Where's the radiator water going?

[tim04c5]

I'm dealing with a 2016.5 CX-5. 117K miles.

The water level in the radiator is dropping. Maybe 16 oz. per a few hundred miles. Mechanic doesn't know where it's going. He pressure tested without finding a leak. He wants to replace hoses. Stands to reason if hoses were bad, it would've leaked during the test, right? No leaks are visible after driving it.

Also the level in the recovery tank is at normal full. He doesn't know why it isn't refilling the system.

Other than finding a new mechanic, the mystery is where the water's going? This doesn't sound normal to me. I'm a pretty mechanical kind-of-guy. but I wasn't a mechanic by trade.

Thanks for any suggestions.

 

[HyFlyer]

The Mazda skyactiv auto transmission uses a heat exchanger that involves the radiator. Check your tans fluid too

 

[tim04c5]

In this situation, it appears that the amount of water added to the radiator, in the number of miles driven, that there'd be some evidence. Such as in milky looking oil? Or? The oil looks normal.

 

[PTSanchez]

There are 2 types of fluid leaks: viscous & permeation.
Both leave a trail.
With that high odometer reading, this vehicle should be on at least its 2nd set of soft hoses ..... so, do you have the maintenance records?

If the coolant recovery/overflow bottle level isn't fluctuating, the system's airtight integrity is gone - so start by checking both caps, all connections & hoses for residue, stains, drips, etc.

It's also possibly a permeation leak in the radiator or any hose, a leaky heater core, a cracked head, or failing head gasket as well, so perhaps do a compression test ....... & while they're out - check all 4 spark plugs for color consistency: if any 1 plug is extremely clean, you've found the leaky "hole".
If so, please be advised that there's only 1 way to repair it.
G' luck!

 

[tim04c5]

Thanks @PTSanchez. Need to start checking things.

It's my gal's car since new. They're original hoses.

Is the repair of the heads? Engine removal?

 

[PTSanchez]

That's some good life for OE soft hoses!
At minimum, the head has to come off for both scenarios: a failed gasket or crack.

 

[tim04c5]

Going to start with replacing the hoses. I should know better.

 

[PTSanchez]

The radiator cap (checked on a cold engine) is also a prime suspect here, & actually a no-brainer. Look for a shallow embossed/concave ring on the rubber seal disc, & any discoloration/dried residue outboard of that.

 

[PatrickGSR94]

With that high odometer reading, this vehicle should be on at least its 2nd set of soft hoses ..... so, do you have the maintenance records?

Totally unnecessary unless the hoses are showing actual signs of deterioration, i.e. leaking, cracking, hardened rubber, etc. Hoses typically need replacement with time, not necessarily a certain number of miles. That's why recreational type cars that might be older but with low miles, like Miatas, often need all hoses replaced even with only 50K miles or less on the car. But then I replaced all the hoses on my Integra at nearly 300,000 miles.

I have 138K miles on our CX5 now and the hoses still seem to be in quite good shape. No reason to replace them at this point.

 

[ceric]

In the case of my ex-98 BMW 540iA.
BMW ran that V8 engine hot to meet mission in USA.
When the hood was open, one could feel it.

All plastic parts/hoses deteriorated sooner than most.
One neck to radiator (new radiator assembly) and two hoses.
I got stranded three times on the roads.

 

[PTSanchez]

I replaced all the hoses on my Integra at nearly 300,000 miles.

I have 138K miles on our CX5 now and the hoses still seem to be in quite good shape. No reason to replace them at this point.

Famous last words: might want to memorize the info above & recite to the AAA dispatcher.

 

[madar]

The radiator cap (checked on a cold engine) is also a prime suspect here, & actually a no-brainer. Look for a shallow embossed/concave ring on the rubber seal disc, & any discoloration/dried residue outboard of that.

The usual problem with these is the rubber seal on the underside swells up to be bigger than the radiator neck. This puts a lot more pressure on the system as it doesn't allow flow to the overflow tank, causes radiator and other leaks in the system.

 

[yrwei52]

Going to start with replacing the hoses. I should know better.

I’m with PatrickGSR94 that most rubber hoses for coolant system, especially those from Japan, are very reliable. The only exception is the upper (inlet) radiator hose as it usually gets very hot taking the hot coolant from the engine side. And that’s the only rubber hose I’d replaced on my 1998 Honda CR-V with 190K miles.

Honestly I simply can’t see replacing all rubber hoses without obvious sign of leaking would help your problem at all. Replacing the radiator cap may be is the first step to do as it’s easy and cheap. But I doubt it’s the culprit of your problem. It may help to suck the coolant back to the radiator when it’s getting low. If it won’t, the coolant system definitely is having a leak somewhere.

 

[PTSanchez]

A 1-oz. bottle of UV dye will go a long way here: https://www.amazon.com/dp/ (commissions earned)

 

[ColtX-5]

The CX-5's hoses are EPDM. They will last years and years and likely several hundred thousand miles. I wasted a lot of money replacing all the hoses in my 2006 Miata when I found soft spots in the 2 largest hoses. The rest were perfect.

 

[AVC]

Agree, I haven't replaced a radiator hose in 25 yrs. Virtually all OEM's now use EDPM or similar compounds, making those hoses essentially lifetime parts, unless a manufacturing defect, puncture, etc.

Now the plastic fittings OEM's use on the radiators and for coolant splits, I've replaced some of those over the years that have become brittle due to heat. Recently, a 20 yr old Ranger.

 

[PatrickGSR94]

Agree, I haven't replaced a radiator hose in 25 yrs. Virtually all OEM's now use EDPM or similar compounds, making those hoses essentially lifetime parts, unless a manufacturing defect, puncture, etc.

Now the plastic fittings OEM's use on the radiators and for coolant splits, I've replaced some of those over the years that have become brittle due to heat. Recently, a 20 yr old Ranger.

guess you haven't been around too many Miatas, which commonly need coolant hose replacement after 20+ years. All the OEM coolant hoses are still available, and many places even sell complete kits with all the hoses included. I did all mine when I had the engine out recently, and some of them were indeed quite crusty and gross. Glad I did them because a couple of them are known as "devil hoses", i.e. nearly impossible to access fully when the engine is still in the car.

 

[tim04c5]

Sorry I didn't update this thread.

I appreciate all of your suggestions!! It turned out to be the hoses. At first the mechanic said he pressure tested. I ruled them out because of this.

We're currently looking for a new mechanic, lol...

 

[PTSanchez]

Thanks for the follow-up report.
Several new hoses + 1 new mechanic = Happy ending