overheating f75

[nid]

Hello all,

I have an f75 2.8td (intercooled) which is overheating on a hot day when I am going fast (above 3lbs/ square inch turbo boost). It is fine at idle or on cold days. I have replaced the rad, thermostat but the problem remains.

Any idea what I should do next?

Yours
NID

[lay80n]

Have you checked ya cooling system for leaks, pressure tested it. Check ya air cleaner, diesels overheat when run rich, or timing advanced (as well as the obvious cooling system faults like leaks etc.). If your air cleaner is blocked then less air in allowed in, so runs rich. Does you rig blow and smoke.

Layto....

[flynn]

how hot is it getting?? some rockys run hot for some reason....

[Patchy]

have you cheched your fan? i belive they are a viscous hub, belt driven fan? you should be able to spin it by hand with some resistance if its almost impossible to turn by hand or it turns too easily its ....

alot of people over look viscous hub fans but because you have done everything else i would be looking at that.

also if you have a/c have a look at the condensor fins could be blocked and preventing air flow

[HotFourOk]

when I am going fast

This lets you know its probably not the fan causing the problems... unless its spinning backwards

The fan has negligible cooling effect when travelling at faster speeds.

[Patchy]

when I am going fast

This lets you know its probably not the fan causing the problems... unless its spinning backwards

The fan has negligible cooling effect when travelling at faster speeds.

Wrong if the fan is stuck (therefor going the speed of the engine all the time) then the fan will be causing a "back log effect" as such preventing full air flow through the cooling system, at high speed with high revs.

this happens because air goes to flow through the cooling system, gets blown back through the cooling system the other way by the fan. (much like if you were to tryblow in to the fan at home)

i think that makes sence.

[HotFourOk]

if the fan is stuck (therefor going the speed of the engine all the time)

If the fan is going the same speed as the engine.... at higher revs, the fan will work well So cooling would be good. I dont know what you're trying to say here.

this happens because air goes to flow through the cooling system, gets blown back through the cooling system the other way by the fan. (much like if you were to tryblow in to the fan at home)

This is nothing the same... If you blow into your fan at home, the air is travelling in the opposite direction... The engine fan will never cause this.

How can the air get blown back through the cooling system?? The fan still pulls air through the radiator no matter what... Its not going in the reverse direction

If the fan is travelling at a less than desired speed, it will create some turbulence with the airflow though the radiator, and this may cause ill effects... I was making the point that if the fan was not operating at all.

If the fan ceased to operate, it would make no difference when the vehicle is going fast (And dont try to tell me this bit isn't right).

But the fan working albeit not correctly may do so.

[Patchy]

well in thery your saying there would be no need for viscous hub and that belt driven fans shoud just go back to prior 1980's, where the fan was bolted straight to the water pump.

and yes your right the fan shouldnt make any differenceat speed if it wasnt working at all.
p.s: my exampple wasent the best. but hopfully this description helps slightly better

the idea ofa viscous hub is adust the amount of slip the fan has in relation to engine speed and surrounding air temp. what i am trying to say is yes although fans blands are angeled to draw air in and through the fan. that the fan is only bennifical to a certin speed. anything above this speed the fan becomes restrictive to air flow. e.g: the fan moves so fast it begins the make a sort of barrier for air forced through the radiator to try and pass, wich causes a "back log" of air passing through due to the ram effect of speed

[nid]

well, the fan is fine. And the engine goes into the red if I keep going for long enough. It hasn't blown up yet - but I am worried that it is going to.

As I say, this happens on a hot day (~30 deg C) going at only 3lbs boost - thats about 85Km/h.....

Could it be something to do with the water pump? How would I diagnose that?

Thanks for your input.

NID

[jav]

had the same problem with my 92 rocky, only thing that made a difference was when i put some 10mm spacers between the bonnet and hinges, looks ugly but it did help.

[nid]

er..... this IS a 92 rocky. any more ideas?

[HotFourOk]

Have you checked ya cooling system for leaks, pressure tested it. Check ya air cleaner, diesels overheat when run rich, or timing advanced (as well as the obvious cooling system faults like leaks etc.). If your air cleaner is blocked then less air in allowed in, so runs rich. Does you rig blow and smoke.

Have you done any of these?

[nid]

all of those are fine!

[HotFourOk]

Well it pretty much has to be the water pump. Everything else has been covered..

You could flush out your block also, to rule out any blockages.

[nid]

I will flush profusely.

Is there anyway I can test the water pump so I positively know that I need a new one - rather than it simply being 'by elimination'?

Thanks for all your input

NID

[HotFourOk]

not really... check for any sign of wear, or take it off and see if the blades are damaged... but by that stage you can replace it anyway... lol

[murcod]

Is there anyway I can test the water pump so I positively know that I need a new one - rather than it simply being 'by elimination'?

You should be able to see the coolant flow start in the radiator once the thermostat opens & it should vary with engine speed.

[Patchy]

you could always try put a new thermostat in, one that opens sooner just a thought, not sure it will help tho