Ok, so I noticed that I had a bit of an oil leak around the oil cooler after I rebuilt the engine. After giving the outside of the cooler a good clean, managed to track down the leak to be originating from the thermostat fitting. Figured that the crush washer might have failed, so replaced it today... Started leaking even worse!!!

Wire brushed the corrosion around the thermostat fitting and had a closer look. Found oil leaking from a pinhole just above the crush washer . Conclusion is the oil cooler fitting must've cracked at some point in time and in changing the crush washer, I probably made the crack propagate further...

My question is whether its possible to have the crack repaired (TIG welded or something) or am I looking at buying a new or second-hand oil cooler? Has anyone else had this problem before?

Thanks for reading!

Cheers,
- TT

 

A competent welder can tig weld it. You will need to make sure you clean the cooler very well before and after the welding.

 

It's probably just cheaper to buy a used cooler. TIG welding that area will be challenging and then the boss will have to be machined again.

 

Ok, so I made a few enquiries, and it looks like the cheapest option is to have the cooler repaired... But here's the real complication:

I have a slight issue of a sloping driveway where I live. I have a garage at the end of the driveway, but it is too short to fit a car into. There is just enuogh flat ground leading into the garage so that I can do work on the car during the day, but I can't leave the car up on stands overnight (as the garage won't close)...

That being the case: is it possible to remove and re-attach the oil cooler with the car on the ground? I was thinking of removing the front bar, in the hope that it'll give me better access. Just want to get your opinion on this before I go ahead & do it...

Thanks for reading.

Cheers,
- TT

 

you should be able to get it off without having the car off the ground. its only 4 nuts that need to come off. i would soak them in PB blaster before you try and take them off as ive never had any luck not breaking off the studs

 

Thanks, 87 t-66. Was just about to post a self-correction lol. Yep, can be done without even having to remove the front bar! All I did was remove the two plastic covers around where the overflow bottle sits & that gave me access to the top banjo bolt.

Definitely agree with the PB blaster on the studs - soaking them as I type. From the amount of corrosion in the area, I'd be damn lucky to remove the cooler without breaking a stud or destroying a nut...

Cheers,
- TT

 

Meh, the mounts are a few dollars from the dealer and your old ones are probably dead already. Snap those studs off and don't waste time doing it.

I had another thought on the cooler. If you can get a -10 AN flare welded on you won't have to have machining done. Then make up a braided stainless line with AN fittings to attach.

 

when i snapped off the studs i went to the dealer and they say the mounts only come with a new cooler so i drilled out the old studs and put bolts through

 

Thanks for the advice, guys. I actually managed to find a radiator shop that's fixed a few oil coolers off FC's that've cracked in the same way. Aaron, I'm not too sure what you meant with by welding a flare and attaching a braided stainless fitting... It's the thermostat fitting that's cracked, so I'm not sure where the additional SS line comes into it... I'm assuming that would work for the banjo fittings? The guy at the radiator shop said that they'll just put a new fitting onto it, so I guess there's no getting away from machining it.

Yep, snapped all studs off except for one while removing it today, despite thoroughly wire brushing as much rust off the studs as I could... I'm not even going to bother asking the dealer how much they want for new ones. Like you said, rx-711, I'm just going to drill out the studs and replace them with bolts.

Cheers,
-TT

 

Oh, thermostat fitting. It thought it was the line fitting. In that case there's probably no choice but to weld and machine it.

 

Got a call from the radiator shop today... Doesn't look like he'll be able to weld the thermostat fitting because the crack is too deep

However, he said that if I can do without the thermostat, he'd be able to cut out the fitting and weld a piece of plate in its place.

I can't forsee any serious ramifications from removing the thermostat and blocking up the bypass hole with a bolt. Can anyone correct me on this? What's the worst case scenario - that the oil will be colder than average on startup?

Thanks for all your help with this issue.

Cheers,
- TT

 

Well, for one thing, if you remove the thermostat and weld a piece of plate on the bottom of the cooler, your oil cooler will now be useless.

If the thermostat is removed, oil bypasses the cooler.

To properly remove the thermostat, you need to plug the bypass hole inside the cooler.

Aside from that the only real issue is that it will now be hard to maintain oil temps. You may increase engine wear by keeping the oil out of it's operational temp range, and it will take FOREVER for it to come up to temp.

 

Why didn't you just buy a used one? They're a dime a dozen.

+1 for thermostat = necessary. do it right.

Mazda does sell the rubber seperately, but list is $42 each and they're $25 each even with my mazdaspeed discount.

Needless to say, I just bolted the cooler straight to the car.

As far as the crush washers go, you can re-use them only if you re-anneal them. They will seep otherwise.

 

Well, I thought I'd try & plug up the bypass valve and remove the thermostat (the radiator shop was going to charge me anyway, so I though I'd give it a shot).

If I didn't accomplish anything else; I managed to prove that the thermostat is necessary...

After I put it all back together & started up the car, the oil pressue on the stock gauge stayed half way between the 0 and 4 indicators - significantly lower than normal (stays at 4). Didn't run it for long, coz it didn't feel right.

I guess the thermostat is more so in place to maintain the oil pressure (i.e. shortest path of travel, unless REALLY necessary), but hey, hindsight is a beautiful thing.

Unfortunately, since FC's aren't all that common around here, second hand coolers are 1) not easy to come by and 2) not cheap ( at least ~$200 for a functioning one from a wreckers). Hence why I tried everything to get mine fixed

Thanks for all your input with this guys!

Cheers,
- TT

 

That has not been my experience, Aaron.
Removing the thermostat (and plugging the bypass hole) was one of the things I did this summer whilst chasing an oil temp problem and I've been running that way for nearly three months now.

Admittedly, I haven't had full winter conditions yet- although she's had frost a few mornings (and snow in Nebraska)- but the time needed for the oil temp to rise has not been appreciably lengthened.
Maybe a few minutes longer but hardly forever.

Obviously, I'll have a better idea next April but so far I'd much prefer running without a thermostat than running with a malfunctioning one.

Hindsight is pretty indeed but your conclusion here is really ugly.

Assuming that your thermostat is fully functional, it blocks off the bypass at @145°F- at temp that your oil will exceed in a matter of minutes- which means that the normal condition is for the oil to be forced through the cooler.
You seem to conclude the reverse- oil bypasses unless extreme conditions (or as you put it, "REALLY necessary") exist.

So, most of the time- save for the first few minutes after a cold start- an oil cooler with a functioning thermostat is acting exactly like a cooler with a permanently blocked bypass, so linking a perceived change in oil pressure to this mod doesn't compute.

In other words, the thermostat only affects oil temp, not pressure, so you'll have to look elsewhere to explain the change you saw.

 

The thermostat serves a number of purposes.

Obviously, Mazda wants the oil to heat up quickly for emissions purposes.

It's also there to help prevent the oil cooler from "inflating" if thick oil is used in cold weather. The front cover bypass is also part of this system.

I guess except in cold weather the thermostat doesn't effect warmup times. Certainly in Australia it won't matter in that sense.

 

The "inflating" cooler is a condition I've never heard of but it kind of makes sense and I suppose Mazda has to account for every possible situation.
Obviously, running the appropriate weight oil for conditions would eliminate the possibility of blowing up the cooler due to overly thick oil.

As I said before, this will be my first winter with the deleted thermostat and since my car is a daily driver I should know fairly soon how it works in sustained colder weather.
If anything untoward occurs I'll let ya'll know.

 

dang i should have kept my oild cooler to sell uggh

 

Interesting argument, clokker. Similarly, my justification for removing the thermostat was that because the climate here is warm, I was almost certain that the bypass would close very quickly after start-up anyway... It wouldn't take long for the oil temp to hit 63°C when the ambient is 40°C in summer.

However, I'm yet to come up with an explanation on why the oil pressure has dropped after I plugged the bypass and removed the thermostat...

Clokker, did you see a drop in oil pressure after you removed your thermostat? BTW, thanks for the info on your setup - I've got some confidence now that this might just work.

Cheers,
- TT

 

No, oil pressure remained the same.

Replacing the bad eshaft thermopellet raised pressure significantly however.