SX6 overheating - what should I be looking for?

by Rob

Kaeser SX6 rotary screw air compressor (Photo:

Kaeser SX6 rotary screw air compressor (Photo:

I bought this unit used about a year ago.

It has been working fine (other than burning through several belts)....but suddenly is overheating.

It will run for a few minutes after turning it back on, but then shuts itself off and illuminates the temperature icon on the control panel.

It appears to be low on oil, so I've ordered some Kaeser oil.

I also cleaned the air filter (which was filthy!)....What else should I be checking for as I wait for the oil to arrive?

I'm using my backup compressor in the meantime!

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May 29, 2013
Oil Change
by: Carls421

Hi Rob!
Sorry, I didn't see your previous message. Hope I can help. Ive had to answer with 2 separate messages, too many letters, sorry!

The following looks complicated but it really isnt.

First of all cleaning the cooler is basically getting your airline (Air Gun) and blowing out the cooler. The cooler is the part that looks like a car radiator, normally it is grey in colour or if you have the exact model as you have pictured above, it may be black, it has cooling fins.
Whilst the compressor is in normal operation, it sucks in the air by the fan, through the filter mat which should take the majority of the dust and crud. It cant take it all away so it sometimes gathers and clogs the cooler, so just blow it out from the outside inwards (opposite way to its normal direction) but use a mask when doing it, it can get quite dusty.

OK, Oil change, please do this step by step, but here's some info before you do anything. Please identify the parts I describe below before you start and whilst the compressor is turned off. Then follow the steps below.

The Oil can only be removed by pressure, you have to pressurize the "Separator Tank" (Where the oil is) to remove it. At the bottom of the Separator Tank is, as you said "Looks like a special tool" i think you mean the brass fitting?
That is just a push fitting, where you connect an airline hose to it. You will need a spare coupling that plugs into it, with a spare piece of airline (made long enough so it will reach from the fitting to a waste oil container) On that fitting there should be a drain tap that you can turn 90 Degrees. You should have one of these that was supplied with the compressor from new, either at the bottom of the compressor OR inside the door where the electrics are.

You need to identify where the "Combination vent valve" is on your compressor. This is the thing that when your compressor has reached the correct pressure, you hear an audible hisssssss, that hiss you hear, is venting the separator tank of air through the air filter. The combination vent valve you are looking for also has what looks like a tap that can turn 90 Degrees, and indeed it does turn 90 degrees. This is part of the oil drain process, it is that tap that pressurises the tank.

May 29, 2013
Oil Drain
by: Carls421

Identify the pressure gauge that is connected to the separator tank.

Step 1. Plug your made up piece of tube into the fitting at the bottom of the separator tank, before you switch the compressor on, DONOT TURN THE TAP YET (Or you will get very messy!)

Step 2. Switch the compressor on so it is running, try to run it so your oil is warm/hot.

Step 3. When the pressure gauge (on the SEPARATOR tank) is at around 7 Bar (100 psi) turn the tap (on the COMBINATION VENT VALVE) 90 degrees, then switch the compressor OFF by pressing the off button.

Step 4. Isolate the compressor, so no-one can accidentally switch it back on again (Emergency Stop) AND at the wall.

Step 5. Your separator tank pressure gauge should still be reading pressure. Hold on to the end of your made up hose tightly and point it into your waste oil container then SLOWLY turn the tap at the bottom of your separator tank, your oil should then come out of the hose under pressure. Be careful, because when your oil has nearly all been drained, your hose will judder when air starts to come out. When this happens, turn the tap off again.

Step 6. IMPORTANT!!!! When your oil is drained TURN THE TAP ON THE COMBINATION VENT VALVE TO IT ORIGINAL POSITION!! You will hear the hiss. This is VERY important because at the moment, you have potentially high pressure in the oil system. If you don't vent it and you try to remove the oil filter or do the next step, you WILL get high pressure hot oil in your face. I know from experience when I first started, It really hurts!!! :(

Step 7. When you hear the hiss stop. You just need to drain the cooler of old oil, this is simply a bolt at the bottom of the cooler which you remove and catch the old oil. Be careful putting the bolt back in, as it is very easy to cross thread, the cooler is only aluminium, the bolt is made of steel.

Fill up the separator tank of oil again, I usually go over the oil sight glass a bit because you need to put a little extra oil in, the fill the cooler again, check this after the compressor has run for about an hour in the normal way, if it needs more, then top up as necessary.

You will then have all your oil removed and replaced, at this stage you should replace your oil filter, air filter and filter mat. There is a rubber diaphragm and O-Ring in the combination vent valve that is replaced on the service also (4x chrome allen key bolts) and that is a full 2000 hour service complete.
You should replace your oil every 2000 running hours to ensure you dont have any wear problems.

Hope this helps. If you need anything more, please email me

Kind Regards


May 29, 2013
Carl, are you out there?!
by: Rob

Hoping you can help me identify how to drain the oil, and what the cooler line looks like that I need to clean out.

Thanks in advance,


May 23, 2013
Same guy, same question
by: Anonymous

So it's been 4 months, and now the unit is overheating again. The last time, I only added oil...didn't do a full oil change. My question now is, how do I drain the oil in a SX6, and what other lines should I clean out? I see a drain bolt on the under side of the oil tank, but it seems like maybe a special tool to fit in a real tight space? Please help!

Feb 12, 2013
by: Anonymous

Yep, oil seemed to do the trick. I'm back up and running! Thanks for your hep :)
Way to go, Carl. You have my thanks too.


Feb 06, 2013
by: Carls421

Hi, The oil probably is the cause of your overheating issue and also probably the cause of your belts snapping too, as your pulley would have been getting very hot through heat transfer and degrading the belts.

After you replacing the oil (i would give it a full oil change) Its best to make sure the cooler is clean, just use an airline to blow it out.

Changing the filter mat and air filter would help a lot if you said it was filthy.

Pretty much the only thing left is the oil filter, and you have given it a 2000 hour service! So you might as well do that too.

If you do have any more problems you can reply to this message and i would be happy to help, i am an ex HPC engineer so glad to help
Thanks much, Carl. Bill

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Jun 09, 2013
Back pressure
by: Carls421

Are you sure the machine is a CD75? and not a CS75?

A back pressure alarm usually means the separator tank (where the oil is) is under pressure for too long after the machine goes off load (stops making air)
This is can be caused by a few things.

The combination vent valve may be faulty, there is a rubber diaphragm inside this, which should be replaced every service. Possibly faulty.

A way of checking this, is start the machine, let it get to pressure, then stop the machine. Look at the pressure gauge which is attached to the separator tank. Does the pressure go down? How fast? It should vent and you should hear it venting. If not, then check your combination vent valves operation, if it has a solenoid on it, check the voltage. Maybe take the solenoid off whilst it is supposed to be venting, if it vents, then make sure the cable TO the solenoid has voltage going to it, it may be that the controller isnt telling it to open. If it is, hen replace the solenoid.

MPV (Minimum Pressure Valve) could be faulty and leaking air past it. Have a look at that. BUT BE VERY CAREFUL!!!! Make sure there is absolutely NO pressure in the system before you start undoing bolts!! Although the machine may say 0.0 pressure, there may be dangerous high pressure in the system! Maybe have the MPV serviced (replace the seals) this should be done every 8000 hours of operation.

Try those things and let me know how you get on

Carl, once again, thanks so much for your contribution.


Apr 17, 2013
by: Anonymous

I suppose that you have checked so it runs in the right direction?

is it a belt-driven model with one flat belt? Sometimes you can get the alarm "3" backpressure if the belt slips. If the belt is tensed and the belt pulleys seems ok and not worn out, check the back pressure sensor (it´s mounted on the intake valve, just two wires and a rubber hat). Put out the current first, as you may burn up the sigma control if you ground one of the wires by mistake.

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Critical Error 300A

by Saurabh
(Pune, MH, India)

Getting Critical error 300A on the control panel display of the compressor. Does anyone has any idea what this error is and how to get around this error.

Urgent solution needed.

Thanks in advance.

Comments for Critical Error 300A

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Dec 29, 2012
Problem with compressor critical error 300A
by: Fernando Villanova

Could anyone tell me if critical error 300A may
be solved through other ways than changing the controller? if so, what I have to do in order to solve this problem? Thanks in advance
Fernando Villanova

Dec 22, 2012
Which compressor?
by: Carls421

Is the fault on a Kaesar compressor? Is the controller a Sigma? Please could you tell me details, then should be able help you.
If it is a Sigma controller then you would need to contact Kaesar to get them to K-load it (reset the computer inside)
You can switch it off for 10 mins then try again, this should work for a short while, but it will come back.
Otherwise you will need to replace the controller which can be very expensive

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