GT6 overheating

[Bob Horner]

Just thought I'd share my experiences.

I've just put a GT6 mk2 back on the road. It's running on a late Mk3 engine.  Despite idling happily without overheating as soon as I drove it, the temperature gauge started rising in to the red.  The engine was flushed with all sorts (including Fernox) but vey little crud came out from flushing and the drain at the rear of the block refused to do anything but dribble slightly (despite, bits of wire wiggling etc).  The heater was lukewarm at best (although did help a bit to cool the engine if on full with the fan blowing).

In the end bit the bullet, took off the cylinder head and after protecting cylinders etc with cloths, had a good go at cleaning out the rear of the block.  Not surprisingly full of crud and scale.  It didn't take too long and had it cleared out and running clear with water.  The head was also pretty gummed up so treated that to a flush with phosphoric acid (40% strength bought off ebay).  This latter substance is somewhat controversial - John D swears it wont work (only read his posts after buying it on someone else's recommendation).  Anyway, it fizzed away for a few days and cleaned up things a treat.  As the head was off I was sure I could rinse it out thoroughly so decided to risk it.

Cleaned up the head, lapped the valves, got a new gasket and put it all back together.  Far more hassle changing a diff.  All working well, engine now not overheating, rear drain working perfectly.  Heater is proper hot (not necessary I gather in a GT6 but nice to see it can work as expected).

Moral of (my) story.  Bite the bullet, don't arse about flushing and re flushing.  Don't replace all manner of items (bought a very nice aluminium rad which I'm sure I don't need but then it does reduce a bit of weight up front!), water pump etc.   Chances are your overheating issue is a cruddy block (especially if the drain doesn't work) and you may as well have a go at sorting it. 

Bob

 

 

 

 

 

 

 

 

 

 

[Pete Lewis]

thats good, i was thinking the end of the job was going to be the voltage stabiliser  giving high reading 

but nope  just crud 

pete

[Bob Horner]

Yes, should have mentioned that some of my pointless purchases were a couple of temperature senders and voltage stabilisers first!  I know its often said overheating is down to these.  However, in my experience (tr4, spitifre and now this) its always been something else to do with airflow, or water circulation.  The gauges havent lied - as much as i wished they had!  

Bob

[NonMember]

I've certainly had gauges that lied - in both directions - as well as engines that genuinely did overheat due to cooling system malfunctions, mostly leaks, although the car that managed ALL THREE (fake cold reading, fake hot reading and genuine overheating) was just a slipping fan belt.

I've also had a 2500S with the most comprehensively crudded up and totally blocked cooling system I've ever seen... that never overheated and somehow managed to have a half-decent heater. I still can't understand how it managed that.

[Nigel Clark]

The 6 pot motors build up an awful amount of sediment/scale/cr@p around cylinders 5 and 6, due to poor coolant flow at the back of the engine, when the pump is at the front. In my experience, the only way to clear it properly is to poke out the crud with a sharp implement once the head removed, down through the coolant passages and through the drain plug at the back of the block. Small screwdrivers and coat hanger wire will get the job done. Needs a lot of flushing too but chemical flushes won't touch this stuff, it has to be poked out.

Nigel

[dougbgt6]

The drain plug is in a reservoir to the side of the main waterways. Mine is irrevocably blocked with casting sand, since day one I believe. No amount of poking with screwdriver or coat hanger can shift it. All this means is I can't use the drain plug. But flushing the rest of the system is a very good idea, I use washing soda.

Doug

[JohnD]

Bob, 

Interesting to hear your success with Phosphoric acid.    Do you live in, or did the car live in a hard water area?    Perhaps there was lime scale in the coolant?    

The reaction of H2PO3 with rust doesn't "Fizz"!   But it would with carbonate.

John

[Colin Lindsay]

Maybe H3PO4 does?

[JohnD]

Ah, that's the heavyweight version!

[Nigel Clark]

1 hour ago, Colin Lindsay said:

Maybe H3PO4 does?

That's the correct formula for phosphoric acid... The main constituent of Jenolite. It is very effective in dissolving rust, and passivating iron and steel surfaces.

Nigel

[Colin Lindsay]

Yes, but I'll have to confess... I found that online when I was doing a bit of research on the stuff - prices, quantities etc.

I do like Jenolite, though.

[Bob Horner]

2 hours ago, JohnD said:

Bob, 

Interesting to hear your success with Phosphoric acid.    Do you live in, or did the car live in a hard water area?    Perhaps there was lime scale in the coolant?    

The reaction of H2PO3 with rust doesn't "Fizz"!   But it would with carbonate.

John

Possibly - not sure where the engine had resided most of its life.  When I say "fizzed" perhaps more correct to say it "foamed"  

Bob

[JohnD]

Same difference!

[Bob Horner]

Thought so!  But no chemist - clearly!

[GT6M]

It fizzys quite nicely, and after 3 rinses I had a heed an block  back to bare metal.

cleaned oot every bit of crud,rust there was

 

And it works even better if it hot, the hotter the better, can even dilute it alot moer than normal

BUTT, word of warning, it will also clean the core plugs of crud protection,

so may weel fin that thee,s will start t,leak  if no been replaced

 

Re over heating, most ive come across is cos the rad is no shrouded

and if fins ont rad are deformed, flattened agenst rad, then air cant get thru it as good

bit of a prob fitt,n a shroud on a VIT, but on a GT, its a must, top,sides an bottom all enclosed

so all that comes thru grill,goes thru rad

 

M

[Nick Jones]

1 hour ago, GT6M said:

but on a GT, its a must, top,sides an bottom all enclosed

so all that comes thru grill,goes thru rad

Absolutely.  There's a Mk2 Golf radiator under that lot and it works very well, because all the air goes through it

There's a plate on the chassis rails as well but I don't have a pic of that.

Nick

[NonMember]

Apparently my GT6 must be an oddball because it's never had a shroud (or engine bay valances) in all the 30 years I've owned it and has never suffered from overheating. It gets the occupants plenty warm, though.

[Colin Lindsay]

11 hours ago, NonMember said:

Apparently my GT6 must be an oddball because it's never had a shroud (or engine bay valances) in all the 30 years I've owned it and has never suffered from overheating. It gets the occupants plenty warm, though.

Mine got them shortly after I bought it, simply because everyone said the GT6 needed shrouds. I did have the radiator recored and uprated, but again have never had overheating problems.

I think it's an individual thing rather than par for the course; some cars will, some cars won't. (Some cars need a lot of lovin' and some car's don't... breaks into song again.)

[dougbgt6]

I've said it before, but that won't stop me saying it again (God! I'm turning into my father ) My shroud had sunk in the middle, being basically cardboard and was obstructing airflow rather than encouraging it, so I took it off.  It made no difference to the temperature gauge however, when I fitted the metal shroud the gauge started running half a division lower. I later fitted the side panels which made no difference at all, but they're black and have louvers, very pretty!

Doug

[Colin Lindsay]

3 hours ago, dougbgt6 said:

 I later fitted the side panels which made no difference at all, but they're black and have louvers, very pretty!

Doug

Mine hold up the cowl, so I need them, but I've also strung the wiring loom along them which keeps it up off the chassis and the associated dirt and moisture. I don't have louvres but still think they look nice.

[Nick Jones]

Don’t think what happens behind the rad (engine side panels) makes much odds, but what happens in front does.

Nick

[Colin Lindsay]

7 minutes ago, Nick Jones said:

Don’t think what happens behind the rad (engine side panels) makes much odds, but what happens in front does.

Nick

Louvres must help the hot air get out to some extent... but as Doug says they're very pretty.

[JohnD]

Ah! Louvres!   May I bore you again?

A single louvre is an improvement on a slot.   The front rim causes a vortex on the slot, where without it , the boundary layer would flow over.    The vortex energises the air on the slot, gets it moving and by Bernouille causes an approx 20% pressure difference across the slot.

But this vortex makes the boundary layer turbulent and much thicker, including some if not all of the height of the next louvre.     The vortex produced by that is correspondingly smaller,  so that the extraction effect is about a quarter of the first.  The next will be a quarter of that, until the last of a bank of louvres has almost no effect.

A bank of louvres can only be slightly more effective than a hole in the panel of the same area.   If that hole is given a backing, to make it a duct, angled at no more that 15 degrees, and the forward edge of the  hole is gioven a lip, very like a single louvre, then the surface area of the hole is energised by the vortex and becomes entirely extractive.

As an exmple, look at the nose cone of this GT40 replica:

[GT6M]

them that say its no overheating, try driving at 5K plus for a few miles in top,

or even  better OD top, then come back and say yer car dont over heat.

or even try giving it some beans in 1/2 gears for any length of time, it,ll overheat

cos plenty of revs, no much air flow  thru rad,and wide open throttles mek,n plenty of heat.

plus ne oil cooler,

 

But hosses for courses, pintl,n an potter,n  aboot,   fine for ne shrould, ne oil cooler, an half fins missing / blocked off.

[Colin Lindsay]

7 minutes ago, GT6M said:

them that say its no overheating, try driving at 5K plus for a few miles in top,

or even  better OD top, then come back and say yer car dont over heat.

or even try giving it some beans in 1/2 gears for any length of time, it,ll overheat

cos plenty of revs, no much air flow  thru rad,and wide open throttles mek,n plenty of heat.

plus ne oil cooler,

 

But hosses for courses, pintl,n an potter,n  aboot,   fine for ne shrould, ne oil cooler, an half fins missing / blocked off.

I did a couple of rallys in Summer 2018 - it was one of those the half-shaft sheared on the Mk1 which put the car off the road; I drove down and back, around 120 miles, at speeds of 60 on the main roads up to 70 on the dual carriageway; no overheating. I regularly drive to shows or events on the motorway or dual carriageway and the needle will maybe rise to halfway when stopping, but goes down again when moving - nowhere near the red and nothing that I would call overheating. I don't have an oil cooler nor an electric fan.

So: mark me down as one of those who says it's not overheating.