overheating

[f100stepside]

Hi can anyone help me with my overheating problem.Had my MK 2 for almost 30 years and no problems,last year was running hot so i have removed the engine water plugs for the first time and gave it a good flush including removing the rad and flushing it out. I have refilled the cooling system slowly, heater in the on position jacked up the front pass side to allow the water to fill the system fully,the heater is blowing hot air ok. The water pump seems to be ok when reved up can see water moving.Could it be as simple as the thermostat seems unlikly. Has anybody got some advice please. jonathon

[Ian Durrant]

Yes it could easily be something as simple as thermostat. They fail in various ways, stuck open, stuck shut or stuck partially open.So long as you don't have problems getting the thermostat housing bolts out, then its a simple job to whip it out and test it in a saucepan of water. Heat the water up and the stat should gradually open until its fully open. Of course if you find it's partially open when you take it out, the saucepan is unnecessary.

[Ian F]

Jonathan

Agree with all Ian has said, I've just had to re-fit an old thermostat because a new one (same temp.) caused the car to run much hotter. Tested both, plus a new 74 deg one I bought, and the only one working at the correct(ish) temp. Was the original. Refitted it and back to normal.

one other question, when you flushed it, I assume you removed block drain plugs as well? I was always told never to assume!

ian F

[uzbek]

If the 'stat is not opening the top rad hose will not be hot when the car is up to temp. Easy to check before taking out the thermostat.

[richardthestag]

is it overheating? what happens?

The reason I ask, my gauge read hot i.e. RED, engine felt normal. Problem resolved by reattaching the voltage regulator earth on the back of the speedo The maxed out fuel gauge when I knew it was nearer empty was the clue.

then a few more years before that I had a similar problem yet the regulator was attached. turned out to be a rogue temp sender. replaced one with black insulation (and not white) got things back to normal.

even more years ago Car ran hot at speed on the motorway. turned out I had the wrong thermostat fitted. my inlet manifold needed the extra foot on it.

Most recently - last year - the cooling system spat water out past the pressure cap while running. dreaded HGF caused the combustion gasses to over pressurise the cooling system.

None of the above caused actual overheating.

[f100stepside]

Hi thanks for the reply's.Last year i had a problem with the temp sender gauge on the engine block,it was going straight into the red and doing other odd things,replaced it and it seems to be working ok.The gauge is between half and red when driving and going into the red when standing still,getting very hot and exiting via the expansion bottle overflow pipe.I did remove the water plugs on the enging block before flushing.Drivers side hard to get to and gave me a good soaking! pass side even harder to reach,took the plug out but no water!, poked it with a screwdriver and another soaking!. I am planning on changing the thermostat today and i will let you all know the result. If anyone has any other info just let me know.
Thanks Jonathon

[Marco Polo]

Sounds like the thermostat to me, if you had to clear one drain hole it may be worth giving the whole cooling system, including the rad and heater matrix, another flush too. I've drained and refilled my cooling system every two years for the past fourteen years and I'm still getting gritty sediment of some sort out of it, however it does appear to get less and less every time, last time was less than 1/4 teaspoon full, first time was two tablespoons of casting sand.
regards,
Raoul

[f100stepside]

Just taken out the thermostat, very rusty 82 deg type checked it and it's not working. Just put new one in got enginge up to temp,top hose is hot can hold it but not too tightly. Temp gauge is just over half way ran it for 15 mins and it stayed about the same temp,but i still think this is to hot,as iv'e had it for years and it's always run between a quarter and half.

[StagnJag]

Hiya,

No one has mentioned the Viscous coupling yet, is that showing any signs that it is on hte way out? It should have no forward and back play and shouldn't spin freely.

I am a bit concernd that you say the thermostat is Rusty, the coolant should prevent any major corrosion. Sorry to ask this, but are you using antifreeze? You should have aomewhere between 30% and 50% all year round to prevent corrosion. (I run 30%).

Regards

Dave

[f100stepside]

just been out for a test run,started off ok the got hotter and hotter.Had a good look with a powerful inspection light and there's a small hole in the top of the rad!!!.Original Mk 2 rad, so do i have it repaired or go for a super gill?.Has anyone got some experience with the uprated rad? do they fit as a straight foward replacement? which one is best to go for?.
Thank Jonathon

[f100stepside]

Hi yes i do run a good strong antifreeze solution,but have been messing around with it for a couple of months flushing and so forth,so i just used water.I have just checked the coupling and it seems ok no play or movement, thank's for the advice.
Jonathon

[wilf]

No reason not to have your existing rad re-cored.

[DJT]

No reason not to have your existing rad re-cored.

+1

[uzbek]

Can I also suggest you get a cheap IR thermometer. Then you can check that what you see on the gauge is actually a true reading by taking measurements beside the sender. Turned out mine was spot on but many are not.

[Paul Roberts]

Jonathon,

With everything in good order???, you would expect the working engine coolant to be in the range of 87 to 97 degrees C.

Assuming a nominal internal water system pressure of 12-16 PSI (radiator cap dependant) your coolant will begin to boil at around 115/120 degrees C. (antifreeze mix dependant).

The controlled flow of coolant is key to keeping everything working properly. No flow, or restricted waterways, means localised hot-spots and trouble. Too much flow prevents the heat transfer from the hot bits of the metals to the coolant fluid (not enough time.) The same principle applies to the radiator which transfers its' heat to the cooler air flowing over/through it.

The basic equation (of heat) is; heat lost = heat gained. It's a one way street; the cooler bit absorbs the heat from the hotter bit (it only ever flows from hot to cold.) Time and temperature differentials are also fundamental factors.

(There is a forth factor, "Entropy" - which is usually only referred to in cosmic sciences - that tells us the universe, ultimately, wants everything to be at the same temperature; but I don't think that has any real bearing on us Stagists.... )

The various ways heat can be transferred can be complex but, notionally, it moves by any of three ways; conduction (through solids), convection (through fluids) and radiation (through space).

Your engine is, effectively, trying to transfer its' internal heat to the surrounding air outside by all three methods. With the Stag engine it's invariably the fluid flow bit that causes the problems.

So, in conclusion, make sure all the waterways are clear. But you already knew that eh...

TBO