Cars, Computers, & Random Thoughts
Mazda 3 – Thermostat and Water Pump
Mazda 3 – Thermostat and Water Pump

Mazda 3 – Thermostat and Water Pump

Preventative maintenance is an important part of keeping your car reliable. Whether it’s due to a dubious repair history, an upcoming milestone, or you just want something to work on, preventative maintenance is a good way to keep things running and in tip top shape. It was in that spirit that I decided to change out the water pump on my Mazda 3s. It hadn’t been done that I could tell, the part is cheap, and I enjoy working on my cars. For the most part. I also wanted to replace the serpentine belt as I didn’t have any record of that being done either.

I went ahead and picked up a Gates water pump for something like $30 and I also picked up a MotoRad thermostat (would not recommend, lasted only four months) as it’s in the same area, cheap, and it seemed like a good idea to replace it while I had everything else apart. I noticed there was some belt squeal/squeak going on as well so I got a new tensioner pulley to complete the set.

So what does the actual work look like? First, a shot of what I’m working with, Mazda didn’t make this one easy.


As you can see, the serpentine belt looked a bit long in the tooth. There did seem to be a recent-ish air conditioning belt replacement though. That’s unfortunate because you need to remove the a/c belt to replace the serpentine belt. Since it was yet another low cost part, I picked up a new one.
First you’ll want to grab a 14mm wrench and slap it on the tensioner pulley bolt. It’s reverse threaded so you can push it towards the fire wall to loosen the tension on the belt and slip it off. For the a/c belt, as I had elected to replace it, I just cut it off. You can also remove the a/c compressor if you want an easy way to remove the belt if you plan to keep it.
There are only three 10mm or 12mm bolts holding the tensioner assembly on.


Likewise, the water pump pulley is held to the water pump with three bolts. I believe these are 10mm and tricky to get to. A tip to save some time, loosen these bolts while the serpentine belt is in place or you’ll end up spinning the damn thing this way and that trying to loosen the bolts. If you go that route it is a very tight fit so it’s up to you which hell you want to deal with.


The pump itself is held in with more 10mm bolts, 5 in all I believe. Remove 4 and try to pull the pump out, if it doesn’t move then there are definitely 5. These are also pretty tricky to get to, use the new pump as a reference of where the bolts are as you won’t be able to see them all. A pair of gloves will save your hands from all the sharp aluminum edges you’ll be scrapping them against. Make sure you’ve got a pan under the car before you pull the pump as you’re going to be dumping all sorts of coolant all over the place. If you’re lucky, you won’t even drop any tools in it!
When I removed my old pump I noticed it did have corrosion on the impeller fins, so I was slightly justified in my replacement. Make sure you line the new gasket up with the bolt holes carefully before you have the new pump in place. Replace the bolts (have fun!) tightening them to “tight enough for threading into aluminum” and you’re done. With that part anyway.


Next up is the thermostat, which is held in place by three 10mm bolts. The top two are pretty easy to get to with a ratchet and small extension, the bottom right bolt is annoying and there isn’t much room to work. A bit of patience and you’ll have all three out, more coolant for your catch pan. If you haven’t already, detach the large upper coolant pipe and the smaller lower coolant pipe from the thermostat. These are held in place by some quite annoying spring clamps.


You know the next part, line the new thermostat up and bolt everything back into place. At this point you’ll also want to put the pulley back on the water pump. For now you only need to have them in finger tight, as far as you can get them without frustrating yourself too much but enough that they’re not touching the engine bay side or getting in the way of the new belt. If you need to, you can use two wrenches to hold one bolt while you tighten another, it’s a giant pain but in my case I couldn’t slip the belt over the tensioner with the bolts in the way.


Next up are the belts! I cut the a/c belt and removed the serpentine. The a/c belt is easy to get to if you remove the passenger side wheel and the little plastic cover that keeps debris out of the belt. I didn’t do that, too easy. The serpentine belt is pretty easy to get back into place, just snake it around until it looks right (you did look before removing it right?) and Google a picture of how it’s supposed to be laid out if you get confused.


I went ahead and replaced the tensioner pulley and then the tensioner assembly. Once the tensioner is in place, you’ve got the fun task of holding the tensioner as far towards the fire wall as you can while simultaneously lining the belt up. For this part I used a ratchet as it was the only way I could get the belt past the tensioner bolt and then hold the tensioner forward. Fun!


You’ll get it eventually, and then you’ll feel pretty damn awesome about it.


Take a look at the tensioner assembly, it’s got three marks on the tensioner arm and a single mark on the tensioner assembly itself, this is too give you an idea of the life left on the serpentine belt. Mine was previously showing just a hair north of the middle mark. After getting the new belt on, the indicator was showing at the bottom mark. Sweet!

Now comes the a/c belt. If you have a friend helping you out, make them do it. It takes a bit of work since it’s a stretch belt, I kept getting the first few threads of the belt on the pulley which would stop any further progress. Isaiah was also working on his truck so I was able to grab his help on this. We ended up basically holding a flat screwdrivers over the bottom pulley until we had it lined up well enough to move the screwdriver and let the belt threads fall into place. It’s hard to describe but it worked well. We did end up taking the side shield off so we had better access for this, we also broke pretty much all the bolts as they had rusted in place.


Just like that, you’ve got new belts, a new water pump, and a new thermostat. Again, I’d encourage you to buy an OEM thermostat or the replacement may be temporary. Anyway, take the car for a shake down run and if everything holds together than enjoy having a slightly more reliable ride. Over the next few weeks keep an eye on the coolant temp as you drive, and check the coolant level so you can catch any issue that arise. That’s how I caught my thermostat issue without really messing something up, plus it’s a good habit.

Until next week!

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