Cant find coolant leak

I was pulling my boat back from the shop yesterday and the truck was running fine. I brought the boat home and parked it, everything seemed fine. I come back out side a few minutes later and the truck is leaking coolant quite fast. All the hoses look good. The water is pouring from the bottom of the crank pulley, behind it or above it. Is this just a bad seal or possibly a more serious problem? I just got the boat and the trailer working and now this!

It sounds to me like your water pump has to be replaced. I would suggest that you have the truck towed to your mechanic for diagnosis.

There is no way for me to diagnose it myself?

If you feel that you are a qualified mechanic, then definitely go ahead. I just assumed that you were not familiar with things mechanical, and it appears that I may have been wrong. Anyway, don’t drive it until this has been repaired.

Can’t find Make, model & year…always helps when asking questions.

Common problem would be the water pump. Easy diagnosis. Fill radiator full of water. If water begins to leak, see where it is coming from. If not, start the truck, and look under truck as it idles, and see where the water is coming. If it is a bad hose or coming from the pump, it should be easy to spot.

Without knowing the make or engine I’ll guess the water pump, on the bottom of most pumps there is a “weep hole” to check if that’s the problem, fill the radiator, start the vehicle and look up from under the at the water pump, may be hard to see OH and wear safety glasses! If thats the problem you’ll see dripping from the pump>

Its a 1977 Chevy C-10. 250 ci. with a th350 auto trans. The radiator is still half full of water. I also could not see where the water was coming from, just the bottom front of the motor. It didn’t start leaking until several minutes after I stopped. The truck was running a little warmer than usual(right after towing a boat), but it was still under half on the gauge.

The motor is a 79’

This leak might only happen when the cooling system is at its maximum pressure of 15 psi. When an engine is shut down, the engine block is very hot, and the coolant is NOT circulating through the radiator. The coolant, then, absorbs that heat and goes to a pressure which is higher than if the engine were running. It may, then, leak at that higher pressure.

I have found a pump-type coolant system tester, with pressure gauge, to be extremely helpful in finding coolant leaks. An auto parts store may lend/rent you one; or, you can buy one. The $75 to &130 for a tester might sound high, but, NOT making one unnecessary part change could easily surpass that cost.

I just tried refilling the radiator with water, it leaks right out without the truck even running. It stops leaking at about half full. The leak is coming from in between the crank pulley and the block.

Is the water pump anywhere near the crank pulley? If not, another possibility is that a freeze plug has let go.

The rad stops leaking at the half-way mark. Check that level point on the engine. Just above the crank? Likely is the water pump, behind the timing cover?

It’s most likely the water pump expelling water through the weep hole located at the front/bottom of the water pump behind the water pump’s pulley. Your water pump bearings are shot and causes undue side-to-side slop on the bad bearings, screwing up the water pump seals and leaking out through the weep hole. Sounds like a standard, run of the mill L-6 250. (“L” stands for “in-line” 6 cylinder). After loosening the V belt by usually loosening the bolts on the alternator to get the belt off, carefully loosen and remove the 4 long bolts that secure the fan to the front of the water pump. Then you’ll be able to get under the front of the vehicle and look for signs of a good leak at the weep hole. If it’s an obvious weep hole leak, remove the water pump and install a new or rebuilt water pump. Check the V belt. If it’s a little rough-looking, buy a new belt, too. Bring the old belt into the parts store so you can do a “show and tell” with the counter person. Most belts have belt numbers printed on them but old belts sometimes are so cruddy that you can’t read the numbers. You don’t say how many miles on the existing water pump but it just might be the original pump. Any signs of leakage at the weep hole requires a new pump. Just be careful that when you take bolts out, remove the fan, etc., that you don’t go ‘godzilla’ on pulling those bolts/fan. Ensure that you don’t put a hole in your radiator. You may also have to remove the radiator cowl to be able to get your hands and tools in there. But you’ll learn pretty quickly. When you replace the pump, if necessary, be sure to clean REALLY WELL the block surface where the pump is. The water pump gaskets are pretty thin and work really well if the contacting surfaces are clean.