VZ Commodore Alloytec Overheating Problem

[commford1]

Hi guys,

Hoping someone can help shed some light on this issue which is driving me nuts.

My VZ has been running quite warm for the last couple of months when it's driven for longer than about 20 minutes.
It use to run at around 1/4 on the temp gauge but now gets to about half way but continues to get as high as 3/4 and just above before it miraculously does this two stage drop in temp.
What I've also noticed is that when it gets to 3/4 on the temp gauge, if you drop it into 3rd gear (which causes the revs to obviously increase), a few seconds later the temp starts to come down as per the below video link and return to where it once operated.

[video=youtube_share;aEeXn5_9LxE]http://youtu.be/aEeXn5_9LxE[/video]

Just some background to this - the radiator was replaced a few months ago, along with the radiator hoses and then the water pump started leaking so that was replaced with one from super cheap auto. I don't know if it's a coincidence, but the higher temp started soon after the water pump was replaced.

The system was purged of air traps, it's not loosing coolant, not boiling over and the cooling fans seem to be operating without a problem.

The thermostat hasn't been replaced, but I don't know if these symptoms relate to a faulty thermostat.

Any advice/previous experiences with similar problems would be appreciated.

Thanks all.

 

[akarshmalikal]

Hey Bro,

The same issued i faced few months before the temp gauge went over 75% and i was stuck in traffic suddenly i kicked the A/c on then it came back to normal..
There was 45% air trapped in the cooling system. Once i bleed it out then it was working fine..

About your issue u have to check for the air trapped inside the cooling system and replace your radiator cap with the genuine gm part as its kinda cheap. As much i guess this is not the problem with thermostat..

You can bleed it your self.. if u don't know let me know Hope your commodore get fixed soon

 

[diysv6]

Have you purged the cooling system with the "heater" operated and AC not running? An air lock could be present in the radiator heater block under the dash.
Have you checked the heater tap is actually opening/shutting physically?
Are the input output hoses at the heater tap running at the same temperature?
Can you feel very hot air coming through the eg demister ducts etc? .

If you are certain all air is purged and the overflow tank operation is correct, system fans are running correctly, then I would consider the thermostat.
A sticking thermostat could be the culprit. Maybe debris from the old radiator core, hoses, or gasket material from the old water pump etc could be hindering the operation of the thermostat. A big maybe?

Most earlier engine designs have the thermostat on the hot side of the cylinder head/s. My understanding is that the alloytec seems to have the thermostat at the input to the cylinder block on the cold input side from the radiator. To my mind this means that there has to be water always "sitting" in and around the thermostat housing cavity to even get some thermal response from the thermostat. ( A totally empty overheated engine block would probably destroy the wax pellet in the thermostat. However as designed, the alternate bank firing cooling sequence would be invoked by the ECU - hope I never experience that problem).

The engine temp sensor is near the oil filter on the engine block, not the cylinder head areas, and some distance from the thermostat. (Not like in the older conventional locations like the cylinder head, and most times close to the thermostat housing).
In the non alloytec motors, most people wait for the thermostat to open at the cylinder head and feel for the almost instant hot rush into to the top of the radiator usually whilst slowly topping up the radiator. The alloytec thermostat has to get hot to open, which in theory suggests the engine block/heads are at coolant operational temperature, but the rest of the cooling system has to have been primed with no air locks. eg. heater needs to be evacuated as well as the engine block/cylinder heads, radiator full, so that the rush of hot water represents the full coolant capacity, not the diminished capacity with air locks.

Does this help with explaining why the temp gauge reads high then when the block gets hotter from the increased RPM in 3rd gear, something occurs to get increased water flow and drop the engine temperature? Or maybe the second cooling fan is cutting in ?

 

[commford1]

Thanks for the reply buddy,

The only way I know how to bleed the system of air is to loosen the plastic screw on the top of the radiator until coolant starts coming out. I checked it again last night and as soon as I loosened it only coolant came out.
Am I missing something?? (I hope I am)

 

[commford1]

Thanks for the explanation dyssv6,

I checked the heater tap and it seems to be operating. I'll follow some if your other suggestions on the weekend.

When I got home both fans were running, so I know they're both kicking in (not that they should have been after a short drive).

 

[diysv6]

Once you focus on the thermostat you open up a long home handyman job or an expensive mechanics repair.

So, if you have the time and perseverance, looking around for other possible causes is worthwhile.

When the engine temp gauge reads high is there really a smell that the engine is indeed getting very hot?

Could your engine temperature sensor have a loose/broken connector or is the sender faulty?
I think it uses the ECU/BCM to drive the dash temp gauge and also switch in the AC fans where required.
I checked mine some years back as I suspected the second fan was not cutting in. Luckily it was.
Have not located it in my Haynes manual as yet.

Its located just behind the oil filter body.

 

[Trevor 062]

Have you tried changing your radiator cap

 

[commford1]

Thanks for the tip - the radiator cap was changed about 6 months ago after the old one started developing a crack.

I tried bleeding it again (with the heater on hot) but water comes straight out and no air from the bleeder screw.

There's nothing else to change but the thermostat right?

 

[commford1]

I wouldn't say there's a distinct smell as such but it feels warmer than I would normally expect it to feel, even on a cooler day.

 

[Benboy]

Have a read of the accompanying attachments for detailed instructions on bleeding the system. I suggest, if possible, that you raise the front of the vehicle (use ramps or sloping driveway) to expedite the process of expelling air form the coolant:

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Good luck.