Thread: Over heating 4x4

putting the air con on should have a detrimental effect on the cooling capacity of your vehicle, I dont think your auto fans are kicking in, check fuses and maybe connections, by turning the air con on you are overriding the cooling fans auto mechanism and that is what is cooling your engine!

Yea I think the fan is ok it's running when the car is hot, but the radiator hose is not having much water going through.

hmmm! have you a friendly radiator specialist in your area or someone who is mechanically minded just o give you some idea of the problem, not much water could be water pump or thermostat sticking or even blocked radiator, if you could get the system checked may be the way to go then work out what it is going to cost you! can you follow the top radiator hose back to the head, this is where the thermostat should be! maybe buy a new one and another gasket and replace it then go from there, dont lose the coolant it is expensive stuff to replace, catch it in a bucket and return it when repairs to the thermo are complete, do you know how to replace the coolant in a hot engine without cracking the head

If the motor has overheated the coolant will be useless anyway so best put new stuff in.

As Dave has said go to a radiator place and have the system checked.

the motor did not cook, just went to top end of the scale then it cooled down.

i just dont want the mechanic to hit me up for new water pump when it could just be themosate or some thing simple.

my plan is to take it to our mechanic who does our merc's and get him to have a look and try to suss out.

the heads are ok i check the oil and its not milky.

Originally Posted by Gaza

the motor did not cook, just went to top end of the scale then it cooled down.

i just dont want the mechanic to hit me up for new water pump when it could just be themosate or some thing simple.

my plan is to take it to our mechanic who does our merc's and get him to have a look and try to suss out.

the heads are ok i check the oil and its not milky.

Sounds like a plan.

the trouble with finding a problem is exactly that, finding it, you could replace the thermo and it may not be that $$$$$ replace the pump and it may not be that $$$$ replace the thermo fans and it may not be that $$$ I find it is often cheaper to take it to a good reliable mechanic and have it checked and get it fixed right the first time, even though I do a lot of my own work I still get caught

just last weekend I went to start my camper for it's weekly run, motor was slow to turn then just a few clicks audible from the starter, ah!!! flat battery says I, possibly down on fluid, went to check it, lids a bit tight and no obvious sign to get to it, out with tools, still no go, Dave get angry now, must check fluid, cut top off battery, oh oh fluid fine, took battery to RAA to get checked, HMMmm!! battery good, but now destroyed by Dave trying to check fluid level, new battery, WHAT!!!!!! $160 good god!!!! oh well give me one, place battery back in camper, still only got clicks then nothing, HMMmmm! starter motor knackered, take to auto repair, $60 for new brushes! total cost of anger and incorrect diagnosis $220, cost if taken to auto electrician in first place, $80, Bugga!!!!!

I live, I learn!

The thermostat will be at the point where the top radiator hose connects to the engine block.

The thermostat housing will typically be aluminium, and may have one or more connections for temperature sensors. It may be under one of those "thare be daemons under heayar" plastic covers so beloved of car makers these days.

Typically they are held on by two nuts or bolts, and there is either a gasket or an O-ring seal that'll need replacement when you take the housing off.

To test the thermostat, hang it in a pan of water on the stove and heat the water. You should see the thermostat open as the water warms up (typically they are fully open between about 70-90 degrees C...sometimes the open temperature is stamped on them).

A replacement thermostat is usually under $20.

However...

If it is overheating until you put the air-cond on, that suggests that the problem is that the main fan isn't switching on (assuming you are not doing highway speeds...at speed, airflow through the radiator should be quite sufficient for cooling) if it is an electric fan, or, if it is a fan driven by a pulley from the engine, then the viscous coupling on the fan body may be knackered. Here's a possible way of testing if it is - http://www.landsharkoz.com/tt/ttvfc.htm - you may be able to come up with a similar sort of locking plate, or the service manual may have the 'approved' testing technique for the fan.

I agree that the issue is almost certainly to be the main fan not working. All aircons switch on an electric fan ( either main or auxilliary depending on your setup) and that is the only thing it does that will assist with the cooling. This means that prior to turning on the aircon, there is no air being forced through the radiator, other than by the vehicle's forward movement.

Time to replace or repair the main fan unit - I think yours should be a viscous coupled job. If it does need replacing, I would do a search for Isuzu spare parts and try to source one online, if local prices are not satisfactory.

Originally Posted by TP1

I agree that the issue is almost certainly to be the main fan not working. All aircons switch on an electric fan ( either main or auxilliary depending on your setup) and that is the only thing it does that will assist with the cooling. This means that prior to turning on the aircon, there is no air being forced through the radiator, other than by the vehicle's forward movement.

Time to replace or repair the main fan unit - I think yours should be a viscous coupled job. If it does need replacing, I would do a search for Isuzu spare parts and try to source one online, if local prices are not satisfactory.

feel free to correct me if i am wrong, is there a fan behind the grill in front of the radiator as well as the fan that runs off the engine.

There will usually be an electric fan (or two) in front of the air conditioning heat exchange radiator, which will be just behind the grill. This is specifically for the air conditioning and is switched by it.

The engine radiator will be behind the air cond. radiator, and the usual place for the engine radiator fan is in the engine bay; its quite atypical to find an engine radiator (electric) fan in front of the radiator.

Someone will of course now chime in and say that an obscure model of British Leyand/Tata/Yugo in fact had an engine coupled fan mounted in front of the radiator, powered by an innovative magnetic coupling that never worked/offset belts and gears/shaft penetrating the radiator core, just to prove me wrong.

Originally Posted by Gaza

feel free to correct me if i am wrong, is there a fan behind the grill in front of the radiator as well as the fan that runs off the engine.

There should be a fan in front of the radiator behind the grill as Master Splinter mentioned. This one is clearly working OK.

The main fan unit will probably be a viscous coupled drive unit. These are designed to rev slower when the engine is cold and as the engine heats up, the internal mechanism ( inside the fan hub) operates to increase the fan speed for any given RPM. So even if your fan belt is OK, the drive mechanism inside the hub of the fan unit may be faulty and not engaging properly, which would explain why it is not spinning sufficiently to cool the engine.

This is all theory since we cant actually see your car but there doesn't seem to be another plausible explanation on the info available.

Alloy heads can corrode and develop porosity. It is not uncommon for the head to develop a leak between the water jacket and the combustion chambers. In this case combustion gasses overpressurise the cooling system causing it to loose coolant through the pressure cap/overflow system. With this type of leak, the coolant and oil do not mix, so there is little chance of sending oil milky. This can only occur with significant running with a leak between the water jacket and oil system, typically from a blown head gasket leaving a bridge between oil galleries and waterjacket, or leaky cylinder seals on a wet sleeve engine.

You suggest that there is not a lot of coolant flowing through the top hose, suggesting that the coolant is low, or something is impeding its flow. Has the coolant level dropped recently, suggesting overpressurisation and venting?

If not, does the upper hose feel firm (i.e. feel like it is under pressure) or soft, possibly gurgling if squeezed. If under pressure, then it indictes that the pump and thermostat are working allowing water to the hose but the flow is impeded elsewhere, typically in the radiator.

If there is little or no pressure at the hose and it can be easily squeezed, this indicates that there is limited flow, suggesting the pump, thermostat or some form of internal collapse within the engine. As an example, I had a similar problem with a Peugeot 504 some years ago which was ultimately traced to a welsh plug behind the water pump coming loose allowing water to renter the pump after travelling less than 6 inches after exiting it.

update,

all fixed ended up changing themosate and had raditor flushed.