Overheating issue-advice.

[Kappy]

Here's one for the mechanical gurus.

Returning home recently, I experience a couple of episodes where the bus apparently overheated,

Generally bus sits on around 90C then out of the blue hits around 100 and needle flickers.

2 occasions the Temp buzzer came on.

Stopped checked everything no normal obvious signs of overheating. Drove for hundreds of K's with no issues at all

The flickering on temp gauge doesn't appear to be consistent with poor ground all that was sorted a little while ago by a guru Bus Auto sparky.

So before I start pulling all and sundry apart, will end up pulling out radiator and have it flushed, but don't think that is problem.

Can temp sensor maybe faulty, or could thermostat be playing up.

Could a faulty sensor trigger buzzer to activate,

I travelled some pretty hilly terrain with no issues. Only occurred on flat cruising.

Please keep it simple LOL

[BernieQ2]

Morning Kappy, could be a simple as needing a new radiator cap??
Bernie .

[Busman]

Sounds like a faulty sensor to me

[supersparky]

Is it really getting hot and /or using water? If yes then start with checking the cap as Bernie said, or maybe the hoses. But if it is no, then it may be a wiring problem. Is the buzzer a low water or an overheat alarm?

[jon_d]

Kappy,

Generally bus sits on around 90C then out of the blue hits around 100 and needle flickers.

2 occasions the Temp buzzer came on.

These are two important points. Your descriptions are always helpful and excellent.


Can you try and work out if the buzzer and gauge are using separate wires and senders? The buzzer will have a temperature switch, and the sender will have a temperature sensor.

The reason for asking this first is because if there are 2 separate circuits then the warnings are independent of each other. ie; it's indicating that you have a real issue and not an electrical issue.



Things to look for;

Old hoses that are soft. Especially the big hoses that might be collapsing under suction. The suction hose has a wire spring inside to stop it collapsing. They can rust away.
Sticky thermostat - just replace it.
Old radiator cap - just replace it.

It could be the clutch in the fan is getting old and not engaging at the right temperature.. (remember, you have a rear engine.) I went to look at the fan video you posted but it's been removed.

hope this helps. jd

[native pepper]

Kappy, the standard engine temperature gauges don't represent the temperature of the engine in real time, they gauge the temperature of the coolant, not the real engine temperature. Then there is the engine temp gauges which attach to the head or block, which gives metal temps.

Finally there's the only real way of establishing engine temps and that's measuring the exhaust gas temperature at the outlet manifold and any engine that has a turbo should have an EGT gauge. An EGT gauge will tell you exactly what temperature the engine is at in real time, so they fluctuate constantly and the art is driving your vehicle within certain temp parameters.

My bus has an Isuzu turbo engine and it has a water temp gauge, engine temp gauge and an EGT. The water temp gauge lags a long way behind engine temp gauge and even more behind the EGT, which tells me what the actual cylinder temps are. I drive on the EGT and it has saved me a lot of money because big vehicle temps change dramatically, so I keep the EGT between 200deg and 450deg. It does change your driving techniques but you end up with better results and much longer engine life and peace of mind. Add a front mount inter cooler and most of your problems will be solved as inter cookers cut EGT temps a lot.

Less than 2000klms ago I rebuilt the engine in my series 80 cruiser after 500000klms and the change in EGT has been amazing. Before the car temp gauge rarely moved, but the EGT ran between 350 and 650deg, which is why I decided to rebuild. Now the EGT sits at less than 200deg and under acceleration up big hills, it can be controlled with little loss of power to stay below 450deg. Of course the inter cooler helps a lot as does the upgraded turbo, but an EGT will give you the right temp of your engine when you need to know and not after a lag or some form of fault.

I'd drain and flush the cooling system, some types of coolant when they get old can become a bit cloggy within the system and your problem may be that or a faulty thermostat, sensor or the indication that a fault is developing within the engine and the only way you can tell is with an EGT. It could be the water pump is beginning to fail, as they are pressed on to their drive shafts and when they get old or after lots of high temp driving, they can tend to cause cavitation in the cooling system as the water pump begins to slip on its shaft. Which means air pockets moving around the engine, expanding and contracting, causing loss of cooling to some parts at times and that would give you the temp changes you are seeing.

An EGT is easy to fit and it takes just a few minutes, as most exhausts especially turbos come with a place to fit the EGT and you can get them off ebay for less than $50, my new one cost $37 delivered and I carry a spare in the bus. If not you can buy after market dump pipes with EGT connection points in them, or drill and tap a hole yourself.

If it's a developing fault, could be a bearing becoming dry at times, or some other internal part not getting coolant/ lubrication, or beginning fail.

[jon_d]

NP,

Do you have a link to the $37 ebay EGT gauge?

[native pepper]

Here you go Jon, this one registers in centigrade, many on ebay are in Fahrenheit.

https://www.ebay.com.au/itm/52MM-Car-12 ... 2749.l2649

[Kappy]

The buzzer is a multi use., covers air, clutch and other I guess.

The wiring was all sorted by Bus sparky, he rebuilt aspects of the dash gauges that shorted out due to poor grounds, that too he sorted. making 3 new grounds to the dash, body chassis and engine each.

I have no idea how the wiring works, buzzer and the temp light activate at the same time.

The fan operates at what appears to be all speeds, doesn't seem to have a clutch mechanism.

The 1st time the buzzer /light activated I stopped, idle for a few minutes, then shut down, on checking coolant in overflow tank observed to be full/overfull, if that makes sense.

On restarting after about15 minutes, temp gauge displayed approx 75 degrees.

Think I heard or read somewhere that there are different temp, caps and thermostats????

[jon_d]

"The 1st time the buzzer /light activated I stopped, idle for a few minutes, then shut down, on checking coolant in overflow tank observed to be full/overfull, if that makes sense"

Expansion into the tank is expected. As the water heats up, it expands and builds pressure. The cap releases and the water flows into the expansion tank. If the cap is old, or wrong pressure rating, the cap can be releasing to early and causing problems. (boiling or pump cavitation.)

When the motor cools down, a vacuum is created and sucks the water from the tank back into the radiator.


With out knowing/seeing the bus, I'd replace the bottom radiator hose (suction side of the pump) and the radiator cap (with the correct pressure rating) as a precaution and first step.

Next would be the radiator flush/recore and pump inspection/replacement.