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GT6 running hot on idle


hughestill
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Hi all,

 

My GT6 is running hot - not an unusual cry from the forum I'm aware. Just wondering if anyone can suggest most likely cause? Setup is as follows:

 

Newly rebuilt engine (about 350 miles since rebuild)

Original (but re-cored) GT6 rad

Radiator & engine shrouds

Original mechanical fan

Coolant:water mix 20:80

15lb rad cap

No front number plate blocking the air flow to the radiator

Mechanical (capillary) temperature gauge (backed up by Racetech temperature strips on the head)

Standard thermostat

 

The car seems to be OK while on the move, but if I leave it idling @ around 1000rpm on the drive for 15-20 mins it hits the top of the (mechanical) gauge.

 

I've also verified the temp gauge by using Racetech self adhesive temperature strips on the front of the head, and it suggests temp gets up to 230F (110C).

 

I've no evidence of the coolant boiling, nothing in the catch tank - but then I wouldn't expect it to boil until about 125C with the combination of coolant mix and rad cap.

 

There's no apparent loss of coolant from the system and the oil looks..well..oily, so I'm ruling out HG failure.

 

It's been like this from the moment the engine was started after the rebuild, so it's a constant feature/issue.

 

At the moment, my list of possibles is:

- thermostat: was new on installation, and I THINK I checked it before I put it in, but possible failure?

- head/block/heater matrix silted up: but, if that's the case, why does it run cooler (between 190F/88C and 212F/100C) when moving? There can't be enough air cooling effect to bring down the temp that significantly, surely?

 

That's about it. Sat here scratching my head, so any suggestions welcome.

 

Thanks,

Hugh

 

(I do plan to retest using the self adhesive strips on the thermostat housing, as I'm aware the head is the hottest part of the engine, can anyone advise what is an acceptable temperature range for either/both of those points?)

 

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Can you "feel" the thermostat opening? It may be worth changing it over, and I would be fitting an 82degree version.

Also check the timing, too far retarded can/will cause overheating. But likely to be all the time.

New engines tend to run hot, it shoudl improve with mileage as it loosens up.

A cheap digital infrared thermometer (under a fiver on ebay) would help locate any cool spots in the rad, so worth a try?

 

just throwing some ideas out there. Somepeople seem to get a GT6 that runs cool, most seem to run a bit hot, even like yours all "new". Very odd really!

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Thanks Clive. I've just taken the old one out, which was an 82, and I think it may have been seized - I put it in a pan of boiling water and it took about 30 seconds to open, and then did so quite suddenly. Now, while it moves more freely than it used to, it's still very stiff compared to the new 75 degree one I've bought. 

 

I'll get the new one in and report back.

 

Thanks again,

Hugh

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"There can't be enough air cooling effect to bring down the temp that significantly, surely?"

 

You only need the fan when stationary or in slow moving traffic. I used to have a Peugeot 306, the radiator temperature sensing died so I rigged up a toggle switch on the dash to turn the fans on. The fans only ever needed to be on when sat in traffic for 20+ minutes. I regularly drove 400 miles up to Scotland and traffic jams aside the fans were never needed.

 

The engine's been rebuilt but have the block waterways been flushed out? Worth a try!

 

Doug

 

PS Don't call me Shirley! :lol:

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Indeed. My Spit (zetec engine, VW rad and fan) had the bearing seize in the electric fan on the first day of the 10CR last year. We managed well over 3000 miles without it, though I got very good at "heat management" ie on the motorways, let the engine over-run for as long as possible before stops, heater fan on (and it was very warm weather anyway) and so on.

I could complain about the fan, but it was date-stamped 1982! Not bad. I replaced it with another SH fan as a direc swap, reckoning it would outlast the copycat cheapo ones that are sold as replacements....next time it will be a spal though.

 

I am waffling. GT6's are special in their requirements with heat. An electric fan would be a big temptation to me, even as an extra on the front of the rad.....but that has some drawbacks.

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Thanks all, an electric fan is already on my shopping list, so we'll see where today's experiments end up.

 

Pete - you've confused me now. I was under the impression a richer mix would lead to a cooler engine, as the additional fuel in the mix makes the burn temperature lower. I can see why this would be a good thing generally for running in, as it would reduce the power output and protect components, but I'm missing the connection between thermostat opening temp and fuel mix.

 

Thanks

Hugh (fully prepped for a chemistry/physics lecture.. :-) )

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cold engines need a higher fuel mix ratio  eg its progressive from being cold needs a choke to being very hot needs to be leaner

 

in the early years of emissions controls  engine  thermostats went commonly up to 88c so you could lean the ratio down more  than 82c   to run correctly with a 75c you really need it to be richer 

 

Im no chemist but did run a  truck emission dept for petrol emission  and diesel smoke  tests in the 70-90s 

 

Pete

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  • 2 weeks later...

My GT6 with 13lb rad cap will perform in a similar manner. I got caught in a bad traffic queue a few weeks ago: engine was up to temperature when I met the back of the queue. Over the next 35-40 min we crept forward, with me eyeing the temperature gauge. It moved from just below half (its usual position) to around 3/4 quite quickly, then slowly moved up to just below the red where it sat for 10 minutes before I cleared the queue and got onto the A1. Within a mile of normal flowing traffic the gauge was reading its usual mark again. I flushed my block through when I changed the rad to an updated core one last year.

 

Gully

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The first step in any investigation of a "hot" engine should be, is it really hot?

The gauge is reliable, but the sensor is not, nor is the "voltage stabiliser".

Failure of the last will give a "hot" reading, and the sensor can fail in a several ways.

 

Check that the VS is delivering either 0V-12V-0V- as it should (averaging 10V if you have a suitable voltmeter), or a steady 10V if you have a modern transtorised one.

Buy an infrared thermometer 'gun' (less than £30 these days) and measure the temperature in the hoses and water pump housing.

Check the reading against that known temperature, or else by removing the sensor and setting it up on the bench in a water bath on a camp stove.

 

  Bench set up

 

post-139-0-65453200-1476614113_thumb.jpg

 

 

What the response should be

 

post-139-0-80702200-1476614124_thumb.jpg

 

 

 

What it shouldn't be

 

post-139-0-73793500-1476614139_thumb.jpg

 

 

John

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The first step in any investigation of a "hot" engine should be, is it really hot?

The gauge is reliable, but the sensor is not, nor is the "voltage stabiliser".

Failure of the last will give a "hot" reading, and the sensor can fail in a several ways.

 

Check that the VS is delivering either 0V-12V-0V- as it should (averaging 10V if you have a suitable voltmeter), or a steady 10V if you have a modern transtorised one.

Buy an infrared thermometer 'gun' (less than £30 these days) and measure the temperature in the hoses and water pump housing.

Check the reading against that known temperature, or else by removing the sensor and setting it up on the bench in a water bath on a camp stove.

 

  Bench set up

 

attachicon.gifTemp gauge test setup.jpg

 

 

What the response should be

 

attachicon.gifNew temp sensor response.jpg

 

 

 

What it shouldn't be

 

attachicon.gifTemp.sensor responses.jpg

 

 

John

Hi John,

 

I've got a mechanical temperature gauge, so if I understand it correctly the voltage stabiliser is eliminated from the equation? Also as per original post, I've cross checked with the self adhesive temperature strips - they obviously don't give a specific reading but indicate if a certain temperature range has been reached. Even allowing for some margin of error I think 230 degrees on the strip and the gauge suggests definite hot running issue. However, all that said, I have ordered an IR temperature gun so I can record more exact readings!

 

Having had the block waterways flushed, and still having a problem, I'm narrowing it down to the following:

- blocked heater matrix (looking at that this morning).

- radiator issue (would be disappointed as I had it re-cored with an uprated core and pressure tested before rebuild).

 

Couple of questions on this:

- will it/should it help if I bypass the heater matrix? I've seen a few threads on various forums suggesting it won't cause any problems, and in some cases resolves an overheating problem, but I can't see how it's any different from just closing the heater valve?

- clutching at straws, but is it possible to fit a GT6 head gasket upside down, thus blocking water channels? From what I can see, it's pretty much symmetrical so my feeling is not (I have a non-recessed block). If it IS possible, what other symptoms might I expect to see?

 

Also - how hot is REALLY too hot? When I'm looking at temps in the head/hoses/water pump housing, at what point should I become concerned?

 

Thanks to everyone for their replies and suggestions!

 

Cheers,

Hugh

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the heater circuit is a bypass , when you close the valve it takes a shortcut back to the pump ,think youre correct it wont make any difference

 

has the thermostat got the air bleed jiggle pin in its rim, if not drill a 3mm hole in the rim to let air out when stat is closed

 

very hard to test a flow in a rad you need a big pipe and a large  header to give the flow ability of the core, a hose is just tickling a few tubes 

and with no flow data what does one expect.  there's nothing to validate to.

 

is the stat working if its 82c then expect output hose temp to be similar,  the stat opens and closes all the time as cold coolant is allowed back in from the rad .

 

the bottom hose should be a good bit cooler as the rad does its job, but  how much cooler ?????  where's any data ???   so the stat modulates all the time 

if you can run with the cap off you can see the ebb and flow  across the top of the rad as it opens/closes every few seconds

 

 

Adli or  was it Lidl were doing a infra red gun for about £12 last week 

 

believe you are right the std gasket fits anyway up

 

Pete

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Hi Pete,

 

Thanks, existing thermostat (the slightly lazy one I replaced) had a jiggle pin, new one didn't but I had drilled the hole before I fitted it.

 

Got my infrared thermometer today - weather and time have run out today but hopefully I'll share a few readings tomorrow.....

 

Cheers,

Hugh

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Doug

I have one fitted as I have a dual oil pressure and temperature gauge. It works on a capillary action so heating the sender expands and pushes a fluid which in turn moves tha gauge. The only issue with them is that you can't take the capillary apart so to remove the gauge you also have to take out the sender and connecting tube/pipe

 

 

Aidan

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Better/more usually described as capillary (as Aiden says)

http://www.ebay.co.uk/itm/VDO-TEMPERATURE-GAUGE-INC-4-16-VAT-120-C-52mm-CAPILLARY-180-00-036-023-/191974199206?hash=item2cb28dcfa6:g:U7UAAOSwepZXRgrN

 

or dual gauge

http://www.ebay.co.uk/itm/DUAL-Oil-Pressure-Water-Temp-Gauge-KIT-will-suit-many-1950-70s-Classic-Cars-/331070985885?hash=item4d155e569d:g:5AkAAOxygj5Sjpju 

 

The REALLY handy thingis that you an check the calibration of these gauges by putting the bulb in the kettle when you make a cuppa, and see exactly where 100 degrees is. And if you want to, and have a thermometer, where other known temps are too. The gauge should be linear.

 

And the number of times I have seen those gauges for sale at autojumbles with the capillary tube cut off. The sellers imply (innocently?) that a new tube can just be fitted. They fail to mention it has to bedone by a specialist, last time I checked about £40, but I bet more now.....

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Most chemists sell thermometers that go up to 40C, because if your body temp gets any higher, it will soon cool down again, 'coz you is dead!

 

An oven thermometer reading up to 200C would be more useful, but they tend to be designed to be stuck into meat or pies, so would struggle with the temp of the surface of a hose, or tyre for that matter.

 

John

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So, it may just be a case of "I own a GT6".... I'd welcome a bit of a sanity check on the following:

 

Having bypassed the heater matrix with one of those flexi copper tap connectors, I let the car warm up to 190F/(88C on the drive, then took it out for a run. Maintains temperature at around 160F/71C on a 20-30 min run from warm. At higher speed, temp drops even more which makes me think the airflow over the radiator is good, and the core of the radiator is good - does that make sense?

 

On returning home, left the car on the drive for 10 mins (temp just below 160F/71C on arrival), and it heated up over the course of that time to the top of the gauge (230F/110C). I checked all the temperatures around the rad with an infrared heat gun and confirmed alloy thermostat housing temp at 229F, top hose temperature around 215F/102C, bottom hose temperature around 205F/96C. Initially I thought the differential between top and bottom hoses was way too low but then remembered the airflow over the rad was minimal to non-existent. Anyone think that differential is still too low?

 

My final conclusions at present are:

- I own a GT6 where cooling is marginal at best. 

- I need to look at the standard crankshaft fan to make sure it's fitted the correct way round

- I need to invest in an electric fan (any recommendations for optimum/best?)

- I need to replace the heater matrix (grr..)

 

Anyone think I should be seriously concerned about anything?

 

Cheers,

Hugh

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Do you have the fairings that direct the airflow from the intake to the radiator matrix, without it leaking round the sides?

I have heard of GT6 owners who found they are essential.

 

But then your temp was fine while running - now you're just stressing about the heat while the engine is stationary!    The coolant "thermo-siphons" and radiates from the radiator, even without air flow.  If that worries you, then fit an electric fan with with a timer to keep in running for a fixed period after you switch off.  Many moderns do this, but of course you rely n the battery for this.

 

John

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Do you have the fairings that direct the airflow from the intake to the radiator matrix, without it leaking round the sides?

I have heard of GT6 owners who found they are essential.

 

But then your temp was fine while running - now you're just stressing about the heat while the engine is stationary!    The coolant "thermo-siphons" and radiates from the radiator, even without air flow.  If that worries you, then fit an electric fan with with a timer to keep in running for a fixed period after you switch off.  Many moderns do this, but of course you rely n the battery for this.

 

John

Thanks John - after reading this, I re-read my post and what I should have said was "On returning home, left the car IDLING on the drive for 10 mins".

 

I'm not so worried about the heat while the engine has stopped, it's the potential for overheating in traffic that concerns me - but, I think it looks like an electric fan should do the trick for that.

 

I've been trying to work out what spec fan produces a comparable airflow to that generated by travelling at 40mph but my maths isn't up to it, it would appear..  

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what engine fan is currently fitted??

 

all our cars prefer good air movement under the bonnet when in traffic .idling etc, to keep the under bonnet ambient temp down. an engine fan does this where as electric comes on to what  its set , the engine driven is pulling air all the time ...better 

 

there are changes to fans over the years from 2  to 7 blades metal to plastic   whats yours called ???

 

 

 

Pete

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