VS 5 litre overheating troubles...

[Phreddy]

G'day there guys.

My VSII V-8 is getting too hot, but it's a bit of a wierd one....

It only seems to overheat when on the freeway, or during a sustained higher speed run for 20+ minutes or so. Putting around in traffic doesn't bother it too much. I've checked the obvious things, replaced the thermostat (cheap enough), and was about to do the water pump but after I'd removed it the one on the engine was fine. Full reverse flush of the block, radiator, and heater core, then refilled with brand new Nulon coolant at the correct dilution.

The radiator is a rconditioned unit, installed by Natrad about three months ago. (before I got the car) Therefore I'm not suspecting the rad, even though I suppose the symptom points to a partial blockage...(?)
(has anyone else experienced trouble with Natrad's work?? I though a reco radiator was pretty straightforward)

It's still carrying hte standard "clutch" fan - one thing I've noticed is that even when the engine is hot, there's not a lot of resistance when turning the fan by hand (with the engine stopped of course!) - I though these were supposed to "tighten up" a bit when they get warm.... ????

Question - does the fan clutch play up? Is it the sort of thing that can be suspect in a situation like this??? I'm toying with the idea of pulling the engine fan off anyway, and fitting a thermo electric fan...

Ummm - one other thing that I might mention.... I've fitted a set of headers (to replace the iron manifolds), and the fella I bought them off said that they shouldn't have a manifold gasket fitted.... I don't disbelieve him, but is that info incorrect?? (I wonder of a gasket provides some level of heat insulation, and if the headers are bolted straight up the heat from these is making the heads hotter - therefore heating the coolant more than it should be...) Dunno if that's logical but I'm running out of ideas.

Should I check the base timimg? (if it's too advanced, that would make it run hot, right?) Is it possible that there IS something wrong with the water pump, despit that it looks fine? (it's the type that has the cast iron impeller, not the cheaper spot-welded type) The bearing seems fine, and there's very little corrosion....

Anyhow, input welcomed.... I have to drive to Melbourne in a little over a week, will be a slow trip if she's always near boiling though...

Thanks guys! :bang:

 

[VrWagz1]

The only thing i can think of on for over heating on the freeway is the little peice of black plastic strip at the bottom of the radiator that directs air up into it might be missing. For some reason air dsnt really flow that well through the raditor while driving and that plastic thing helps direct the air up and creates some sort of flow
I would not suspect the clutch fan as that is the idea of a clutch fan, It stops spinning once your revs are up and you are moving as your forward motion moves the air through the radiator. Hope thats it anywayz. I could be way off yet though

 

[hako]

As above with the clutch fan - at highway speeds the air flowing thru the radiator from the movement of the car far exceeds the air moved by the fan. The manifolds should be OK without a gasket if designed that way. Maybe it's the temp gauge playing up or maybe it's quite normal - I know if I cruise at 125kph the gauge will be about 1/8 hotter on the gauge than at 100kphwhich is to be expected as the engine is working harder and needs to get rid of extra heat.

 

[delcowizzid]

excessive temp at cruising speeds can also be a damaged head gasket but ide be checking base timing first and also that theres no air trapped in the cooling system

 

[Phreddy]

Thanks for the input guys.... Yeah, I wasn't really suspecting the fan....

VRWagz - thanks for thap tip - I'll have a squiz at that.... And check the timing I guess.... Bloody hell, I hope it's not the gasket.... Bastard of a job....

Hako, understand your point, but it's a dramatic rise. The gauge gets up over 3/4, the engine temp warning chimes, and it does boil... Not violently, but enough... The crazy thing is that the trip I did to Brisbane a little over a month ago, it never missed a beat. Ran like a dream....

(by the way, I have looked for the symptoms of head gasket trouble - ie, water in oil / oil in water / bubbling in the radiator....)

Damn, need it to be right for this Melbourne trip.... :unsure:

 

[Phreddy]

Delcowiz - is there a process for bleeding trapped air from the cooling system? According to the Holden manual, there's no particular procedure... The radiator cap is the highest point in the system as far as I'm aware... I know there's a need to bleed the V6, but the V8??

(if there's a procedure, please enlighten me!)

 

[delcowizzid]

run it with the radiator cap off and the heater on hot untill the thermostat is hot enough to open and keep topping it up as required till its full and no air bubbles are seen appearing at the radiator filler neck

 

[VrWagz1]

phreddy, i done mine heaps an its very hard to actually get air trapped in the system on the 5ltrs. as you say the radiator cap is the highest point, but what delcowizz is good practice.

 

[hako]

How is the radiator cap - if it's not holding pressure it will boil however you say the hi temp warning comes on....bottom radiator hose collapsing at high revs and restricting flow?...why was the radiator replaced 3 months ago - probably due to overheating???....could the exhaust headers be somehow blocking the exhaust flow due poor manufacture....is the O2 sensor in the correct position on the exhaust....get a radiator shop to test your coolant for exhaust gas, this is a positive test.....

 

[Phreddy]

Thanks again fellas - DelcoWiz - thanks for the tip Mate, makes sense!

Hako - your suggestion is a good one too - reckon I might just do that. (coolant test...) It's possible that the bottom hose is collapsing I guess, wouldn't be terribly clostly to replace anyway.

Anyhow, here's hoping I guess. Cheerz!