My '96 300 is losing coolant, sometimes as much as a gallon a week. I can't seem to find it dripping anywhere, and I don't see evidence of steam in the exhaust. It even leaked out quite a bit simply parked for a week while I was on vacation. Lately it doesn't seem to lose as much (it knows I'm watching). Any ideas before I replace the water pump?

 

might want to have the radiator looked at or pressure tested. I knew my water pump was bad, but noticed too much coolant to be a bad water pump. Turned out the radiator was bad too.

 

Do you have white smoke coming from the exhaust pipe?? One gallon is lost per week??

I had a bad radiator cap that would allow excessive amounts of antifreeze to enter the reservior and cause it to overflow.Occurs when the vehicle was stopped and the engine was hot. But only a limited amount comes out when the vehicle is stopped--because the pressure is decreasing as the engine is cooling. And this also occurs when the engine was running and in heavy city traffic--and most of the loss occurs when the truck is moving and hot.It took me awhile to notice this--because only small amounts are lost when the truck is parked and the engine is cooling down.
If the reservoir is already low--it wouldnt be noticed until the reservoir overflows--when the truck is stopped--and you happen to be looking at it at the time. It takes several minutes after hot shutdown --before the resevoir overflows and the overflow to the ground is a very small amount of the total amount that is lost altogether.

Yeah--get the cooling system pressure tested and let us know what you find.

I looked at dozens of 92-96 F150s--and most of them showed signs of low coolant in the reservoir and radiator--caused by bad radiator caps--I believe.
Because there was no telltale signs of leakage anywhere.

 

I'm on my second coolant leak this year. Check your hoses real good. I've found that they may not leak when the engine is cold, but they can open up a little once everything is heated up and under a little pressure. This includes the heater hoses and the bypass hose. I just found the second leak this afternoon--it's on a heater hose, and I didn't see any leaks running or stopped, but I touched a funny-looking spot on the heater hose and coolant started squirting out. One good way to check hoses is to bend, poke and prod all the hoses when the engine is cold and running, just watch your fingers with that fan.

Jason

 

The reservoir is usually empty a couple days after I fill it, then the radiator level goes down. Maybe the reservoir has a leak? Some of the hoses are new, some are old. I may start w/ replacing the rest of the hoses. There is no steam (white smoke) in the exhaust, and it continues to use water even if parked a long time. There is evidence of water trickling off the lower radiator hose (no water, just a stain), but I can't get it to leak when I look at it. I once had a Toyota that didn't leak a drop til I replaced the fan belt. When I let the tension off the belt, the shaft dropped about 1/4" (bad bearings) and water poured out.

 

What I was trying to say was that the reservoir will be empty and the radiator will be low when there is a defective radiator cap that will not allow enough pressure to build and will not prevent the boiling point of the coolant to be raised enough to prevent the coolant from boiling into the reservoir and filling the reservior to overflowing . And when the engine is turned off--the contracting coolant when cooling--when cause a vacuum in the reservoir and suck all of the coolant out and back into the radiator.The net effect will be low/no coolant in the reservoir and low coolant in the radiator.

A new radiator cap is just several dollars--and easy to replace.And a defective radiator cap doesnt have to leak--to cause this problem.Just the spring has to weaken. I could hear the coolant boiling in my radiator when the engine was turned off and the truck was hot from city traffic.

 

You could be losing your water pump internally, which will interrupt the flow back from the radiator-then the hot water in the engine pushes the coolant instead of the regular flow. I didn't lose as much coolant as you, but....check the Thermostat housing and the waterpump for evidense of coolant that leaked and evaporated before you can see it drip on the driveway. It doesn't take much of a crack to lose the water you're talking about. This just happened to me.

Oh, and if you need a new water pump...My original pump ran 11 years. In all the years I've fixed my trucks, I just got fed up with going cheap on parts and then having to do the job again in less than a year. Horsepuckies on DAT stuff!
I've had good luck with NAPA or dealer-and stopped going to the other guys for pumps, alternators, hydraulics and ignition parts. I'll slip the soap box back under the workbench now. Thanks....