Overheating at speed

[Sheepdip]

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I was thinking about this on the way in this morning as I noticed my Mondy gauge nicely resting at 1/3. I've always experienced hot running with both my Stags (both auto) and both rebuilt at times with no affect. New rad and cleaning block made no difference. One has 6 the other 12 vane. Temperature probes on engine revealed LH head rear was the hottest of the lot. Running the heater and popping bonnet made no difference.

Could the problem be getting the water out of theblock in the first place? It all has to come through the inlet manifold and assumes water ways perfectly aligned with the heads?My manifold is tight to assemble and wondering if head skimming has squeezed it up?



Sheepdip

[toneil461]

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Hi,

I read no mention that the thermostat has been checked. If this does not fully open (I mean fully open) then you will get the symtoms you are experiencing. Have you replaced the pressure cap?.



Terry..

[GDPR]

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I have just removed the rad for a thorough chemical flush in the morning with some stuff I got from a heating engineer pal - at the same time I will be removing the 'stat and testing it - might just fit a new one regardless. My rad is definitely 3 row core, cores in straightalignment and zigzag finning.

Pressure cap is new and full pressure is maintained when hot - no abnormal squirty leaks back into the expansion tank.

I have noticed that the heater pipe from the LH head is going to the upper heater matrix stub - this should be on the lower one I believe for a late mk2 so will reverse them in case it's causing a partial airlock.

I take sheepdip's point about misalignment of the head/inlet manifold waterways, but not convinced this is my problem - I have noticed that my antifreeze concentration is nearer to 50% on checking with another tester - it seems to be more viscous than I would expect so will reduce concentration to 30% to aid flow as well.

Opening the bonnet when at high speed makes no difference to temp at all so I'm ruling that one out too.

I am going round the M25 from J6 at Godstone to the M4 tomorrow night so will have a chance to assess what I have achieved and make plans for further work if required. I'll let you know what happens...... quite late if I have to involve a breakdown assistance service.....

Russ

[redstag]

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Hi

Have a look at the SOC websitetechnical section from around page 86 where they have tested several cooling set ups.

From your description it sounds like you may have a rad design that performs particularly poorly at high speed.

Pete

[DJT]

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Russ,

When you refill the system, take care to remove all the air. Have a look at what I wrote on the Radiator Coolant thread started by Marty64. Taking care to get as much water in the system as possible makes a lot of difference, particularly at speed.

BTW, I found that swapping the heater hoses over made no difference.

Dave

[Sheepdip]

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I looked at the heads from my wrecked engine last night - one of the inlet gaskets covered about a 1/4 of the waterway. I was aware of casting misalignment issues and I've seen some comments on this in another thread so hope I'm not repeating them.

Looking at the waterways it occurred to me that there's not much of a hole in the inlet manifoldfor water to escape from each head - in fact considering the size of waterways in block they're minuscule! Its a long time since I visited thermodynamics at college but my simple mind says that any restriction or misalignment between the waterways is not going to help water flow, and in my case would impede flow by 25% on one side all things being equal.

I've usually fitted payen gaskets as told "they're the best" - what are the alternatives like or any other suggestions ?



Sheepdip

[GDPR]

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Update: 14:30

The rad has been thoroughly descaled, but surprisingly didn't get as much brown clag as I thought I would - ever optimistic!

Rad refitted, and whole cooling system flushed with Holts 2 stage Radflush, that's when I discovered there was NO thermostat........

Fitted new stat, and then flushed whole system again with Wynns radflush - I will add I removed the block drain bungs on both sides on both flushes...

Refilled with coolant at 30%, and run up stationary for quite a while - gauge dead on halfway - washing up to leave for Windsor in a few minutes, so wish me luck!

[GDPR]

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I'm home - and still have an intact engine!

Temp slightly better on the motorway on the way there, with less use of heater - stayed in Windsor for a spot of dinner and an ice cream by the river so came back with dusk (and outside temp) falling.

This saw my temp running at halfway even with giving it a little bit of right foot and enjoying being able to use what is a very sweet engine with a few more revs than I have been daring to use.

Now totally convinced it's my poorly designed 3 row core rad and will be ordering one of Mr Hart's finest Supergills in the morning if he's open. My flushing antics definitely helped though, so a worthwhile job done, and won't have to do it again for a while.

The previous owner obviously removed the stat to try and overcome the radiator's shortcomings and not to mask something more sinister...:shock:

Cheers for the help lads, kept the old brain going

[DJT]

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Russ,

Glad you could enjoy it and had a good day out.

I would still recommend jacking up the front passenger side in the morning and removing the filler plug. I would be surprised if you couldn't get another half pint of water in there and this would drop the temp another few degrees.

Try it before spending out mega money on a new rad.

Dave