Overheating M35

[sav man]

On the way to work this morning my M35 got hot. I waited for it to cool down, put it on a hill and topped up and bled the coolent system. The car was fine ideling for 15 mins, but when i drove up the road the temp needle started to go straight back up, so I parked it.

I've only had it overheat once before when the plastic bleed tap failed (now have a metal ball valve). So I want to test the thermostat, but I've read that the VQ engines have multiple thermostats. Is this true? And if so where are they all?

[PN-Mad]

There is only one on ours, and it's a triangular assembly where the coolant hose returns into the block.

There are other multiple thermostats on things like the pathfinder, located down in the Vee of the block, however that channel is just blanked off in our cars.

Obviously the simple stuff was looked at? They are notoriously hard to bleed. I top it up, close the cap, put the nose down the hill, and then put a hose on the rear tap/ball valve nice and high. Then it will take 15-20 mins to bleed once the car is at operating temp. Topping up as you go.

The rad top tank also is prone to cracks/seals leaking.

[sav man]

Why nose down hill and not up hill? I thought youd want rad above the bleed point?

I'm going to have a good look on the weekend

[Sydsyd]

Had the same problem last month, tried flushing the radiator with no success, in the end mechanic replaced the whole radiator, works wonders

[Brick]

Why nose down hill and not up hill? I thought youd want rad above the bleed point?

I'm going to have a good look on the weekend

the reason you want it down hill is that air rises. and as the bleed point as at the back you want the air to rise to the back.

[PN-Mad]

Yup, rear bleed point is higher than the rad neck. I artificially raise it up with hose and funnel, and it's a far more effective bleed point than the rad neck. Make sure your heater is on and pumping hot air out.

[GeeDog]

If it's the same thermostat as a 350GT, I have a brand new genuine nissan one in my garage. I bought it from the US and was going to fit to my 350GT, then some dozy prick thought sending a text was more important than watching the road & wrote off my car.

It has never been used, and includes a gasket. I paid around AU$70 delivered, happy to sell for $50 delivered (std post).

I've also got a 350GT radiator - replaced it with an alloy one to try & cure some overheating, but made no difference - hence the new thermostat.

[scotty nm35]

Pretty easy to test a thermostat, although I have never seen an oem one fail before. It won't open with water from the kettle though, it needs to be on the boil in a pot on the stove.

Most likely it just needs a good bleed, which can only be done cold and with the heater off from my experience. One cup of coolant missing is enough to airlock the stock system, which is why I designed my cooling mod for the block.

Have a search, there are plenty of threads outlining the issues and how to bleed the system properly.

[PN-Mad]

Heater on/ doesn't matter I don't think. There isn't a valve in them to stop the coolant flowing, is there?

Having it on is just a good indication that you haven't an airlock in the core.

[sav man]

I know the R series Skylines need the heater to full to bleed properly, as they have a valve to control the coolent flow. I've seen skylines turn their heater on after the system has been "bled" and have overheating problems cause a heap of coolent goes from the engine to the heaterbox. Things might have changed in the stag though.

I'll redo it from dead cold and see how it goes.

Scotty, do you still sell the coolent bypass kits?

[scotty nm35]

With the heater on, there is coolant rushing through the bleeder pipe, it causes bubbles of air to fill the system and can take ages to release defeating the purpose of the bleed.

Like I said, the final top up needs to be done with the car cold preferably, and the heater off. It might need to be done multiple times over a few days.

[scotty nm35]

Scotty, do you still sell the coolent bypass kits?

I haven't sold any for a while, but I think I still have enough parts here for another kit. It works pretty well from my last Sandown track experience, I lost over a litre out the overflow and the car still managed to stay cool on the way home.

[Artwear]

As a new stag owner this is a worrying thing to read, I assume day to day driving wont cause an issue? And if it were would standard mechs know n use these methods? Almost seems like moving to vic is the best way to keep these gals ship shape!

[scotty nm35]

Most mechs have their own way of bleeding, and won't let the car go until it runs fine on the test drive. They know the outcome if a dozy driver doesn't check the temp gauge on the way home, and changing head gaskets on these VQ's is a pain in the arse.

If you have issues, (and you shouldn't usually unless something fails) then you just need to take your time with re-filling the coolant. I have had some engines take hours to bleed, and others fill fine. The coolant mod definitely helps with filling, as it allows all the trapped air to evacuate the block quickly. I rarely need to re-bleed my car these days when refilling, as the overflow reservoir works as it should to top up the radiator.

You can usually hear when there is air in the system, as the heater lines make a waterfall noise behind the dash, and the heater may not blow hot, meaning there is an airlock. It will usually overheat within 1 or 2km if the airlock is bad enough.

Shame Nissan designed such a poor cooling system, but our turbo Stagea is worse than most VQ's, due to the turbo lines boiling the coolant in the turbo core when hot, especially when you turn the engine off after a thrashing. There doesn't seem to be a good path for the air bubbles to make their way back to the radiator. Added to the fact the block isn't cooled directly and the only coolant path is out one small hole in the back of each head, it definitely isn't up to the task of cooling any more than stock power levels.

[sav man]

Looks like a have a small leak somewhere. But a good bleed fixed it for the moment. Just need to trace the leak now

[Thejackal98]

Hey guys. Got an m35 which randomly overheat after like stop start driving. Pushes coolant out of reservoir and I open up bleed valve and air pisses out

Replaced rad, rad cap, thermostat and clutch fan still heats up.

Pressure test is fine. Nil gasket issues

Any advice I'm loosing my marbles

[Ben C34]

Bleed it properly? Air is meant to come out. Keep doing it untill coolant comes out.

Edited October 5, 2014 by Ben C34

[Thejackal98]

Hey Ben. Ye I have bled it for like an hour . Filling it up through bleed valve with heater on. Any other thoughts.

Maybe bleed it longer or lets it sit their idling for hours ?

Thanks mate

[scotty nm35]

Heater off. Fill the rear bleed point with water.

Repeat when cold.

Or buy my coolant mod.

[Daleo]

Heater off. Fill the rear bleed point with water.

Repeat when cold.

Or buy my coolant mod.

^^^^This. So much this.