[AVR]

Hey folks

Been troubled with a peculiar issue which most mechanics have been unable to diagnose properly

Issue:
Endy drives very well till 90 where it shifts to the 5th gear and continues cruising smoothly till about 100-105 where rpm is in 2-2.5k range and engine temperature is normal. Now beyond that you keep pressing the throttle but it doesnt go any faster but if you keep the throttle pressed the engine eventually starts overheating (3/4th of gauge). Once overheated it also cools down when you step off the gas and let it drive in the 80-95 range.

- There are no vibrations or jerks all throughout
- It does not give jerks in shifting
- It does not feel constrained in power reaching till the 100-105 range
- Spirited trials and sprints with full revs also cause the engine to overheat (3/4th of gauge) but it cools down if you let it cruise for sometime


What has been checked
- Fuel pump and injectors are ok. Entire fuel line has been checked
- Gearbox is checked and replaced
- Wheels are upsized to 17inch Fortuner size which may confuse the AT TCM
- Air flow has been checked and filters replaced
- Cooling system has been checked and radiator replaced
- There are auxiliary Hellas 3003 that may impact the airflow but doubt so.

Me and my mechanics have been scratching our heads for a solution so thought I'll throw it at you guys if you want to rack your brains too.

Happy to hear from you guys!

Cheers,
Adi

[vigsom]

My thoughts here

1. The coolant system looks to be limiting - increase engine rpm which means increase in heat load on the cooling system and temp goes up. This could be due to a simple faulty radiator cap - please check.

2. Because the coolant system is limiting, the AT fluid isn't getting cooled enough. This might be limiting transmission load.

[varunsangal]

If overheating it is usually the cooling system acting up. Typically with the symptoms you describe, it is the radiator clogged with dust that acts up. Given you have already replaced the radiator, would suggest checking that the radiator fan is working optimally.

Also, has the coolant itself been changed? You may want to use a different grade of coolant.

[Jaggu]

How is the health of the engine? Have you done a compression check? is there any oil or coolant consumption from the engine. How much has it run?

To check if it is the airflow, you can temporarily remove the aux lights and test. Also does this model comes with any sort of electrical fan for cooling? If so check if it is working for engine and well as AC parameters. The radiator shroud around the fan is in tact?

The coolant regulator valve for cold, hope that is working as it should?

Last but not least, hope the temperature has been measured using another temperature gauge also? and is not an electrical issue in the meter or the circuit?

[AVR]

Originally Posted by vigsom

My thoughts here

1. The coolant system looks to be limiting - increase engine rpm which means increase in heat load on the cooling system and temp goes up. This could be due to a simple faulty radiator cap - please check.

2. Because the coolant system is limiting, the AT fluid isn't getting cooled enough. This might be limiting transmission load.

The radiator is new since the earlier one got clogged and the engine overheated back in December. Now that time, the person driving was generally pressing on the gas but the car wouldn't go faster than 90-ish and hence it had a breakdown. With the new radiator am assuming these issues are addressed. Will check about the cap though.

Originally Posted by varunsangal

If overheating it is usually the cooling system acting up. Typically with the symptoms you describe, it is the radiator clogged with dust that acts up. Given you have already replaced the radiator, would suggest checking that the radiator fan is working optimally.

Also, has the coolant itself been changed? You may want to use a different grade of coolant.

Honestly use standard coolants and have not explored different grades. The fans work alright.

Originally Posted by Jaggu

How is the health of the engine? Have you done a compression check? is there any oil or coolant consumption from the engine. How much has it run?
The coolant regulator valve for cold, hope that is working as it should?
Last but not least, hope the temperature has been measured using another temperature gauge also? and is not an electrical issue in the meter or the circuit?

Engine has done 48k and is in good shape. It behaves very nicely till the 100ish range without any constraints. There is no oil or coolant consumption as such.
Will check about the valve.
We used direct ECM readings and cross-verified with the gauge which is accurate in that sense.

This has been more baffling in diagnosis than anything I've broken on my 540 so far!

[Jaggu]

Originally Posted by AVR

The radiator is new since the earlier one got clogged and the engine overheated back in December.

Do get the head gasket ruled out also, if you have not done it till now.

[narayanang76]

Have you checked Mass Airflow Sensor, Turbo Modulator, turbo hoses and Intercooler? Also replace your fuel filter (diesel filter) and try that also.

If not already done, get an OBD scan done as well.

[dhanushs]

Since most of the checks have already been done, I'd suggest lifting the car up and seeing if any wheels are jammed. Apart from the engine is there any other part abnormally heating up?

Its a big diesel, any minor obstruction like slightly jammed brakes will not be felt in slower speeds, but, it's at higher speeds where 'power' is required, it shows up.

If wheels arent jammed, then check the differentials, then the gearbox. To me, (Since most other checks are done) it looks like the engine is working harder than it should be. btw, hows the FE?

[gkveda]

Was this issue there when you had stock wheels? Did it show up after you changed to Fortuner sized wheels?

Suggest you switch back to Stock wheels and check if the problem persists. ECU may have interpreted the speed variation due to different Tire size vs engine RPM, misinterpret the difference and some silly logic and finally, stop revving

My solution has no proof, but, just thinking this may be a cause. checking wont harm anyway.

[purohitanuj]

What is the model number of AT? If it is 6R, then please check the TC lock mechanism. I would assume TC is unable to lock which is required to attain higher speeds which "the fluid" cannot deal with.
Cooling would not an issue on highway as majority time is spent with lock ON (unless the accelerator is abused).

[AVR]

Originally Posted by Jaggu

Do get the head gasket ruled out also, if you have not done it till now.

Checked and no issue.

Originally Posted by narayanang76

Have you checked Mass Airflow Sensor, Turbo Modulator, turbo hoses and Intercooler? Also replace your fuel filter (diesel filter) and try that also.

If not already done, get an OBD scan done as well.

All sensors have been cleaned and fitted back. No errors being thrown on a scan both at company and outside garages.

Originally Posted by dhanushs

Since most of the checks have already been done, I'd suggest lifting the car up and seeing if any wheels are jammed. Apart from the engine is there any other part abnormally heating up?

Its a big diesel, any minor obstruction like slightly jammed brakes will not be felt in slower speeds, but, it's at higher speeds where 'power' is required, it shows up.

If wheels arent jammed, then check the differentials, then the gearbox. To me, (Since most other checks are done) it looks like the engine is working harder than it should be. btw, hows the FE?

Wheels and brakes were serviced and all was found ok. rolls nicely without any resistance (learnt to gauge it thanks to the Jeep)

The engine doesnt sound strained if driven comfortably. FE is horrible in general around 7.5 kmpl

Originally Posted by gkveda

Was this issue there when you had stock wheels? Did it show up after you changed to Fortuner sized wheels?

My solution has no proof, but, just thinking this may be a cause. checking wont harm anyway.

Just back from the garage and this is what we are trying since a Ford guy also called up and mentioned that we should try this. Maybe some flat spot in the shifting logic happening due to taller tyres though I feel it shouldnt matter. FYI Stock size is 29.5 and currently at 31.5 inches.

Originally Posted by purohitanuj

What is the model number of AT? .

This is the 5r55W and it goes into 5th gear around 85. Will read about the TC lock issue if applicable

The mechanic is totally zapped too. The question mark on his face was almost worth a laugh but since eventually, I am at the receiving end of this hassle I let it go.

Even thinking of removing snorkel and aux lights and making the front stock and seeing if it helps.

Quite often such problems have very trivial solutions. When you find them. The search continues...

Adi

[dhanushs]

Originally Posted by AVR

Wheels and brakes were serviced and all was found ok. rolls nicely without any resistance (learnt to gauge it thanks to the Jeep)

Well, if you have a 4x4, worth checking if you have drivetrain wind up. Symptoms will be very similar.

Try removing both the front flanges and recreate the same circumstances. Will rule out differentials acting up too.

[Mortis]

Assuming your radiator fan is a dual speed one can you check if it's going into high speed mode as temp rises ?

Also is there any difference in the high speed behaviour that you are reporting with the AC Off Vs On ? Ideally it should perform a bit better with the AC off. Also has the intercooler been checked and cleaned both externally and internally ?

[.anshuman]

Did you get the Fan clutch checked? If the fan clutch has gone bust, the fan will appear to be spinning but won't provide sufficient cooling.

The ECU will start cutting down on power if the coolant temperature goes beyond 104-5 c. At higher temp, it will cut down power more aggressively.

[AVR]

So there has been some progress. Apparently there is an issue with the vacuum pipe in the turbo and it's modulation. Yesterday a TD with the pipe disconnected felt smoother and more powerful. Will be going Monday to check on it.
Will keep you guys posted.