Overheating - Just Sometimes + Heater Being Odd - Mechanics Cant Diagn

[dannyoneill4242]

Hi all,

I hope someone can help me, am having an overheating issue that so far no one can solve!

About a month ago my Yaris D4D 05 started having intermittent overheating when driving up very long hills or going over about 65. The behaviour started very much one day and immediately started doing it every time I drove up a hill. At the same time - same day I started getting intermittent heat from the internal heater.

The car has 150k on the clock and I've had it from new. It is in good nick otherwise, plenty of power still, good ecconomy, and up until this behaviour literally never over-heated.

Things I have tried listed by possible causes:

1) Loosing water:

- It's not. If I drive under 55 and the warning light never comes on, then the level doesn't drop, not at all.

- The symptoms persist even when I have JUST filled the heating system. And I mean I can fill it, drive hard and cause the over-heating light and then stop and check the level and it will still be just the same.

- The only time it actually looses water is if I do a really long journey with hills that I cannot avoid and so it overheats multiple times (I pull over if it does it for more than 30s but still very worrying). And even then only a little, Just a cup full or so, so I presume it is just getting to a high pressure and some is escaping from the expansion cap.

2) Head-gasket:

- It's not loosing water.

- No bubbles in coolant when looking into expansion tank and revving.

- The overheating happens when the system is full of water and as far as I understand it, over-heating due to cracked cylinder heads and busted gaskets is a secondary symptom which follows the loss of water.

3) Thermostat:

- Old one taken out and dunked in hot water and compared to new one, was absolutely fine.

- Replaced it with new one anyway.

- Return pipe from engine to radiator stays cold for about 4 mins and then suddenly gets hot, which according to the two manuals I have now bought is the correct behaviour if starting from cold with a correctly functioning thermostat.

4) Water pump:

- Old one taken out and was absolutely fine.

- Replaced it with new one anyway.

- When the heater is working there is plenty of heat.

- At any time, if you come off the gas then the engine will cool back down, so there must always be at least some flow of water.

5) Heater matrix blocked:

- Water blasted through heater matrix and no blockage found - done via pipes going though firewall - took both off and put hose on both ends and plenty of water came out in both directions.

6) Radiator blocked:

- Tubes too big for me to force water in easily from hosepipe, but certainly it drains well and water comes out fine and have done this 5 times at least now. Doesn't look too hard to get out so could replace, but seems like it would have to be very blocked to stop internal heater from working at all and that cant be the case given that at normal speeds the car DOES cool itself quite well.

7) Temp guage broken:

- The warning comes on when the car is pushed hard (after about 20s) and it will turn off again if you come take the pressure off (go down the other side of the hill usually!)

8) Airlock:

- Not impossible that this is present and causing the heater issues / all of them. Have tried filling with expansion cap and radiator bleed off, front jacked up, front jacked up with rears chocked and car on a hill (not kidding), running, not running, both caps off for 5 mins and topping up, 30 mins of getting hot and still topping up, squeezing all pipes occasionally + Just about every combination of the aforementioned, must have refilled 10 times at least!!

- The level does move up and down a lot while running. When I take the cap off (after cooling) it always returns (no overall loss) but does move about a lot once it's hot. The heater stops workign the moment I'm below 55 (see point below) so haven't been able to see if level really drops in e-tank while heater is working.

A few observed things:

- The heater WILL kick in sometimes and when it does it goes instantly from cold / outside temp air to HOT air in seconds and can sustain it.

- It can be made to kick in by doing about 55-65mph for about 5mins, if you stay at that speed it will stay on and produce as much hot air as it ever has.

- Going faster than 70 and the heater will stop again and cold air will come out.

- The overheating is very odd - it will do it if driving hard (hills, high speed, overtaking) after about 20s. Pretty much as you'd expect for a just sub-par cooling system. The car has always been very efficient and if you come off the gas then the temp warning will go away again. HOWEVER: on a long drive last weekend I noticed that sometimes the engine would cool down BEFORE summiting hills, as if just sometimes the blockage or whatever it is, clears and the car is able to cool itself properly again.

I've phoned a few garages, inclding two local Toyota dealerships, but all they suggest is "water pump, innit mate? or maybe thermostat." and then offer to do an unguaranteed diagnosis for £150 ($225). That's just to find the problem and thats with no guarantee, so if they rebuild the whole engine and the issue persistes I get nothing back, and they'd probably just tell me the car is old and bound to overheat.

Any help or suggestions appreciated. Appologies for long post, but with such a well-discussed issue, I thought I'd get nothing but all the things I'd already tried if I just said "car overheating now and again".

Thanks!!!

[TomdeGuerre]

That’s a very comprehensive write up you’ve done there Danny and I congratulate you on it. You seem to have covered all the routine (and one or two not-so-routine) checks and tests. My bet is it’s most likely to be the cylinder head gasket on the way out or crack in the cylinder head,.I’ve seen this type of thing lead ppl on a merry dance before.

Don’t waste time looking for bubbles while you rev the engine. For one thing you’ve usually got to remove the thermostat to see that and in most cases you won’t see anything.

You say you have two caps, one on the radiator and one on the expansion tank. Are they the right way round? Get the pressure relief cap tested to make sure it is still at the right setting.

Get the whole system pressure tested, I don’t know the figures for your car but it may be something like 15 psi for 10 minutes and see if pressure drops.

Get the cooling system sniff tested for the presence of combustion products in the water.

[dannyoneill4242]

That’s a very comprehensive write up you’ve done there Danny and I congratulate you on it. You seem to have covered all the routine (and one or two not-so-routine) checks and tests. My bet is it’s most likely to be the cylinder head gasket on the way out or crack in the cylinder head,.I’ve seen this type of thing lead ppl on a merry dance before.

Don’t waste time looking for bubbles while you rev the engine. For one thing you’ve usually got to remove the thermostat to see that and in most cases you won’t see anything.

You say you have two caps, one on the radiator and one on the expansion tank. Are they the right way round? Get the pressure relief cap tested to make sure it is still at the right setting.

Get the whole system pressure tested, I don’t know the figures for your car but it may be something like 15 psi for 10 minutes and see if pressure drops.

Get the cooling system sniff tested for the presence of combustion products in the water.

Thanks for the feedback Tomde.

Two caps def right way round - diff sizes.

Will see if pressure relief caps are cheap (after checking right setting).

And after that take to garage and get it pressure tested and sniff tested. Was hoping to leave those till the very last thing as garages in south east england are just a massive rip-off - was quoted £250 to 'diagnose' the problem, I quizzed them and it turned out that even for £250 the diagnosis wasn't guaranteed in any way, they'd still charge for all work and parts and give no refunds if the issue persisted :(

(N.B. new radiators were cheap so I swapped that out too! Still no luck; poor thing still overheats at soon as it is pushed at all.)