Hello, Im new here, lots of good experienced people here, so here goes: Strange problem that seems to become more frequent: I drive a bit, often 50 miles, before this starts. Cabin heat goes away and temp gauge goes up. As if the waterpump cant get water through... If I give it some rpm, heat comes back and gauge is back to normal. It has to really get some windings, around 5000 will do the trick. If I then keep it around 4000, the problem seems to stay away... Coolant and thermostat has been changed. It has had a dose of Holts gold coolant treatment. Coolant is not bright red... Its not using any coolant after the Holts treatment, did before. Any thoughts?

I'd be extremely surprised if this has anything to do with the pump itself.

It almost sounds like your new thermostat is closing again, to test simply remove the thermostat completely and go for a drive, it'll take much longer to warm up but the loss of cabin heat and the gauge overheating should go.

Check for residual pressure in the expansion tank first thing in the morning before starting the engine.

14 hours ago, Wino said:

Check for residual pressure in the expansion tank first thing in the morning before starting the engine.

I have pressure in the system before starting...

 

16 hours ago, sepulchrave said:

I'd be extremely surprised if this has anything to do with the pump itself.

It almost sounds like your new thermostat is closing again, to test simply remove the thermostat completely and go for a drive, it'll take much longer to warm up but the loss of cabin heat and the gauge overheating should go.

Yes good plan. How are your experience with Holts?

1 hour ago, johnjorgensen said:

I have pressure in the system before starting...

 

 

Prepare yourself for dealing with a failing headgasket. That's really the only way that combustion gases can get into the coolant and create this extra pressure.

You may be able to get some visual confirmation by removing all the spark plugs, then turning the engine (forwards) by hand so that each piston crown in turn reaches top dead centre.  A bright torch shone down the plug hole may show you one piston crown with a different - steam-cleaned - appearance.

 

Leak-stop potions will only offer a very temporary improvement for a head gasket/fire-ring leak.

8 hours ago, Wino said:

 

Prepare yourself for dealing with a failing headgasket. That's really the only way that combustion gases can get into the coolant and create this extra pressure.

You may be able to get some visual confirmation by removing all the spark plugs, then turning the engine (forwards) by hand so that each piston crown in turn reaches top dead centre.  A bright torch shone down the plug hole may show you one piston crown with a different - steam-cleaned - appearance.

 

Leak-stop potions will only offer a very temporary improvement for a head gasket/fire-ring leak.

Tank you guys. I was afraid that might be the problem. Compared to changing the timing chain, how difficult (special tools, head skimming and so, would you say a headgasket is? I did change te timing chain, but this time of the year and no shed, is a bit nasty. (Id rather do my brit bikes´s than this one...)

Just now, johnjorgensen said:

Tank you guys. I was afraid that might be the problem. Compared to changing the timing chain, how difficult (special tools, head skimming and so, would you say a headgasket is? I did change te timing chain, but this time of the year and no shed, is a bit nasty. (Id rather do my brit bikes´s than this one...)

And good tip looking down te sparkplug hole!

19 hours ago, johnjorgensen said:

Compared to changing the timing chain, how difficult

 

Shouldn't be any more difficult, I don't think. It's not a common failure on these engines, so there may not be much info about.  There was one a few years ago where one of the headbolts had corroded/seized into the block and caused it to be a tricky job, I think it was @hutchysrs50? Might be wrong about that. 

Worth getting the head checked for flatness and skimmed if necessary before refitting. Would also be a good idea to check the valve guides for play and maybe replace the valve stem seals. All adds to the cost and downtime, but they are the sort of things that you'd really regret not doing while everything was apart, if you didn't do it. 

Thanks. What puzzles me is that the nproblem usually come when I drive on level road at 3k rpm in top gear, with very little load on the engiune. I would think that more load on the engine, would cause the problem if its the headgasket?. And why would the cabinheat disappear if engine is getting more hot? I thought that the wqterpump might have lost some wings and therefore gave better circulation at higher revs... Where is the logic in this problem?

The symptoms don't make sense, increasing revs should increase temperature.

I don't think the water pump could just fall to pieces either.

Consider how gas bubbles in the coolant might affect waterpump function, and the heater matrix.

High revs may re-establish good liquid flow?

Yes, that's the only other possibility, that the additional coolant flow at high revs is just enough to overcome the airlock formed by combustion gases.

If the OP does have a pressurised cooling system when stone cold then HGF is certain.

Yes that makes sense. Thanks mates....

Do try the 'look down the sparkplug hole' thing, it's nice to have some sort of visual confirmation.  On an old Vauxhall we used to own, I even saw a little puddle of coolant sitting on the piston crown of the affected cylinder.  If you do see any fluid there, take a sample with a bit of clean white tissue taped around a stick; if it looks & smells like coolant, you'll have very solid proof.  

 

Edited 27 November, 20196 yr by Wino