2002 Prado TD Auto - Overheating whilst towing

Submitted: Tuesday, Aug 08, 2017 at 21:44
ThreadID: 135368 Views:4279 Replies:6 FollowUps:10
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Forgive this lengthy post

I occasionally (anywhere from 2-10 times per year) tow with my 2002 Prado TD Auto, now with 390K on the clock. Trailer is an enclosed dual axle box trailer carrying a small PA system, drum kit and other musical instruments so not particularly heavy all up, perhaps 500-600kg?
The journey is usually from Syd to Hunter Valley, about 200 ks each way with an overnight stop between each leg.

About 2 years ago she overheated whilst towing, no cause could be found. Coolant topped up and no further issues until our next towing trip where she boils again. This time I take it to mechanic who diagnoses a leaking water pump which is replaced. Next trip, same issue though soon after it's running rough as guts and the dreaded white smoke begins to appear. Back to mechanic, who diagnoses a cracked cylinder head. One big repair bill later for new head, radiator, hoses etc and we are underway again.

The next issue that rears it's head (and I'm not thinking this is related to anything but including it here so the history is complete) is the Diesel injector pump claps out. This gets replaced along with new injectors and she's running like a train again.

Another towing trip away soon follows and she once again overheats like crazy on both legs of the trip. Back to mechanic we go, no detectable damage to head after all the tests are performed, so everything gets checked, mechanic borrows a 3 tonne trailer and gives it a good thrash for an hour or two without drama. In the meantime I read somewhere else on this and other forums that towing in the Prado's overdrive 4th gear is not recommended and this can lead to overheating as the transmission can't cope and somehow (IIRC) dumps heat into the cooling system (feel free to enlighten me on how this is possible/impossible). So the next trip I make with the trailer, I leave it in 3rd with the Overdrive lockout switch engaged and everything goes well.

Happy days? Problem solved? Not so fast...Some rough idling on startup begins to make its presence felt, and then, a couple of weeks ago i make a trip up the blue mountains WITHOUT a trailer and she overheats once again, I put about 3 litres of water into the radiator and limp home, and since then, the rough idling at startup is getting worse and I'm losing about a litre or two of water per day. Mechanic is preparing me for another head calamity, blown head gasket at best, cracked head at worst. Have still yet to get it to him due to crazy work schedules, and I need a car to get to work to pay the bills that are soon to appear!

Seems that the most recent bout of overheating since replacing the head did the damage and even though it was undetected at the time, something has happened to make me lose water perhaps into the combustion chamber (hence the rough idling) and this caused me to overheat driving without the trailer, due to a simple lack of coolant (I regularly check the reservoir and this is ALWAYS full). BTW, the oil on the dipstick ISN'T milky but this could indicate an issue on the exhaust side of the head, correct?

1. Am I missing basic something that is causing me to overheat whilst towing? A few ppl tell me to replace the thermostat but wouldn't a faulty one cause me to overheat every time I drive, not just with the trailer? Pretty sure thermostat was replaced, as was radiator cap when the new head went in.
2. Was/is the towing of the trailer in overdrive a legitimate factor? Does this indicate a cactus transmission? Or will installing an inline transmission cooler save the day?

I'm very attached to the old girl, would hate to see her go, but I've spent about $13K on repairs over the last 18 mths and I'm still overheating, with possibly another $5-6K bill just around the corner. Can't afford to replace it just yet, but I don't want to put a new head on if I'm just going to overheat again the next time I tow the trailer.

Thanks for reading, any thoughts appreciated!!

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Reply By: RMD - Tuesday, Aug 08, 2017 at 22:19

Tuesday, Aug 08, 2017 at 22:19
No mention has been made about the viscous fan clutch which should drive the fan to provide additional cooling air flow through the radiator. At those km's it is almost certainly stuffed and not doing it's job and probably requires checking. Any decent mechanic should check that operation first up with a cooling problem.

The auto will produce heaps of heat into the radiator by dumping it's developed heat into the radiator water. If towing, an auto trans fluid cooler is a great idea and have it placed in the exit line from the auto, so maximum heat is given to passing air and minimum to the radiator water.
The radiator water will be a little hotter anyway if towing, and the air drag of the trailer may be making the engine work much harder than simply the weight of the trailer indicates. All sources of resistance have to be factored into the work done by the engine and the auto. Both of these produce heat which must be dissipated by the radiator.

The thermostat should be replaced when engine work is done AND it's operation to "fully open" should be checked, even the new thermostat must be checked.
The amount of water getting through a partially opening thermostat MAY give enough flow for normal driving and heat dissipation. BUT, when towing and engine AND auto heat have to be got rid of, the auto can tip the balance and the water entering the engine from the bottom of the radiator (normally cool) will be quite hot and have no abilty to absorb much heat from the engine,. Therefore the engine overheats.
It appears the mechanic isn't checking enough of the vitals to find the problem.

Driving in overdrive, if it stays in overdrive, loads the engine more.= more heat into water.
If under load and the autos torque converter is in slip mode, the engine is relieved a little bit but the auto fluid temp rises markedly and WILL be far hotter than the boiling point of water in the radiator. That still makes the radiator too hot.

The radiator itself may be blocked to some degree and sufficient water thoughput is OK for normal driving but when the thermostat opens to increase cooling water flow rate, the radiator may be the restrictive item. Again, a decent mechanic SHOULD be able to diagnose and rectify the issue First time around.
AnswerID: 612949

Follow Up By: RichieK - Tuesday, Aug 08, 2017 at 22:32

Tuesday, Aug 08, 2017 at 22:32
Thanks for some great info!
I did forget to mention that the viscous fan was replaced at the most recent trip to the mechanic, we didnt overheat the next time i towed, that was when i kept it in 3rd instead of OD..but seems that the damage was already done.

I'll double check what happened with the thermostat when i talk to him later in the week. Maybe get it tested/replaced.

radiator shouldn't be restrictive at any of the overheating episodes post radiator replacement 20K ago,,same time as head... could it be already crudded up again?

FollowupID: 883302

Follow Up By: Bushranger1 - Wednesday, Aug 09, 2017 at 07:06

Wednesday, Aug 09, 2017 at 07:06
G'day Richard,
If the radiator is blocked again then the mechanic is not using the correct coolant concentration or just plain water.
As you have found out the cooling system is critical to modern vehicles & just one overheating episode causes significant damage to the engine. Many early engine failures are caused by poor cooling system maintenance.
I keep my vehicles a long time & the cooling system in the Hilux I just sold with 400,000 odd km's was still like new because I always pay close attention to keeping the coolant changed regularly.
Certainly as advised above the Auto transmission can add significant heat load to the vehicle radiator so get this looked at too.

FollowupID: 883303

Reply By: swampy - Wednesday, Aug 09, 2017 at 07:09

Wednesday, Aug 09, 2017 at 07:09
Thermostat yes u can check it , but if it was not the cause they can fail from being over heated themselves anyway .
ALWAYS CHANGE either Toyota or Tridon brand
Viscous fan assembly
Fan blades cracked ?
Viscous hub [ at high km just replace it ] Dayco or Genuine Toyota
Water pump remove and inspect
Serious look at all hoses to be replaced at high km , perished /hard /crunchy
Head removed ALWAYS CRACK TEST new head bolts as needed
Always run a VERY LARGE trans cooler if towing as well as the factory cooler
Always have radiator cleaned out at rad shop [ tanks removed resealed and core rodded out ]
Flush engine block and heater ccore out to remove any corrosion debris
Replace radiator cap
AnswerID: 612950

Reply By: Keir & Marg - Wednesday, Aug 09, 2017 at 10:10

Wednesday, Aug 09, 2017 at 10:10
Not sure how many km's on the car but the Prado clutch packs in the auto box are susceptible to slipping when towing. If the clutch pack is slipping, the auto transmission oil will be burnt and black, and you will be getting excessive heat dumping into the radiator via the OEM transmission oil cooler which will then cause the overheating. At the very least I would suggest taking the vehicle to a decent auto transmission place to have the box checked out.
AnswerID: 612951

Follow Up By: Les - PK Ranger - Wednesday, Aug 09, 2017 at 11:28

Wednesday, Aug 09, 2017 at 11:28
"now with 390K on the clock" and that is well high enough for such issues to start coming out more and more often.
Unfortunately the OP pointed out they aren't in a position to upgrade at the momnet, but then repair$ can be so high in cost it is really can be better to finance and get something more reliable in the long run.
FollowupID: 883308

Follow Up By: Keir & Marg - Wednesday, Aug 09, 2017 at 12:38

Wednesday, Aug 09, 2017 at 12:38
Spot on Les. You get to the point where, despite the "investment" in extras in the car, it reaches a point where it just doesn't make economic sense to keep pouring dollars into an increasingly unreliable vehicle which has little residual value due to age & mileage.
FollowupID: 883310

Follow Up By: eaglefree - Wednesday, Aug 09, 2017 at 14:43

Wednesday, Aug 09, 2017 at 14:43
I had a radiator cleaned twice. Those days it was dismantled and the cores cleaned by pushing a rod down them.

Still overheated particularly when towing. Bought a new radiator and the car never overheated ever again.

The rough idle at start up could be a separate issue maybe injector or intake leak. Proper diagnosis is crutial. Find a prado guru imo.
FollowupID: 883311

Follow Up By: Les - PK Ranger - Wednesday, Aug 09, 2017 at 14:56

Wednesday, Aug 09, 2017 at 14:56
Yes, maybe it's time to get it tidied up again, make it as reliable as your wallet and conscience will allow for sale, and make an upgrade happen.
Sometimes it's just not worth holding onto a vehicle any longer.
FollowupID: 883312

Follow Up By: RMD - Wednesday, Aug 09, 2017 at 16:47

Wednesday, Aug 09, 2017 at 16:47
It is a Turbo Diesel. therefore an intake leak is hardly likely. are you thinking petrol????
FollowupID: 883313

Reply By: Shaker - Wednesday, Aug 09, 2017 at 17:56

Wednesday, Aug 09, 2017 at 17:56
Have you asked the same question at PradoPoint?
There is a wealth of Prado knowledge there!

AnswerID: 612960

Follow Up By: RichieK - Thursday, Aug 10, 2017 at 16:45

Thursday, Aug 10, 2017 at 16:45
Hi Shaker, yes i posted there first to get Prado specific replies, then posted here for more generic thoughts.. Both forums have been incredibly helpful.
FollowupID: 883330

Reply By: Member - Roachie - Wednesday, Aug 09, 2017 at 18:29

Wednesday, Aug 09, 2017 at 18:29
If you plan on keeping the vehicle, I suggest fitting a couple of items.....

1). EGT Gauge. Drive according to this and you'll be doing your engine a favour.

2). Engine Saver Low Water Alarm. http://www.enginesaver.com.au/ This item will alert you AS SOON as there is no coolant present in the top of the cooling system.

The fact that you mentioned at one stage in your post, that there is always plenty of coolant in the expansion tank provides me with a significant clue......

If you understand the principles of how a modern cooling system functions, you will know that it is a pressurised, sealed system. When the coolant in the engine/radiator heats up to a pre-determined temperature (governed by the "NUMBER" of the radiator cap), the radiator cap will allow excess coolant to move out of the sealed system, into the expansion tank.

Now....the tricky bit occurs when the engine cools back down.... The rubber hose from the expansion tank to the radiator MUST be a perfect seal. If not, the radiator, as it cools, will suck air back in rather than excess coolant.

This doesn't just occur when the engine is switched off etc.

Say, for example, the radiator cap is one that has a 113 degree opening spring. You drive up a hill and the coolant temp exceeds 113 degrees, so some coolant escapes into the expansion tank. You crest the hill and go down the other side....the coolant temp drops back to 100 degrees (or whatever) and the cooling "system" tries to draw back coolant to make up for the partial vacuum that is being created in the "system".

But, if the rubber hose doesn't have a PERFECT seal, it will draw air instead of coolant. The expansion tank will still be full, but the radiator will now have AIR in it.....Air doesn't do a very good job of replacing the coolant in a cooling system.

So, check out the WHOLE cooling system.

If it was mine, I'd be investing in a new radiator, hoses, viscous hub, thermostat, and water pump.....as well as the 2 gauges I mentioned above.

Roachie....Don't follow me....I'm lost!

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AnswerID: 612961

Follow Up By: RichieK - Thursday, Aug 10, 2017 at 16:50

Thursday, Aug 10, 2017 at 16:50
Cheers Roachie
very interesting explanation on how that reservoir stays full, I'm sure you've hit the nail on the head.
Unfortunately it doesn't look like I'll be keeping the vehicle due to numerous replies (here and PradoPoint) indicating that the auto trans is basiaclly the root of the problem and due for overhaul/replacement. The cost of this in addition to the cost of a new head is probably more than the value of the car, and I've already thrown 16k at it over the last year or so..

I should have put those gauges on a long time ago!

Such a depressing state of affairs!!
FollowupID: 883331

Reply By: Malcom M - Monday, Aug 14, 2017 at 08:05

Monday, Aug 14, 2017 at 08:05
The 90's eat heads.
Toyota originally sourced these from China and the aluminium is very poor quality recycled crap.
Somewhere on PradoPoint there's a picture of one thats been cut in half on a band saw. You can clearly see the layers of the recycled stuff that has not melted into one pool of metal.
I'm guessing that your mechanic installed another Toyota head?
Bad move. The one you want is made in Spain by a company named AMC. These are available in Sydney somewhere and are made from new (not recycled) quality aluminium. Never heard of one of these failing (we have a 90 TD as well).
Do a search for AMC on PradoPoint.

Think SMS Diesel Spares in Homebush are the Aus AMC agents.
AnswerID: 613051

Follow Up By: RichieK - Monday, Aug 14, 2017 at 08:27

Monday, Aug 14, 2017 at 08:27
Not sure where the head came from but it wasn't a toyota.. possibly a Chinese one though from memory. Anyway I'm not gonna put any more money into it, pretty sure ill be stripping it for parts soon..

Cheers mate
FollowupID: 883426

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