Hi there, I am stumped!

I recently had to replace the thermostat and radiator in my truck (before I replaced it the engine never over heated for an extended period, it didn't even redline fully at any point). That whole fix went off without a hitch and the truck worked perfectly for almost 2 weeks. And then... I drove about 6 minutes down the road to the store and came out to a puddle of coolant under the pickup. I hopped in and made it home without the engine getting to terribly hot. As soon as I got home, again another pool of coolant. I immediately did some looking around and could not identify the source of the leak however I can tell it is on the passenger side under the air filter and carburator somewhere.

Any ideas??

Thank you!

 

Yep. See below, and don't drive until you find and fix the leak.

There are three small coolant bypass hoses, two are on the passenger side under the intake manifold, just where you describe the leak. The other is U-shaped and on the front of the engine near the thermostat. So check/replace those (I got mine from the dealer, but part numbers below are good):

8mm i.d. by-pass hose to – underside of Intake Manifold to Pipe on passenger side: Mazda FE87-13-116 $6, or S-shaped Gates 18100 (cut to length, special order O’Reillys), S-shaped Gates 18100 or Gates 28408

10mm i.d. by-pass hose parallel to cylinder head almost-straight hose going toward the /firewall
Mazda FE1H-15-288 $6 or Gates 28409

10mm U-shaped Bypass hose Mazda FE65-15-284B Gates 18206 Dayco 71348

Also check the two heater hoses:
Dayco 87713 and 87712 special order AutoZone ($7 and $29) or Gates 18900 and 18899
special order O’Reillys

Also on these trucks, tricky to bleed ALL the air out of the cooling system after any coolant-related repair (like your thermostat); I jack up the front end, run engine with radiator cap off for 20 minutes, topping off with 50/50 until it stays full.

 

Thank you for the info! I will dig into that, sounds like that could be it

 

When I rebuilt my B2200 engine in 2011 (smoke) at 183K, I replaced the factory bypass hoses - even though they looked fine for their age/life - with new ones from the dealer, was just so much easier to access the two underneath ones and to do it right, and these were not expensive. Most likely the little metal connecting tube/tee is OK. The factory hose clamps on these I hate, so I replaced them with made-in-USA hose clamps that can be loosened/tightened with a screwdriver or 1/4-inch nutdriver or socket, facing a direction which I could access later if need be. There are photos in my engine rebuild thread MazdaBScene.com - Mazda Truck Owners and Enthusiasts

The front hose is easy to replace anytime.

Also check the two hoses to/from the heater box/firewall.

 

Thanks again for your advice. I ordered the parts and then while I was waiting for them I decided to look a little deeper. I ended up identifying the problem hose and was able to pull it without taking any of the engine apart. It was the longer one right in the middle of your attached image. It was a pain to get out of there but managed to get it and I replaced it with a chunk of fuel line hose from the auto store. Works great now!

 

Great job !!!


That's why I replaced my bypass hoses while I had it apart even though they looked great after 23 years: their age (and my age) and and accessibility.


Yipes !!! Not so good. Fuel line is a different type of rubber, designed to be resistant to gasoline, not hot coolant and water. You need a coolant type hose for longest service life because coolant hoses use a different rubber compound more resistant to hot coolant. From what I read, you better keep an eye on such fuel line used for this purpose (especially if it was fuel line for non-EFI systems) as those are not designed for high pressures; and fuel line will get hard and brittle after a few years with this.

So I recommend getting the right type of hose for this, and swapping that in. Now that you're experienced it should go a lot quicker.