Coolant reservoirs in my previous vehicles has never really been hot, but I was recently doing some work in the engine compartment of my 2013 M5 and noticed that the coolant reservoir was really cold. I did some digging online and I've gotten answers ranging from its perfectly normal to really, really bad.

Personally, I'm just wondering if something's wrong with the thermostat?

How about other M5 owners, does your reservoir heat up or not?

 

The catch can (reservoir) really only serves to catch fluid which is ejected from the radiator. It then provides a source for the rad to pull/suck from when the coolant in the rad cools. If the reservoir is within the correct fluid level range and the rad is also pretty much full it should be fine. perhaps you don't get the engine hot enough to eject fluid or the rad has an air gap at the top(under the cap) that is sufficient it doesn't need to eject fluid. I think most of the heat on the reservoir is from other engine sources and the fluid in the reservoir is not part of the circulation system, except to catch what is ejected from the rad and permit it to return to the rad when the engine cools.

 

WT eff??? ^^^ hahaha????



To the OP if you feel there is a coolant temperature issue you need to do some basic testing using a Handheld Digital temperature device.
Depending on the ambient and if your engine has reached operating temperature, your reservoir should be close the temperatures of the return hose with no cooling system issues.
Make sure when testing that the AC is not on and that the clement control is off and not on heat settings.

Because your year is OBDII you can also connect to the diagnostic connector with a Diagnostic scanner and read live coolant temperature information going on a short drive. Depending on the ambient and your vehicle speed which can affect the IAT and some slight degree changes in the normal run temperature. Make notes and this will help conclude if there is a cooling system issue.
There are other tests, but these are the east for most DIY to try.

 

I just want to make sure nothing is wrong. This vehicle was purchased in a state of disrepair and I've been putting it back together slowly. The problem with doing that is that you expect anything and everything to suddenly break apart at any given moment.

I did drive it for nearly an hour, including twenty-minutes of 65mph on highway, and when I got to my worksite for the day, I checked it real quick and the reservoir was as cold as the metal of the body. I know it doesn't take heated fluid directly from the radiator but it seems to be unusually cold anyway, especially given how it's late March and I live in the NE.

I will probably have my local mech check the ECU next time I come in for work. Just to be sure. Thanks for the suggestions.

 

I'm assuming you have checked the fluid level in the radiator? If it's low it is less likely to push fluid to the reservoir tank.

 

It does not work that way....


PrimusAnimatus if your coolant temperature gauge is in the proper position after you get the engine to normal operating temperatures, if your heater when the temperature is set to highest level and the blower motor turn on full is blowing hot air, if you have no coolant leaks or smell coolant, then you are halfway to the point of a no problem.
Honestly if you look at your year MAZDA's coolant diagram and how things warm up nothing so far has my concerned with tell you, you have an issue. However, prudence does have me recommend having the ECU scanned in the area's I suggested. You can also get a coolant test to see the condition and current mix of coolant to water but that will likely cost you and at this point not really need.
The other thing is without a handheld digital temperature meter it's really hard to determine true temperature values in various areas of the engine. The reservoir is not one of the first area's I would be looking at at.

I might add that AIR in your system is not really possible because of how the engine and cooling system is engineered. Even if you R&R the coolant it will still self "burp" any air in your system.

Keep in mind I don't have your Mazda here physically to check all your concerns and my response is based on the limited information you are providing.

ASE

 

Perhaps you can educate us as to how the system works?

 

It not relevant nor helpful on forums like these and not a short training. Best advise if you are really interested (which I don't think you really are) is to go to MAZDA OEM or MAZDA REAL PART and look up all the components and parts that are in a HVAC and cooling system. Then go and see if you can find all the related sensors that give the ECU input so the ECU can adjust several operations for the engine and transmission.

Most Certification classes having to do with both are generally 5 days long. And that is not for the ECU/TCM/PCM etc., which takes a bit longer if you class also include programing "THOERY", training which all work together in HVAC and cooling system

ASE

 

Actually I am interested in what I've missed while working around these rudimentary systems since they first appeared. I admit to typically working on vehicles of older vintage, 2013 and down but have yet to see sensors controlling or feeding data to the ECU respecting the flow of coolant to/from the reservoir tank. This system is really quite simple!
Also, I certainly don't participate in forums where sarcasm is the norm, which is quite another language altogether. If I somehow stepped on your toes, I apologize, it was never intentional.

 

No one steps on my toes and many responses are entertaining to me. Because you can't see my body language or demeaner you can't see I smile or laugh often on many vehicle forums with the none sense that so many DIY or crowd consensus thinks things work in the real world.
I also participate on many forums not all auto related to give advice and suggestions and on all of them there is those members that basically have no real to mention mechanical experience in the way of actually training and education and even some self-taught with a full and dirty toolbox mechanics that will challenge some of my responses. LOL
But then some just like to do it wrong the first time and like to take the Long Way Around to doing service procedures.
As for what you call "rudimentary systems" supports some of my above comments. LOL