# Help me find a small coolant leak **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** mazda3, mazda\ **Created:** [December 21, 2024, 11:48pm UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476 "2024-12-21T23:48:01Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![oldnotdeadyet](https://avatars.discourse-cdn.com/v4/letter/o/a6a055/32.png) [@oldnotdeadyet](https://community.cartalk.com/u/oldnotdeadyet)\ **Post date:** [December 21, 2024, 11:48pm UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/1 "2024-12-21T23:48:01Z")
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! ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [December 21, 2024, 11:56pm UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/2 "2024-12-21T23:56:08Z")
We use a cooling system tester that pressurizes the cooling system exposing leaks. ![image](https://global.discourse-cdn.com/cartalk/original/3X/f/b/fb703c33fbfe51d2468a8873900e07972f1578c2.jpeg) Tester ---
**Author:** ![oldnotdeadyet](https://avatars.discourse-cdn.com/v4/letter/o/a6a055/32.png) [@oldnotdeadyet](https://community.cartalk.com/u/oldnotdeadyet)\ **Post date:** [December 22, 2024, 12:01am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/3 "2024-12-22T00:01:40Z")
Is that typically successful on both cold and hot engines? ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [December 22, 2024, 12:16am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/4 "2024-12-22T00:16:13Z")
If the engine is hot, the cooling system is already under pressure. Tester ---
**Author:** ![oldnotdeadyet](https://avatars.discourse-cdn.com/v4/letter/o/a6a055/32.png) [@oldnotdeadyet](https://community.cartalk.com/u/oldnotdeadyet)\ **Post date:** [December 22, 2024, 12:30am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/5 "2024-12-22T00:30:48Z")
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. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [December 22, 2024, 12:41am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/6 "2024-12-22T00:41:13Z")
> [@oldnotdeadyet](#): > > 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 ---
**Author:** ![oldnotdeadyet](https://avatars.discourse-cdn.com/v4/letter/o/a6a055/32.png) [@oldnotdeadyet](https://community.cartalk.com/u/oldnotdeadyet)\ **Post date:** [December 22, 2024, 12:46am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/7 "2024-12-22T00:46:33Z")
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. ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [December 22, 2024, 1:36am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/8 "2024-12-22T01:36:15Z")
> [@oldnotdeadyet](#): > > It sounds like the coolant system should have a Schrader valve 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. ---
**Author:** ![oldnotdeadyet](https://avatars.discourse-cdn.com/v4/letter/o/a6a055/32.png) [@oldnotdeadyet](https://community.cartalk.com/u/oldnotdeadyet)\ **Post date:** [December 22, 2024, 1:47am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/9 "2024-12-22T01:47:16Z")
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. ---
**Author:** ![oldnotdeadyet](https://avatars.discourse-cdn.com/v4/letter/o/a6a055/32.png) [@oldnotdeadyet](https://community.cartalk.com/u/oldnotdeadyet)\ **Post date:** [December 22, 2024, 1:51am UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/10 "2024-12-22T01:51:49Z")
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. ---
**Author:** ![weekend-warrior](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/weekend-warrior/32/26122_2.png) [@weekend-warrior](https://community.cartalk.com/u/weekend-warrior)\ **Post date:** [December 22, 2024, 9:13pm UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/11 "2024-12-22T21:13:21Z")
[3220.fm](https://static.nhtsa.gov/odi/tsbs/2016/SB-10092584-6903.pdf) ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [December 22, 2024, 10:08pm UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/12 "2024-12-22T22:08:42Z")
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. ---
**Author:** ![oldnotdeadyet](https://avatars.discourse-cdn.com/v4/letter/o/a6a055/32.png) [@oldnotdeadyet](https://community.cartalk.com/u/oldnotdeadyet)\ **Post date:** [March 29, 2025, 12:20pm UTC](https://community.cartalk.com/t/help-me-find-a-small-coolant-leak/198476/13 "2025-03-29T12:20:45Z")
I finally rented a pressure tester made by PowerBuilt. Advance Auto has you pay full purchase price ($300 !!) and then you can return it. None of the screw-on caps fit, but the device also has small, medium and large tapered plugs with an interesting enlargement method. In my case, the leak was so small that it either wasn’t leaking when warm, or it was immediately evaporating. Apparently, when cold, the pressure was so low that it didn’t leak. So the small drops must have come at mid-temp. Bottom line: the pressure tester caused an easy-to-find leak at the thermostat mount. (I haven’t dug into the replacement project yet. We can award Tester 10 points for being the first to suggest this method.