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More seight overheating


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Hello again,

cars back from V8 developments and running beautifully......apart from...

on the motorway, engine temp gauge (sensor is just before the rad) goes from 80 ish normal operating temp around town and spirited driving, to 65/70deg 

que 5-10mins later the needle jumping up to 110/120 and venting.

rad is mounted to the chassis, filling the nose cone and is massively efficient.

after driving from Lincoln to Macclesfield via snake pass I think the thermostat is to blame.

shuts when temp is too low and the water in the jacket then boils, que temp needle going haywire and venting as the thermostat is forced open.

any problems removing the thermostat and putting it squarely in the bin? 

Any other potential things I've missed, we reprimed and filled all hoses and rad with a leather man at Doncaster Morrisons services at 7pm last night, that seemed to help, but we avoided motorways after that point so engine temp was up anyway.

cheers in advance :)



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I believe V8's and airlocks can be a bit fickle. I guess with the speed increase , the heat increases and its unable to remove it. In your nosecone, you dont have the ducted insert. This may help to remove the heat build up. Also, the radiator , does it have the area around the nose cone blocked off, as this may have an issue with a thicker V8 rad and the air finding the easiest path and going between the nose and the rad rather than through the core.

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The running temps in general are much lower than with the polo ducted rad that was there before. 

We pulled all hoses leading from thermostat and rad and pressurised until water was squirting out from the small air valve on the top hose, so there is definitely no air lock, done that a few times before and know the signs. 

This was weird as the coolant temp would from on the motorway to 65 deg due to larger surface area on the rad then jump up too 110 etc after a few mins, hence me thinking it was the thermostat sticking closed.

The rad isn't ducted in the nose cone, that will be an addition soon but there is only 3-5mm clearance at maximum away from the nose cone. 

Cheers :)

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You can remove the stat and it will then just take ages to warm up. V8d did drill my stat to improve flow. You should ask them what exactly this is as not sure myself. 

Also check you have your vacuum advance still connected as this is sometimes removed or blanked off by v8d. Thus does affect fuel consumption and possibly timing/hot running so give it a check 

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have you fitted straight union yet from thermostat housing [ je developments sell them . ] air locks due to pipe pointing upwards . the another thing to try is i was always unsure if the header tank was big enough for that engine . and always run it on min level to allow expansion. if you dont have enough room for expansion it could be causing problem .

also temp probe is in the hottest position so will read higher . surprised the temp is dropping that low when driving unless thermostat already removed . 

if it is removed you need a restrictor  in there.  

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Cheers Pete no not got the straight JE pipe but will (maybe make my own as it's been bloddy impossible to talk to them) I'll pull apart the front end of cooling system and see if there is anything 

when in Doncaster there was the end of a thermostat that I could see in the upright hose. At this point I had a leatherman and no other options so went with the "fill it and use A roads" philosophy. (Still pulled all top hoses and filled everything individually) the leatherman is my girlfriends, many man props for her ;)

the reaction from the thermostat dial was as expected, round a town 80-90deg, long road at 50mph 60-70deg

/\ led too many 110deg overload 


Thinking to get rid of the thermostat would eliminate problems, the temp gets up too 90 deg no matter what (stock still)



cheers guys 










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Be very wary about ditching the thermostat on an engine. Unless the cooling system is set up for the non stat'd option it can cause far worse long term problems. 

The whole cooling system around the engine is designed to work against a certain level of flow/restriction. This is what helps back the coolant in properly around all the complex cavities and passages. Removing key restrictions like the thermostat, without doing anything to reinstate the restrictions can result in localized boiling around cylinder heads, and ultimately the formation of micro bubbles and tiny pockets of gas, causing localized hot spots in the combustion chambers. Trouble is, because they re so localised the overall coolant temp seems ok measured by the gauge, so you don't do anything and it just continues like a little ticking time bomb.

if you do remove the thermostat element itself, then strictly speaking you should, as Pete said, fit a restrictor to limit the flow to what it was with the stat in place. But then there's not really any advantage to removing the stat.

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when i had it  it had thermostat and i drilled a hole at the top . this was supposed to help any air locks and help the cooling .if you remove the thermostat and the whole system gets up to temperature and you then get stuck in traffic the car will soon boil over . but saying that in this weather it should struggle to get up to temp. if not you must still have a air lock.


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Ok im a bit confused

Timeline:  car runs from dead cold, coolant temp gets too 90/100, electronic fan kicks in (it's set up the lowest values but still kicks in higher than I'd want)

tenp sensor/ dial relays 90deg this does reduce to 80 deg after fan activation.

fully striped and primed all hoses to eliminate all possible air locks, this is not the cause I can guarantee.  


Now it's rock solid when driving at 30-50mph in traffic (80/85deg) or anything.

Go toward the motorway and 60-70mph, the temp (on the dash) reports 60/65 deg (more air mass moving over the surface area of the rad makes the temp plummet) for ages until it boils over suddenly. 

Does that sound like a thermostat sticking?

looking like removing the thermostat is a bad idea 

  but lost in this if I'm honest. 


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Removing the stat fully may be a bad long term solution, but do test that it's working ok.

Where in the cooling circuit is the stat, in the hot outlet side of the engine, prior to the rad, or in the cool return side, between pump and rad. Also, do you have a cold start by pass circuit?

it sounds like the stat is seeing a cold enough temp to shut, and then for some reason, not opening again, when the temperature in the engine block rises.

I'd rule out a faulty stat first. Then I'd be very tempted to do a motorway test run. But just before pulling on, blank off part of the rad, so that it won't over cool, see if the temperature is more stable and doesn't get down so low, and then spike afterwards.

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The stat is in the hot top hose running to the radiator from the engine, the sensor is in line with that just before the rad.

Don't think I have a cold bypass, but I don't know what this would look like so not sure.

good idea with blanking off the rad, it would fit as to get engine temp back up to normal I slowed to 40mph on the motorway and the needle returned to 80deg happily (on the last run making me think eureka!) 

what  would be a long term solution to this problem? 



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seems strange to me that engine gets up to temp but drops when you are running on the road is   below what i would expect . the thermostat should keep engine at the thermostat temp .it should not be dropping below its temp  that is not  the idea of it . you need to get a cheap heat gun and get readings off the pipework to see whats happening.


i take it you have moved the temp probe because it was in the inlet manifold before . if its in the pipework after the thermostat it wont be reading engine temp. but temp of water in top hose.



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Ok I've got a probe sensor for temp, can now take the nose cone off fully and see what's occurring at all points of the cooling system, I'll do that when I'm next with the car. 

Re the sensor is it the probe with the long curly wire that connects to the fan thermostat switch? Or is that just for the fan, was assuming it was both. 

Might buy a new thermostat anyway to rule that out of the equation.

what are the problems with over cooling an engine?

Actually a quick google has the answer ;) 

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