Losing cooling fluid!


New Member
Jun 21, 2004
Ok, I'm having a cooling system problem. After running my 66 w/ 289 on the highway for about 45min to 1 hour I have to refill the radiator almost a gallon! :jaw: It seems to run fine around town and to/from work (about 30 min driving in traffic) Things I've checked so far:
radiator cap
lower hose has wire inside
flushed out radiator
no leaks in the cooling system (doesn't have loss if I pressure it)
flow seems good (can see it moving if I remove cap)
No moisture on oil dipstick

The radiator is a little cruddy, not sure if that could be it. Its a 2 core. I also have NO fan shroud (I know, I need to get one), and a 6 blade flex fan, which is about an inch to an inch 1/4 away from the radiator. When I stopped the car the overflow hose was literally pouring out steam! The engine idles nice, and like I said no overheating at idle (I even put a thermometer in the radiator to check, about 180-190 at idle). I'm planning on getting an accurate temperature gauge as the dash one is a little sketchy. Any help would be appreciated!
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Look in your radiator when it is empty with a flashlight, I bet some of the rows are clogged. Another problem could be the flex fan. Ever Mustang I have seen with a flex fan has had overheating problems. The fan shourd will help, but it really isn't required. For all you people that say that is not true, look at my car. 4 blade fan with no shround, on a .030 motor with about 16 degrees of advancment, and long tubes. My car has never gotten pass 190 degrees....even after long periods of hard driving or when in stop and go traffic on the 100+ degree days.
Thanks for your reply! There was some white junk inside 6stang7, which is why I flushed out the system, but I bet it could still be clogged some. I have heard that flex fans flatten out at higher rpms, making them uneffective at higher speeds, which could possibly explain why I only have this problem on the highway? But could I really loose that much water because of the flex fan?
Hmm...I don't know about that at high speeds...flex fans flatten out at higher rpms because it's not really needed...there should be plenty of air going through your radiator. It's the same on a lot of cars with electric fans, they shut off at higher speeds. Maybe you just need a bigger rad :shrug:
Yeah, I'm considering getting a three core radiator, but just want to cover everything before I do that. If I spend around 200 for a radiator and still have the problem I wouldn't be very happy with that :nonono:
Did this problem occur all at once or did it come on gradually? Reason I ask is if it came on slowly over a period of time from a good running machine to now what you have it's more than likely something beginning to fail such as the radiator. I have seen cases where motors, after having the heads removed, were reassembled with one of the head gaskets installed backwards. This results in symptons such as yours. The motor runs and if lightly loaded doesn't overheat but will overheat on a 45 min hard run. I have the flex fan without a shroud installed on a .030 289 without the slightest hint of any heating problems
Im almost positive that the white stuff you described in your radiator is a symptom from a blown headgasket. Pickup a coolant sniffer (about 20 bucks) and see if anything comes up. It will determine if there are exhaust gasses in your coolant, and if so you've got a blown gasket.

Do you have an overflow tank on the car? If so then empty it out and drive on the highway and when you stop see if it is full and look for signs it has overpflowed also. You just might have a slight leak in a head gasket that only really shows up at higher RPMs. My Shelby did just this to me and it was crazy but it never fully blew and there was never any water in the oil but a new head gasket solved the problem.
Do you mean an exaust fume sniffer 66? I didn't know that a head gasket problem could only show up only at high rpms/higher speeds, thanks for the info guys. If there are fumes coming out of the radiator, is that a definite head gasket problem? I know that I can see some vapors coming out when the radiator cap is off, nothing big, just a little when it warms up....
I had a radiator develop a small leak which was undetectable, but caused the overflow tank to overflow thus causing the engine to overheat. I guess the pinhole leak was spraying coolant on a hot surface causing it to evaporate quickly. It only showed up after I shut down the engine and noticed a puddle of coolant on the seams of the bottom tank. Just a thought.
OK, I am confused. Are you overheating or just losing coolant? Most of the replies above address overheating, but if your problem is losing a gallon of coolant, your fan and shroud and radiator condition have nothing to do with it.

If your are a gallon low, you will probably not be losing coolant through the overflow. I am suspecting a head gasket problem.

I had a 93 plymouth that blew a head gasket and I was burning 3 gallons per tank of gas. Evfen at that rate, no coolant in the oil and no smoke out the exhaust.
I am starting to think it is a head gasket problem also, because it seems to stay cool on the highway, then when I pulled off to idle it overheated probably because so much coolant was lost.
you just need a new radiator. the one you have is clogged. my 65 FB had this problem, I could drive it for 10 minutes (just enough to reach near full temperature) and come home, let it cool off enough to pop the cap and voila, 3/4 empty. I replaced everything else, pump was new, hoses were new, t-stat was new, rad cap was new. Put a new rad in an ta-da, no more spewing out the overflo hose. Which was a good thing cause before I knew I had this problem really, I drove it for 100 miles and when I got home no fluid. Luckily it was at night so it was cool enough and being as I didnt make any stops basically, my stang ran air cooled. btw, increased rpm such as on the highway causes increased water pump rotation and thus greater pressure inside your rad, with increased pressure the water may not be escaping past the overflo since the rad cap is sensative to pressure. I know I could run mine 10 miles and loose 3/4 the water and other times I could just run it hard for 30 miles and Id loose maybe a cup of water.

You can get a tester for this at a good auto parts store. It is called a "block tester" and I have one. It is a special tube that goes over the radiator fill spout and you put blue fluid in it and then with a special rubber bulb you draw air NOT FLUID from the radiator and bubble it through the blue fluid....if it changes color to green or yellow you have exhaust gases in the coolent.

Jason....I don't think he has a radiator problem, the symptoms are classic mildly blown head gasket.