles and the water level stabilizes.

I then start the engine. As the temp gauge begins to rise (usually between 100 and 140) coolant will start flowing out the overflow pipe in fairly large quantities.

My first thought was a stuck thermostat so I pulled it and tested it and it did not open in boiling water. So now I've temporarily removed the t-stat altogether. But when I tested again, the same thing happened, coolant gets pushed out the overflow at a pretty good rate. I also back flushed the system which DID result in a lot of ugly crap coming out the radiator but it didn't solve the problem.

Also, the top radiator hose is warm/hot to the touch while the bottom radiator hose is still cool. The water getting pushed out the overflow is cool/cold and the radiator is cool/cold. The block is hot but the temp gauge only reads between 100-140 when this happens. This happened a bit last summer when I was driving the car a bit but over the winter I had things pretty well dismantled and now the problem seems much worse.

My next suspect on the list is the water pump but I'm getting none of the normal broken water pump symptoms (like squirting out the weep hole or wobble in the bearings etc.) I'll pull it tomorrow to take a look at the rotors but I can't quite imagine this thing isn't pumping. Any other suggestions?

[poncho62]

I'm thinking air in the system............Try 1/2 filling it with coolant, start it up and add the rest slowly as the car warms up.....That should get all the air out. That's how I do it.....

[cboy]

Originally Posted by poncho62

I'm thinking air in the system............Try 1/2 filling it with coolant, start it up and add the rest slowly as the car warms up.....That should get all the air out. That's how I do it.....

The difference being that I have been filling the system pretty well full BEFORE I start the engine/pump - thus trapping air pockets in the system that can't be purged when the pump starts running?

I'm not sure I understand the theory of how the air pockets would be prevented by starting with a half full system and then starting the engine/pump but I'll sure give it a try in the morning...sounds a lot easier than pulling the water pump for an inspection. The one thing that makes me believe you are on the right track is the fact that the system worked fairly well (although not perfect) last summer...no over heating or excessive puking of the coolant.

[56Maynard]

Is the cap any good?

[techinspector1]

"As the temp gauge begins to rise (usually between 100 and 140) coolant will start flowing out the overflow pipe in fairly large quantities."

Maybe there's something I'm missing here. How is the water getting past the radiator cap? The system can't possibly be up to pressure at 100-140. Try a new cap? 16-17lbs?

[56Maynard]

Yeah, thats the only thing I can think of....Maybe the rubber seal and or the spring is junk. Most people don't realize that a cap should be replaced every few years when you change and flush the system. At any rate, if 140* water is gettin past the cap, something is wrong.

[xntrik]

Originally Posted by techinspector1

"As the temp gauge begins to rise (usually between 100 and 140) coolant will start flowing out the overflow pipe in fairly large quantities."

Maybe there's something I'm missing here. How is the water getting past the radiator cap? The system can't possibly be up to pressure at 100-140. Try a new cap? 16-17lbs?

I agree,

#1) thing to check and replace if not holding pressure. Also check that new cap with a pressure tester. 90% of caps are 2-3 pounds lower than their rated pressure.

# 2) The lower radiator hose going back to the engine is probably sucking flat because it has no "spring" in it to prevent collapsing, so the water pump is making enough "circulation pressure" to force the coolant out of the cap.

A plugged radiator will give the same overflowing effect.

Grab a coat hangar wire and wrap it around a broom handle to make "hose springs". Be sure to do a little loop in the ends of the wire so that it will not make a hole in the rubber hose.

If you have a long run of hose, use exhaust pipe tubing appropriately bent as the water "hose" connecting each end with rubber. Allow enough rubber to flex and prevent stress on the radiator, etc.

You said the coolant is "warm" so it is not likely that your gauge is reading incorrectly.

[Triaged]

I think there is 1 thing you are missing.

Water expands when it gets warm. As the water expands it will go past the cap and out the overflow (hopefully into a res.). When the engine cools back down (and the water shrinks) it will get sucked back into the rad. (as long as the end of the hose is below the water level in the overflow res.

This is why all cars say "CHECK HOT" on the side of the tank.

[GoneNova/406]

drill 3, 3/16's-5/16's holes in your thermostat and it'll cure your air problem and not affect anything else in a bad way.did you add an electric inline water pump to the system along with your belt driven pump?doesn't seem like enough water pres. for that distance to travle.meziere has a 20 gpm pump at jegs for about 175.00,then you would have a pump at each end of the car.

[IanRiordan]

351 huh, Windsor or Cleveland?. I assume Windsor as we hung onto Clevelands much longer.
If the cap is ok and it is suited to the radiator/recovery system you have, could you have a reverse rotation pump on a clockwise system or vice-versa? Also 'top hose hot, bottom cold'. I hope this is a crossflow 'cause if it's a vertical flow it sounds bassarkwards - you know heat rises etc. good luck.

[cboy]

Thanks for the brain storming guys. Gives me a number of ideas to try out this morning.

Definitely could be a bad cap...as the radiator core is brand new but the cap is the original. So I'll try the cap from my pickup which I know is good.

Also, problem could be compounded by an air pocket - so I'll fill the system according to Poncho's directions.

I don't think it's "flat" hoses...since the lower has a spring I've been observing the hoses throughout, and they are not contracting.

Also, the flow is not now being held up by the thermostat - because I removed the guts of the t-stat completely.

I don't believe it's a plugged radiator - it's brand new (yes, it is cross flow). Also, I've back flushed the system until the water runs perfectly clear.

One item I would highlight, however, is the extreme difference in temperatures when this occurs. I can run the engine up to operating temp. (190) and the radiator will will remain cool to the touch. This will push rather large amounts of coolant out the overflow but the exiting coolant will be at ambient temp (cool to the touch) while the block temp is very hot.

One final "theory" question. If the radiator cap is bad, could that result in a failure of the coolant to circulate throught the system (i.e. the system never comes up to pressure because everything is being pumped out the cap rather than around the system)? I would still think I ought to be getting hot water pumped out my overflow...but that is not the case.

Hopefully I'll have a bit more to report in a couple hours. Keep the ideas coming if you have them.

[farna]

Could be that your radiator is that efficient. Hot water goes into the side opposite the cap (the cool side). I'd replace the cap and use a recovery tank setup instead of a plain overflow. Your system holds a good bit more coolant than a stypical cooling system because of the long runs of pipe/hose, which also help it cool better. The water going into your radiator has to be a bit cooler than a typical engine setup after that long run of pipe. You likely get a bit more expansion than normal, and have more radiator than needed. The higher volume (mass) of water will cool better than a lower volume would, indicating a smaller than normal radiator would have been fine.

[cboy]

And the winner is..........bad radiator cap. I replaced the old one with a working cap from my pickup and the problem was instantly solved. Just went out for a short "cruise" and the cooling system was flawless. (BTW - it's a GREAT day up here in Wisconsin for riding around in roadster.)

Thanks to all for your input. As usual, I learned something new.

Dewey