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?
So..
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!!
Richard