I've just had a new(recon) head put on mu 4WD Diesel Townie, and it seems like there's still a heating issue to deal with. My mechanic thinks it might be a blockage in the water flow somewhere, since the heater blows hot and then stops when up tio idle speed in the garage (no overheating in garage, jus on M-way).
Searched archives and found this;
Steve front first - check the inline valve is operating, this can be found underneath at the front, should be able to move it by hand, once open hose should get hot. Rear should have a hot feed and warm return again under just in front of where the battery box sticks down, if ok may be duct flap stuck on cold/lever not connected.
If still cold may be airlocks/blockage/pipe-tube damage.
Give the whole system a good clean/flush out.
HTH Clive
- (5993) clive, 29 Oct 02
Can a blockage such as this cause overheating? Don't want my man to waste his time and my money pulling the heater out to check it.
Thanks,
Raheem.
- (#13635) Raheem, 6 Oct 04 14:18
Hello Raheem,
if your 4wd is automatic, it will have a second cooling radiator mounted horizontally under the front floor (where the air conditioning fans are also mounted). Any restrictions in this radiator can cause overheating under heavy engine loads.
Overheating on Motorways, has been known to be caused by a failing viscous coupling. If the temperature rises whilst travelling at 70+ mph (revs over 3,000) try slowing down a bit so that the engine revs are below 3,000. If the temperature reduces, it would point to the viscous coupling.
It would also be wise to check the rubber seal on the radiator cap for splits or cracks. Any signs of wear and its best to replace it with a Toyota float type cap.
- (#13635) dave Bright (Bournemouth), 7 Oct 04 07:06
Does the coolant, cold, stay within 30mm of the filler cap?
"heater blows hot and then stops when up to idle speed" is an odd remark. The rear heater (turned on) should start blowing warm within one or two minutes and continue doing so. The rear heater matrix takes it's own continuous (no valves) feed from the head and returns it into the block beside the thermostat - and when that flow is hot enough then the thermostat opens to allow flow through the radiator. It's a serious fault if the rear heater works at first but then "stops" passing warm water, though that's most likely caused by airlocks in the system - drain (and a good flush would expel sediment that might be causing a blockage) and then refill very slowly.
- (#13635) Dave Mason (Sussex), 7 Oct 04 08:12
Thanks to Dave Bright and Mason for your answers. My mechanic has now bypassed the horizontal radiator, since the aircon wasn't working anyway and he's trying to narrow down the problem by elimination. Should the cooling system work properly in cooling the engine under these circumstances?
Suggestions/comments most welcome because he's really struggling with this one, and any tips that might help would be much appreciated.
- (#13635) Raheem, 13 Oct 04 13:14
Raheem. In my opinion, bypassing the horizontal radiator is not a good idea. You have a larger volume of coolant available with the two radiators and this must be a good thing. The horizontal radiator is installed to give extra cooling for 4WD vehicles running over extreme surfaces at low speeds and very high revs, and has nothing to do with the air conditioning system. Is your mechanic confusing this radiator with an evaporator? The fans, above this radiator, are part of the aircon system but, at extreme temperatures, they, too, will operate to draw air through the horizintal radiator.
Yes, the cooling system, with the one vertical radiator, will work and this is the system which is installed on the 2WD vehicles but, that extra radiator, with it's extra coolant volume, is a big asset even if you are not motoring in 4WD up the side of a hill.
The comment "re-fill very slowly" cannot be stressed too highly. There are many odd bends and crevices in this cooling system and re-filling must be done very slowly to allow the air, which is being pushed out by the refill, to escape from these traps. Even then, squeezing all the hoses after a short engine run, will produce some more air. Yes, a blockage in the rear heater could, in theory, create overheat conditions because this feed & return pipe is a bypass to the main engine thermostat. If the heater pipe or matrix is blocked, and the engine thermostat is at all suspect, there will be a very quick warm up.
Your mechanic should check or replace the thermostat and, also, disconnect the feed and return pipes, at the rear heater, couple them together with a short piece of rigid pipe (15mm copper), and see if there is a hot flow, through this pipe, back to the engine.
The heater matrix can be tested in situ by flushing it through with a low pressure, low volume hose pipe.
- (#13635) John Davis (Leics), 13 Oct 04 14:32