Today we are looking at what is involved in replacing the inlet manifold gaskets on a VN to VR V6 Commodore. Although this job is not particularly difficult, it is quite time consuming so allow yourself a few hours to get it done.
As usual please read through this article in it’s entirety before starting out so that you get an understanding of the steps involved and to ensure you have, or have access to, the required tools and equipment needed to complete the job.
As well as a Inlet Manifold Gasket Set there are a few ‘extras’ that should be added to your parts list. For example, it’s always a good idea to replace the Thermostat after it has been removed, it’s also a good time to give the manifold and the throttle body a good clean so Throttle Body Cleaner and Degreaser can be added to the list, there are two plastic coolant hose fittings in the manifold that are often brittle and break when the hoses are removed so pay a visit to your Holden dealer and they will be able to help you out there and finally the V6 MUST HAVE coolant of the correct type so check for compatibility before deciding on a coolant.
I think that covers the formalities so let’s get stuck into it.
The first thing you want to do is drop the bottom radiator hose off at the radiator to drain the coolant. Obviously do this away from where you are going to work unless you want to slosh around in water for a couple of hours 🙂
Next up we need to depressurize the fuel system. To do this we remove the fuel pump relay, start the car and let it run until it stalls and then crank it over a few times to bleed off any remaining pressure. Refit the relay when you’re done.
Then we can remove the negative battery terminal (after making sure you have the security code if the original radio is still fitted) and remove the top radiator hose and hard vacuum lines from the throttle body to the charcoal canister.
Now the air intake and filter can be removed. If you’re not already aware, as well as at the filter box and throttle body, the air intake is secured with a bracket and 10mm nut halfway along.
Next we can remove the right hand side (drivers side) spark plug leads from the coil packs and move them over to the side, out of the way. The lead/cylinder numbering is shown below.
The next step is to remove the drivebelt. To do this we use an 18mm spanner and rotate the tensioner anti-clockwise. For installation purposes a picture of the belt layout can be found HERE.
Removing the alternator is next on the list. The electrical connections consist of a 13mm nut and washer on the main wire and a wire-clip terminal.
And it is mounted by a 13mm and a 10mm bolt…
Once the alternator is lifted out of the way you will find the temp gauge sender and the ecu coolant temp sensor. You will more than likely need to use a flat blade screwdriver to push the wire clip up to remove the connector from the coolant temp sensor.
We can now remove the coolant hose next to the senders. A plastic fitting hides under this hose on the manifold end (as I wrote about at the start of the article) so be careful if you don’t have a replacement. Also if the hose looks at all dodgy replace it! It’s a lot easier to do it now while everything is out of the way.
Now at the rear of the engine we can remove the accelerator cable and cruise control cable (if fitted). The accelerator cable has a 16mm nut and it needs to be wound to the end of the plastic thread. Once it’s there we can pull back on the outer of the cable and slide the inner cable through the slot in the bracket.
Then we can ‘curl’ the cable around and pull the end from the throttle. The cruise control cable is held on by a clip that just needs the centre pulled up slightly to remove.
Now we can remove the cable brackets which are secured to the throttle body with 10mm bolts. The rear-most bolt also holds the fuel pump regulator bracket.
Next up, remove the small dash vacuum supply hose, the brake booster vacuum hose and the fuel return line.
Still working at the back of the manifold we have to remove the connector from the manifold air temp sensor and there is also a plastic ‘clip’ securing the wiring harness to the manifold in the same area that needs to be pulled out as well as another coolant hose connected to a plastic fitting in the manifold – be careful removing the hose!
Now we can remove the fuel injector wiring. Once again the wire clips can be pushed in and the connectors lifted off each injector. Carefully pull the drivers side injector wiring over to the passengers side of the engine to get it out of the way.
Next on the list is the throttle body wiring, the fuel supply hose and the MAP sensor vacuum hose at the rear of the throttle body (hidden in the below pic – arrow indicates it’s approximate position).
The next step is not critical, I just like to do it so I have no issues when it comes time to refit the manifold. The bracket that the larger of the two alternator mounting bolts goes into can be removed. It has two different length 17mm bolts securing it and you will only get to the rear one with a spanner. As I said it doesn’t have to come off so please yourself.
Before we can start on removing the manifold bolts the thermostat housing has to come off so that we can get to one of the them. Two 13mm bolts secure the thermostat housing and it’s a good ideas to remove and replace the thermostat while you’re at it.
Also be sure to clean the areas around where the manifold mates to the cylinder heads and the block, the last thing you want is crap falling into the engine as the manifold comes off.
Now we can remove the manifold bolts. There are five each side and the bolt head size is 3/8. With all the bolts removed the manifold should only need a gentle tap to loosen it and then you can lift it up and out. Try to keep it as level as possible so you don’t end up with coolant everywhere, although you will have to tip it up slightly at the front so the throttle body clears the firewall.
Before going any further I suggest laying a rag in the valley of the engine to keep any crap out while we clean the gasket surfaces. A single-sided razor blade is good for this and spend as much time as you need to ensure that the cylinder head surfaces in particular are as clean and ‘flat’ as possible. Also, be careful to keep as much muck as possible out of the coolant passages and intake ports while you’re cleaning the surfaces.
I recommend giving the manifold and throttle body a thorough clean but be careful of the plastic hose fittings each end. If you have access to a wire brush the thread on the manifold bolts could do with a going-over and the corresponding threads in the cylinder heads should be cleaned out carefully also.
From factory the bolts have Loctite or some sort of thread locker on them, I choose not put anything on them as they will need tightening occasionally (possibly from gasket shrinkage) and as they screw into a blind hole I don’t think any sealant is necessary either.
The cylinder head to manifold gaskets should have locators that fit into corresponding holes in the heads and the two valley gaskets will only go on one way and ensure that they are pushed right into the corners where the cylinder head and block meet. It is also a good idea to put a smear of sealant in this area as they can leak without it.
With that sorted you can now carefully lower the manifold into place and CHECK THAT THE GASKETS HAVEN’T MOVED before fitting the manifold bolts. Start all 10 manifold bolts a few turns before you tighten any, you may need to move the manifold around a little to get them all started. The correct way to tighten the bolts is to start with the middle bolt on each side and work your way around evenly and then recheck each one. The correct torque setting is 8 – 15Nm, if you have a small torque wrench you could torque the bolts you can get to with it to get a feel for how tight they should be.
From here it is simply a matter of following the steps in reverse while taking note of the following points –
- Once the manifold is fitted and the bolts tightened refit the injector wiring harness to the drivers side of the engine, doing it now is a lot easier than when everything is bolted on!
- Double-check that all vacuum lines, electrical connections and fuel hoses are fitted before starting the engine. It is very easy to overlook one believe me!
- When it comes time to refill the coolant undo the bleeder (from memory only on the VR) to ensure that you don’t get an air lock in the system and once started and run check for oil and coolant leaks and ensure that the cooling fan is operational once the temp gauge reaches around halfway.