How do I track down a coolant leak?

[Drew Bru]

Just had the water pump replaced after a catastrophic bearing failure. Now, while idling, I see some drops of coolant scattered beneath the bus. This could be residual leftover slop from the water pump failure but I'm wondering if there's a pinhole leak somewhere or a leaking hose or something. With the fan running it can be hard to track it down though.
I've washed the engine bay pretty good and tomorrow I'm planning on putting a big sheet of cardboard under the engine and idling it for an hour or so. I figured the system should be pressurized when I shut off the engine (and the fan stops) and any pinholes may be weeping...but that may or may not be how any of this works.
Any tips or tricks I should know about? How does one go about tracking down a coolant leak?

 

[BarnYardCamp]

if you have a Auto Zone store near you..
you can borrow a pressure tester...you pay for it, then get your money back when you return it. (yes, that's how it really works)
put the thing on the radiator cap and pump it up to the pressure stamped on the cap.(6 -10#?)
then you can look for the leak with out having to risk life and limb around the running engine, and with out having the cooling fan blow the drips around sending you on a wild goose chase.

 

[Veloc]

With the coolant leak you described, I think your first step should be to wash the engine bay. Coolant will go everywhere, sticks kinda like oil, and will take weeks to cook off/evaporate out. Be mindful of the engine's air openings, oil cap and the like, you don't want to pressure wash those areas.

 

[Drew Bru]

With the coolant leak you described, I think your first step should be to wash the engine bay. Coolant will go everywhere, sticks kinda like oil, and will take weeks to cook off/evaporate out. Be mindful of the engine's air openings, oil cap and the like, you don't want to pressure wash those areas.

Thanks. I did pressure wash as you described and I let it dry overnight. I'll take a look at it today and see just how clean it came. I figured carefully pressure washing it was a good place to start, as that stuff was just everywhere and there's no telling if the drips were new or from the initial water pump failure.

 

[Drew Bru]

if you have a Auto Zone store near you..
you can borrow a pressure tester...you pay for it, then get your money back when you return it. (yes, that's how it really works)
put the thing on the radiator cap and pump it up to the pressure stamped on the cap.(6 -10#?)
then you can look for the leak with out having to risk life and limb around the running engine, and with out having the cooling fan blow the drips around sending you on a wild goose chase.

I do have an Autozone nearby, and that's a really great idea. I think the only radiator cap is on the reservoir though. Its not a standard radiator cap like a car, its threaded. Haven't looked for a pressure rating but I don't remember seeing one. Maybe they have an adapter though?

 

[BarnYardCamp]

Maybe there is some sort of adaptor. If you are able to use the pressure test, don't get too aggressive, just a few pounds of pressure should do it.
If the leak isn't exposed, then maybe try it again with the engine at full op temp. I've seen (in cars) where the thermostat housing had a hair line crack that only leaked when everything was hot.

 

[cadillackid]

I dont know how your DT is set up but mine was set up where the reservoire is pressureized.. the cap on it is a pressure cap.. then there is a little bleed hose that comes off the cap-nectk and just routes to the ground.. no recovery like a car.. if you fill the reservoire to the top then when the coolant expands it will reach the 10 PSI of the cap and send some down to the ground..


if the next time you drive it, the engine gets a little hotter then coolant will expans a little more and it will send a little more to the ground..



often the expansion release will occur right after you shut the engine off.. as the coolant within the engine actually gets hotter for a short time after you shut down..


on mine I have a "recovery bottle".. literally a 2 litre diet coke bottle where the coolant goes when it over expands and gets sucked back in when the engine is dead cold..



definitely a good idea to look for any leaks you can find though too...