I have a 2007 Mazda 3 with 203K miles. I noticed a small puddle of coolant under the car after parking on a modest down slope. The coolant level was well below the MIN level. Removing the engine undercover showed that it had collected a small puddle also. I added a quart of coolant and drove without the undercover, and the dripping seemed to stop, possibly because the increased air flow may have carried the coolant constantly, before it puddled. Re-installing the cover re=started the puddling. Of course, I am watching it (and the temp gauge and engine performance) closely. 200 miles of driving caused the coolant level to fall a little less than a quart. I seem to recall that dyes are sometimes used to locate small leaks. What does an experienced mechanic do? (I do not hear any bearing problems with the water pump, but I don’t think I can see the weep hole. And, I see no residue on the hoses. Help!
Is that typically successful on both cold and hot engines?
If the engine is hot, the cooling system is already under pressure.
Tester
True, and the pressure is probably limited to that value via the radiator cap (or coolant tank cap, in my case.) The cap bleeds off excess pressure.
Maybe I can rent this tool.
Some parts stores rent this tool. But beware. The ones they rent don’t always come with the proper adaptors to connect the tool to the cooling system.
Tester
It sounds like the coolant system should have a Schrader valve, and then all I would need would be a bicycle pump wity a gauge.
There’s a lot I haven’t seen, but I’ve never seen a coolant system with a Schrader valve. You might be thinking of fuel. Those pressure testers screw onto the radiator cap (or pressurized tank in your case).
Have you tried just running the car while up to temp and looking around at likely leak areas. If you can see where it’s puddling you can usually work your way up to a leak location.
Yes, I tried. Of course, step 1 was to remove the underdover. By the time that was done, it appears that any leaks had evaporated . I was all around that area with the engine stopped and running. Lying on my back under a running car on ramps is a little nervous-making. I also drove the car for a few days without the undercover, and could not find drops when parked. It seems like the undercover traps the drops, and they are dropped on the ground when the car is parked on the mild hill. But this is after 200 miles of driving.
I like the idea of pressurizing the cold engine.
YouTuners suggest that 170K is a typical life for these water pumps. I might just replace mine to eliminate the variable, and possibly find something else in the process.
I don’t know the best method, but I’ll tell you what did. I’m just a simple-minded diyer. Like you, I couldn’t find the source of a small coolant leak so I replaced the water pump on a flyer. I did this even though there was no obvious leak in engine compartment, nothing from water pump leak hole, no hose leaks I could see, etc… It was time anyway, pump was original to the 200k mile car. It’s a pretty big job on the Corolla, timing belt covers, jacking engine, etc. Only after I got everything removed enough to access the water pump bolts, then I could see the leak. Water pump shaft seal was obviously leaking. New water pump solved the leak.
I think a cooling system pressure test w/UV dye would have worked pretty good too. I didn’t have any of that equipment though, so I just gave the wheel of fortune a whirl, and fortunately got lucky. The Corolla had been removed from the road for several years anyway due to a pandemic/emissions-testing issue.