Overheating - what next?

[Axolotl]

Hi, I've not posted here for ages, mainly because I've driven so few miles in my Traveller (350 miles between MOTs ) that nothing's gone wrong, and there's been nothing to report, until now.

The car has developed an overheating problem that I can't get to the bottom of, and I'm looking for ideas.

The symptoms have been progresssive, in that I first noticed a problem on a fast drive on dual carriageway (60 mph plus). The temperature gauge suddenly took off from normal, where it has been for past 5 years, towards the red zone. I pulled off, and slowed down, back on normal roads, and it returned to normal.

A few more trips, and it would be fine if I stuck to pootling about under 40, but start the overheating as soon as I drove fast any distance. It would take ages to cool down when I slowed down, but did cool down.

After checking everything I can think of, (see list below), the overheating has now got so bad that it will do it after just a short drive at 30 mph, and it doesn't cool down until I turn the engine off.

It is a 1971 Traveller with a standard 1098cc / 4 speed box. I have a temperature gauge fitted, along with ammeter and oil pressure.

In my efforts to track this down, I have checked (and adjusted where there seemed to be any doubt) the following, pretty much in this order:-

- Binding brakes. (Marina disks on the front, 7in drums at the back, fitted new drums, shoes, pull-off springs and adjusted just right. They aren't warm when I get home from a trip.

- Timing. Spot on as far as I can tell.

- Mixture. Again, just about as right as I can get it.

- Stuck thermostat. I have an 88 degree one in, and boiling it up in a saucepan shows it opens at just the right temperature, as does checking the heat on the thermostat housing, top hose and radiator header tank when you can see the rise as it opens. (Using a remote infrared thermometer thingy). I have also tried with no thermostat, and if anything it overheated quicker, resulting in a classic brew up at the side of the road. Incidentally, that ruled out another possibility: that it was a gauge fault. I guess boiling over when the gauge says "it's going to boil over" means the gauge works.

- Blocked hoses. I have replaced top and bottom hoses, in case there was an internal collapse blocking water flow.

- Loose fan belt. It isn't. I can just turn the fan by hand against the belt friction, and my alternator is charging o.k.

- Blocked radiator. This was a new (recon) radiator fitted just after I got the car 6 years ago. Flushing water in at top or bottom results in a healthy flow out the other end. Using the remote thermometer shows a pretty even heating across the matrix, with 80 - 100 degrees C at the top (112 when it boiled over), and 60 - 70 degrees at the bottom, on the return hose.

I think I'm left with two possibilities:-

- The water pump rotor isn't turning, even though the pulley is, so there isn't the flow there should be, just thermo siphon effect. Is this possible? There don't seem to be any odd noises, but I guess it could become detached somehow? I can't see any obvious turbulence in the radiator if I take the cap off and run the engine until the thermostat opens. Since I've never looked before, I'm not sure what I should see here?

- Head gasket blown. The engine doesn't seem down on power. A quick compression test reveals, front to back (psi):- 165, 145, 150, 150. Any way I can tell if this is the problem before i get the head off?

Either way, I think I'm looking at getting the manual out again to do some serious stripping down, unless someone can tell me what's causing this, or suggest other things to check before the big stuff.

Thanks in advance,

[mike.perry]

Compression readings are OK for head gasket. Check no oil in water/water in oil
Water pump needs more investigtion, remove fan belt and check for play on the shaft
What temp gauge, capillery or electric? If electric is sensor ok? Is it connected through voltage stabiliser? Is V/S OK?
Have radiator checked, it will still pass a hose pipe of water even when the tubes are partly blocked

[bmcecosse]

I suppose the block could be choked with debris/scale - but as you have diagnosed, the water pump must be the main suspect. I would fit a 74 degree stat for summer use - 88 is fine in winter! But that's not the answer here.

[Declan_Burns]

I would also suspect the water pump-perhaps the impellers have disintegrated.
Regards
Declan

[kennatt]

one check for water pump before you do anything else,with cap off let it get up to temp(Themostat open) gently rev the engine and watch the water level,if the pump is working you should see the level drop slightly as the pump draws water through the system. If no movement at all then yes water pump off.

[Axolotl]

Sorry about the delay, been a bit busy this last week.

In answer to some of the posts above, I did actually get it boiling over when the gauge went into the red zone, and the gauge is on a voltage stabiliser, so it wasn't the gauge (although it does under-read slightly compared to readings taken with the remote infrared thermometer).

The good news is that the overheating is cured. The bad news is that it seems the culprit was the radiator (again).

I took the old water pump off and it seemed to be perfectly serviceable, apart from a little corrosion externally and a slight squeak from the bearings / seal. Certainly no blades gone, and the impellor was locked to the shaft and pulley mount.

I decided to replace it anyway. In taking the pump off, I managed to poke a hole in the radiator ( ) - don't ask.

I fitted a new water pump, a new recon radiator from ESM, new bypass hose while the pump was off, and a new thermostat housing for good measure. I kept the old thermostat in place.

Having put it all back together and filled with 50% antifreeze mix I've taken it for a run, 40 miles of motorway thrash and local roads and traffic jams, and the temperature gauge reading is back to what I'd call normal.

It sits at about 165 degrees F (74C) in normal running and rises to about 175F (79C) on the motorway, just like it used to before all this began. For reference, 180F (82C) is the halfway mark on this gauge. I think the numbers aren't actually that important, the fact is that it now stays more or less where it is about in the middle, and doesn't climb steadily into the red.

Checking the new radiator fins with the remote thermometer, it seems to be hot all over now instead of very hot at the top and cooler at the bottom but the outlet hose at the borttom is about 10 - 20 degrees C lower than the inlet at the top.

Since there was nothing seriously wrong with the old water pump, I think the problem must have been the radiator being partially blocked, but the effect seemed to be very dramatic, came on quite suddenly and got rapidly worse very quickly given that some water was obviously flowing through it.

Question now is, is there anything I can do to "descale" the system so the new radiator doesn't clog up like the old one? Bear in mind that when I got the car seven years agao, it needed a new radiator then to cure overheating, and it seems it now needed another one?

I notice the workshop manual recommends using rainwater to fill the cooling system, presumably because it is soft. I live in a very hard water area, but have always used tap water to fill the system, so could tap water be the problem causing or aggravating scale?

Thanks for your help and suggestions.

[bmcecosse]

Hard water won't help - but really now, that water should stay in the system for the next ten years - so don't worry about it!

[Axolotl]

Thanks. I'll leave it as is. Just seen the price of antifreeze!

By the way, my mistake, the thermostat in there now is 82C not 88C. I must have changed it when it first started overheating as one of the things to try, and forgotten about it.

[MarkyB]

My guess is that they screwed up recoring the rad somehow, squished some bits to make them fit, used too much solder and blocked stuff, dunno.

[mike.perry]

You are just up the road from me (Tilehurst). The water comes out of the taps in bricks around here