I have been having overheating problems for some time now, tried: changing rad cover, rodding out radiator, changing cylinder head gasket, and the last time I changed the fan clutch assembly(as shown in the diagram on Ace answers). I still overheat when I drive long distances at top speeds, but the ace runs fine around town(no overheating). I am thinking that changing the fan clutch should have changed the viscous coupling and so that was not my problem....if so, what could it be? I now thinking of "pinning" the fan in position to always spin at maximum speed.I live in Jamaica so I don't have to worry about cold climates. Advice anyone????
I drive a 1994 Townace, DX.

- (#8309) howard, 3 Feb 04 21:51

Hello Howard.
These sort of symptoms usually indicate that the viscous coupling is failing, but do not pin the fan to the drive pulley. It puts too much strain on the engine.
It could possibly be related to the thermostat, do you know if you have the correct 30mm Toyota thermostat? If the radiator fan shroud is missing or broken, it could reduce the effectiveness of the fan. Is it intact and in position? If you have a 4wd automatic, there will be a second radiator mounted horizontally under the floor, that could be blocked.

- (#8309) dave Bright, 4 Feb 04 08:29

The shroud is intact and in position. Ace is rear-wheel drive (I only see one radiator). When the overheating first began early last year I got the thermostat removed and it ran pretty good(temp slightly above cold)for several months, all over the country. Isn't the viscous coupling a part of the fan clutch(which I replaced with a new one in December: as the bearings was also well worn), so why would it still be failing. And if so, what then could my problem be? I realize that pinning the fan to the drive pulley is not the ideal solution, but I am now very frustrated, this problem is preventing me from going out of town and visiting my family.

- (#8309) howard, 4 Feb 04 11:10

If you had the thermostat removed last year, has it been replaced yet?
If not then that is almost certainly part of the cause of overheating. The coolant will be flowing too quickly to absorb the heat in the engine and loose it in the radiator.
2wd only has one radiator, so don’t worry, the 2nd one is only fitted to the 4wd.

- (#8309) dave Bright, 4 Feb 04 12:48

Yes Dave, the thermostat was removed but not not replaced. My mechanic told me that the thermostat opens the valve to the radiator to begin cooling, once the engine reached its ideal operating temperature(so that the radiator will prevent it from passing this temperature). He says that without the thermostat the engine will run cooler than normal, but because I am in a tropical climate (Jamaica is warm all year round) I don't have to worry about the temperature of the engine falling too low. From your answer I am now thinking that the water is flowing too fast through the engine block and thus not allowing enough time for adequate heat transfer at higher revs. If that is so, how do I explain the fact that the engine operated cooler for months and only now started to overheat again. He believes that the solution is to pin the fan, To me that seems to be attacking the symptom and not the problem! I know there must be a better way, but what?

- (#8309) howard, 5 Feb 04 05:17

put the thermostat back in.
toyota part numbers;
thermostat(30mm x 10mm) 90916-03046
thermostat o-ring 16325-63010

- (#8309) dave Bright, 5 Feb 04 05:36

As I understand it Howard suspects that his overheating when driving fast is because his new viscous coupling is not making the fan turn. It should do that once the coupling reaches a certain temperature. Maybe it's not getting hot enough? It's source of heat is the air that has come though the radiator so a key question is whether the radiator is actually getting very hot and whether the air passing through the radiator is heating the coupling. However my experience is that at 70mph (on the level) enough air is forced through the radiator by the car's movement that the viscous-coupled fan doesn't appear to need run at all.
I agree with Dave it's better overall to have the thermostat in (I lived in the tropics for 10 years so I've heard the pros and cons) but I would suspect that this overheating is caused by insufficient coolant flow - air locks, other blockage, water pump. As yet I'm sceptical that too much coolant flow will encourage overheating. Maybe Howard's using just water - that could be the problem?

- (#8309) Dave (Sussex), 5 Feb 04 07:17

Howard

i have read the above and i feel the problem could be your rad,how old is it,have you had it recored,do you use anti-freeze in Jamaica,in Japan they do not use it and you end up with the engine rusting from inside out
this can rust core plugs and block rads,maybe your rad is part blocked or the blockist is moving about,recore the rad and give engine a good flush out.

good luck

- (#8309) dennis, 5 Feb 04 08:27

If the thermostat was removed at the same time the Viscous coupling was replaced with a new one, then the likelihood is that the original cause was solved, and a new cause introduced.

Toyota will have designed the cooling system to operate with an optimum flow rate. Fit an aftermarket stat with an opening of only 25mm, and the flow rate is so slow, the cooling system overheats even in normal town traffic. Remove the thermostat completely and the opening becomes too big and the flow rate too great to transfer the heat. The chances are that it has been running hot, but the unmodified temperature gauge (that isn't good enough to indicate when the engine is running hot, only that its running very hot) hasn't detected it until now. 4 months ago was mid October when air temperatures were getting lower. Now they are getting warmer, it could affect the marginal cooling of a system with no thermostat control.

- (#8309) dave Bright, 5 Feb 04 08:47

Howard, do you have have anti-freeze, or I guess summer coolant adative, added to raise the boiling point of the water?
Is it automatic and fluid level ok?
Have you checked that the radiator is externally clear and free for maximum air flow?

- (#8309) Clive (Bristol), 5 Feb 04 08:48

Forgot, have you replaced the rad cap, can be a weak point in the coolant system?

- (#8309) Clive (Bristol), 5 Feb 04 08:53

Saturday I took the day to sort out the problem with this overheating again. took it to a reputable garage and got it pressure tested, the pressure held steady. We let the engine run with the air conditioner and headlights on, vehicle stationary, for about an hour, the temperature gauge barely moved above cold. We pressure tested again, it still held steady. The mechanic is saying that he is not so sure what is wrong yet, On Wednesday we will race it over the hill so that it will actually start overheating and then re-test it. He is asking about the timing. I changed timing chain approximately four years ago and did not have any overheating trouble then. Is that even a consideration? if so how would the timing just go bad?

- (#8309) Howard, 8 Mar 04 09:30

So it's a petrol engine then? Incorrect timing could cause overheating, yes...

- (#8309) david miller, 8 Mar 04 10:58

I have the same problem. about 2 years ago the head gasket blew and this resulted in a engin replacement.

Since then the car went well until I made a long journey when i noticed the temp kept rising and rising.

I have flushed the rad 3 times now and still have the same problem. Infact I think it is worse. I will replace the thermostat and some of the hoses as they look tired.
Will this help? Will this solve this problem. Does Toyota have any answers as they are the engine builders?

Like to have your views.

- (#8309) des sequeira, 8 Mar 04 16:13

Howard.
Have you replaced the thermostat yet?

Des.
It would be a good idea to replace the hoses and thermostat, it certainly wont hurt anyway. When you replaced the head gasket did you have the head skimmed and pressure tested for cracks? has your coolant turned black by any chance?

When fuel is burnt it releases energy. One third of this energy moves the van whilst the other two thirds produces heat. Half of the heat produced disappears out of the exhaust pipe and the other half of the heat remains in the engine. The harder the engine works, the more fuel it burns, and the more heat it produces. When these vans are motoring at speed, the engine under the most strain, burns the most fuel, which produces the most heat. If the cooling system is not in tip top condition, it will struggle to cool the engine sufficiently to prevent overheating. Meanwhile the van can drive around all day in normal traffic with out overheating, because even if the cooling ability is reduced, at low speeds the engine uses much less fuel which produces much less heat.

- (#8309) dave Bright (Bournemouth), 9 Mar 04 01:22

Well said Dave and, here I go again spouting my long held belief that Town/Masteraces are NOT motorway "burners". I am sure that Des treats his vehicle tenderly but, in the main I think many of the overheating problems are brought about by sustained high speeds, and a cooling system which has no great margin for coping with the extremes of higher temperatures. My motoring is quite sedate and leisurely and, I feel that this suits the vehicle but, continued high speed, with a vehicle where the engine and radiator are situated a long way from the,less than adequate, cooling air access, does, in my opinion, invite problems which the cooling system, operating on a knife edge, cannot cope with. Any modification, ie, to the thermostat, radiator/s, hoses, fan etc, which will help to keep the cooling system in tip top condition, must be a priority with these vehicles.
It would be interesting to find out if the 4WD version vehicles, which have the second, horizontal radiator, are less prone to cooling problems and, if this is so, is there a case for fitting a supplimentary tank, linked into the cooling system and increasing the coolant volume, which might act as a "buffer" at that critical high temperature point and which might give those vital seconds to reduce speed/load etc before the bannana head syndrome kicks in.

- (#8309) John Davis (Leics), 9 Mar 04 06:01

No special favours for the 4WD variants John. I know of Dave Bright, David Miller (twice) and myself all going down with banana head syndrome. No doubt there are plenty of other 4WDers on here who could add to the list. I agree whole heartedly with your view on high speed driving though.

As an aside, most of my journeys in the Townace are short, to take the dog a walk over the hills near Matlock. To get there I have to climb a hill and depending on whether I push it hard or not, the temperature will increase noticeably as confirmed by the Mason alarm. This is the point where the coolant is first coming up to optimum temperature. Subsequent hills (which are steeper) don't create this same effect, the temperature gauge doesn't climb as high. The problem goes away when running with my 'summer' stat in place.

So the inference is that it's not only motorway driving at high speeds that can create the problems its also prolongued high revs while getting up to temperature too. Finely balanced indeed!

- (#8309) Ian Dunse (Derbs), 9 Mar 04 06:19

Quite right Ian I have a 4x4 and suffered from a blown head gasket that led to a cracked head.
4x4 vans do have an extra radiator, but that is because the extra weight puts extra load on the engine that has to use more fuel which produces more heat. Another problem area I am wrestling with is the drawback mechanism and just how dynamic it is. The expansion of the coolant is due to the increase in temperature, so a big hill or short burst of speed that increases the temperature must also increase the pressure. The radiator cap will react to the increased pressure and limit it to 13.5psi. Once the hill is climbed, or the speed is reduced, then the coolant reduces in temperature and therefore so does the pressure. The drawback mechanism cannot work until the cooling system has reached negative pressure and sucks the spare coolant in from the expansion tank. Negative pressure will reduce the boiling point to below 100°C so it can't happen whilst the engine is running at its normal temperature of about 105°C. Obviously the whole thing works because by and large, most Townaces don't overheat all the time, only some of them overheat for some of the time. For what its worth, I think the cooling system design is capable of handling high speeds and big hills, we just have to remember that these vans are around 15 years old, and the cooling system may not be in its prime condition.

- (#8309) dave Bright (Bournemouth), 9 Mar 04 07:08

I've done the big hills (Alps), the high speeds (where legal on the autobahn), and yes the temp went up. I have a Mason Alarm fitted and yes it went off on the hills, not the high speed which was in air temp of about 30 degrees C. The time that I think is critical is when you stop and turn off. The coolant is no longer circulated and local hot spots could occur. Several times I have just stopped for a minute, restarted and the alarm is going off, it is hot where the sender is, and I assume most of the water jacket is also. It cools after a few seconds of running but has the damage been done?
I should add that I flushed the system several times and had a pressure check when I got it. I added Water Wetter to the coolant that may or may not help. I keep a check on the level and condition of the hose's, and always look for that little puddle just behind the passenger front wheel. But hey, if it blows it blows, I've had two trouble free years so far, in a car that was not that expensive to buy for what you get, and it still puts a smile on my face.
Try getting a hot pasty out of the Hot Box in a snow bound traffic jam, add on the pop-corn aroma from my Bio-Diesel and the smile gets so big it hurts.

- (#8309) Clive (Bristol), 9 Mar 04 08:00

Nice one Clive, and thanks for putting a smile on my face. Still grinning about the tyre-levers post. :-)

- (#8309) Ian Dunse (Derbs), 9 Mar 04 09:02

Hi all
I have a Hiace 3.0 Super Custom Ltd, following a catastrophic head failure and 1200 quid later am actually running, I would like to add my query to this, what if I was to add an auxiliary rad to this and an electric fan, I have had ideas but wonder if someone has done the leg work already, and if it was worth the cost in time and money?
My question arises because at present most of my journies are on the motorways.
Another query, what thread are the sensors likey to be, I am interested in adding temp and pressure sensors to the oil and water circuits?
I have been looking at the durite range, and fancy the triple array, not being a boy racer am not interested in the boost gauge;-)

- (#8309) Master_Simon, 10 Mar 04 03:47