Thread: Old auto Mazda 121

Geez the list of what it could be is long.

Is the fan belt on tight as a slipping belt will cause the car to overheat at speed.

Is the water pump OK, if the blades are rusted as the engine spins faster it cannot pump water?

Is the thermostat opening all the way, as the engine speed increases you need the thermostat to open far enough to allow water through.

Is the bottom radiator hose with a spring inside? As the water pump draws water the hose can collapse and restrict flow.

Is your radiators air passage clear, no rubbish blocking air flow?

Is you radiator blocked internally?

Is your water level dropping?

Is your cooling system holding pressure?

Is your oil turning milky white, water level dropping and maybe running rough?

Id start with checking the belt tension, replace the thermostat, maybe remove the radiator and reverse flush it (internally and externally) for a start.

A new fan/alternator belt as well as a drive belt were fitted 2 days after the problem surfaced, as the belts were starting to scream.

This made no difference to the heat going up. Just like colamus says he has watched/observed, then this is the same.

I guess I'll start at the easy parts you suggest, and tomorrow check the bottom hose.

The oil shows no sign of milkiness.

The radiator never uses water, think it has only been topped up twice in 12 months...just doesn't seem to need it.

The radiator seems clear of anything, allowing air to be blown over it ok.

How do I check for an internal blockage or that it holds pressure?

As usual...many thanks for trying to assist.

Originally Posted by Coldamus

The temp gauge always used to sit just under 1/2 way no matter how hard or how long I drove the car. Then it started getting hot if I went over 100kph even for a short time. If I don't slow down, it quickly goes well over 3/4 on the gauge. Slowing to 100kph does not bring it back down. I have to slow to 80kph or less. It is fine then, even in the thickest of traffic.

i'm thinking that combustion gases are entering the cooling system at higher loads and temps , maybe from a slightly loose head gasket. only needs to be a small amount.

Like Tradesman said it could be a hairline crack in your head.
My brother just went through the same ordeal.

try retensioning the head bolts first , as its a good place to start. if the centre ones are a bit loose it may confirm a leak.

Once a gasket starts to leak it's game over.

Tightening head bolts rarely helps as a cut would already be present.

That's why I asked if the water level was dropping or if the oil was turning milky or if the engine was running rough.

Once the head gasket leaks it's head off time for a proper repair.

A cracked head or gasket could explain mine but I hope not. There's certainly no sign of it at idle - i.e. no bubbling visible when looking through the radiator cap hole. Also it runs smooth and has plenty of power. However, when it is hot it does blow through and overflow the reservoir bottle.

For example, I drove to Tamworth this morning (75kms). The temp gauge was on 3/4 when I got there. It cooled off a bit when parked while shopping. When I started it again, the gauge was at 1/2 way. I replenished the coolant (about 1 litre) with the engine running and the gauge then stayed on 1/2 way for the whole 75kms back home.

If it is the head gasket or a cracked head, it will probably get worse rapidly, so I suppose we will know soon enough. In the meantime, I will replace the bottom radiator hose on mine. I already replaced the top one as I had a spare.

what about a restricted exhaust pipe or catalytic converter, could that cause overheating at high speed but not at normal town speed.Because all the other things like thermostat, water-pump ,slipping belts etc . seem to effect idle conditions like traffic lights etc. and he's not complaining about overheating in that situation.


Dash.

Ok..update day.

The alternator or drive belt only squealed on start up, and stopped after 30 seconds or so. It never squealed or made any noise at other times.

Today I took off the top and bottom hoses, and flushed out the radiator...not much gunk came out, but others at work said you need rods or something to clean the guts properly.
Anyhow, the hoses were all in good nick, so I refitted the hoses and clamps, and topped it back up with water. After startup, I also ensured the radiator was fully topped and the side water bottle filled to the designated height. I didn't fill it with coolant at this stage, as I thought if I need to remove hoses or anything again, then that was a waste of good coolant.

It seemed to come on to temperature very quickly, from just a few minutes idling, so I turned it off.

As I say, I am a car dummy, so I just poked around, not really having much of a clue.

What I noticed next was a yellow warning sticker on the electric radiator cooling fan, warning that the fan operates as soon as the ignition is turned on...so I went and turned it to the on position, and I couldn't hear the fan. I started it up, and still can't hear the fan. I got the missus out with me and we both took a turn at starting the car, and looking to see if the fan moved...it never did.The car does not have a fan belt, it is reliant on the electric fan.

I then found the 30w fuse in the engine bay, marked "cooling fan" and checked that..it looked ok. We noticed another fuse in this batch of 4, was also another 30w one, so we swapped them to try work out if the fuse was faulty...unfortunately, no difference, so fuses does not appear to be the problem.

I guess I need to carefully drive it to either a radiator place or an auto electrician to see if the fan motor is buggered or not....that's a 35km trip on an 80-100km country road. Also not sure if a new one just bolts on to the outside of the radiator, or you have to buy a relacement all up. This fan is on one outside radiator, and there is another radiator on the iside of that one, about 25mm apart. I suppose one is maybe for the a/c and one is for the engine cooling?

Am I on the right track?

Thanks for everyone's input so far.

Originally Posted by weirdo

You could test your fan by just hooking it up to 12 volts viewer but I somehow doubt this is your problem since you stated the problem is present at 100 kph. The electric fan is often for when it overheats (more likely on hot days in crawling city traffic) or fitted for your AC.

Oh bugger....smacked in the back of the head again...lol

lol sorry mate

To test your thermo fans, take the car for a drive, let it get hot, pull over and pop the bonnet.

They should switch on at some stage within 5-10 minutes of being stationary while the engine is running.

Also after performing that test, turn on your aircon, a fan should also start.

Now here is the fun part, your fans should no need to turn on while your doing 100 as the airflow through the radiator while you are moving is far more than it should need.

I dont blame the fans, because your not overheating at low speed when there is no or little airflow.

Still waiting to hear why your belts squeal, are they loose of is your waterpump farked?

Originally Posted by Godzilla

Still waiting to hear why your belts squeal, are they loose of is your waterpump farked?

From my update Godzilla...
Ok..update day.

The alternator or drive belt only squealed on start up, and stopped after 30 seconds or so. It never squealed or made any noise at other times.