4 hours ago, D.FYLAKTOS said:

Υour thermoswitch is new or old?

Temperature range? Mine now is 80-85 'C although i have tested 75-80 'C, 85-90 'C and 87-92 'C

The thermostat switch has got 84-91 stamped on the side. I know it works and at the moment I’m happy with how it’s performing. It comes on when the needle is horizontal or around 100 degrees

@nta16 hi mate, my intention with doing the system flush was to open up any small passage ways that could be restricting the coolants flow. I think the flow is good as I’m getting a good return at the header tank.

Checking what I’ve fitted the thermostat housing is correct to LLLparts though mine according to my order has an 80 degree thermostat rather than 87 degree one quoted.

The water pump is a Quinton Hazell Water Pump QCP3157 which was bought as part of a kit . When doing a search it says 8th the correct one for the car.

The head gasket kit I’m still trying to track down what I bought from GSF.

Timing I will check again but isn’t managed by the ECU? Plugs are what came with the car (I’ll check their correct) air filter, oil filter and oil 5/30 are all new.

Brakes are free and release well after being applied.

When the car is sat on the drive the temp will climb slowly towards 100 degrees, the fan kicks in and will bring it back down to 90.

Over the last couple of days I’ve been vacuum filling the system though it only seems to take between 3-4 litres of coolant at a time. When applying the vacuum it holds rock solid and doesn’t budge. I also pressure tested the system and it only dropped 2 psi in 3hrs. This suggests to me that the head gasket has a good seal but I will do a leak down test this week.

I have today tried to burp the car by jacking it up from side to side while running it up and applying revs. I did notice that there wasn’t a great build up of pressure in the system and I was able to remove the cap without any loss of fluid.

I’m now starting to think that my coolant hoses are too soft and are not supporting the system when pressure should be building.

2 hours ago, Rsedmonds said:

It comes on when the needle is horizontal or around 100 degrees

Since we have hot climate here and to prevent head gasket failure (overheat) i have installed a 80-85 'C.

58 minutes ago, Rsedmonds said:

I did notice that there wasn’t a great build up of pressure in the system and I was able to remove the cap without any loss of fluid.

So no excessive air (bubbles) inside your system.

As for head gasket test:

https://www.briskoda.net/forums/topic/head gasket test

I don't know these cars (pick-ups) or engines at all, so you might have the Polo 1.6 engine of the time or 1.6 original to Felicia of the time and I've no idea how much their ECUs and set up would vary, I'm more used to carbs, an electronic distributor and indicator flasher unit are my electronic excursions away from basically 1950s designs, even if build in 1960s and 70s. I do remember seeing the bright yellow Fun pick-ups when they first came out but never being a VW fan never notice the VW pick-ups, that are so fashionable now.

Cooling basics remain the same, even on the more annoying later more complex, aren't we German's clever, designs. I'm not sure the Felicias or Polos of last century had been taken to much of that annoyance and complexity but I could well be wrong.

System flush is a good idea, my thinking with backflush was to help not to clog or partially clog any small water ways with nearby or transited debris also helped by breaking the system down by taking it apart to zones with openings that give you more direct sight and access to apertures of flushing and/or scraping out. But no matter what you do you can only get so far or do so much unless you completely strip everything down. Same other fluid changes, things like oil changes always leave a residue to mix in with the fresh new fluid introduced. The idea is to reduce the residue as much as is reasonably possible so that the residue has the least diluting effect of the fresh new fluid.

If you have good flow and no bits turning up anywhere in the fresh new coolant then that is fair enough.

Air locks can be an issue but I have always found following the Driver's Handbook method and no other is good and no need for all the other things some people do but I am very slow and careful, checking the book despite having unfortunately to do partial and full refills far to many times. I even got away with a full coolant change on my wife's 2015 Fabia without the use of vacuum or scan tool despite taking ages to remove two annoying self sprung hose clips in a very awkward place to get even the correct tool on let alone the non-correct tools I had to hand (only one instance of why I don't like the German car way of doing things). There are simple kits that help filling old cars to avoid air locks.

The pressure in the coolant system is about higher temperatures, you won't achieve it with the pressure cap off so I doubt soft expanded hoses will make much odds to your current issue, if they split and burst that's a whole new ball game.

I forget now who owns the QH brand and where the parts are made as it's been a while since I researched parts for my car but the others here will be able to tell from a photo if the QH water pump construction looks the same as original water pumps.

Of course the QH pump does have to be the correct model to purpose and there may be variants, a quicker pump isn't necessarily a good thing, pump needs to be correct for application. If you have done your research and checked and cross referenced the information with good reliable sources of information then that is fine.

The others would know better than I about acceptable pressure losses but it has made me think of pressure cap which I think we have covered before but if not that's another thing to check - blue(?) or yellow(?) screw on cap, doubt it's a steel bayonet which used to last for very many years but more modern one didn't last as long (a service item for some).

Plugs are more of a general thing, but if they were in the engine when you got it you don't know their history and you would certainly check them for being correct and in good condition, and colour for engine running condition. Fake plugs have been about, if too bad you would have misfires probably.

The ECU sorts out the running but has no direct control on mechanical parts so they need to be in good order other wise everything is compensation for the issue and may not be fully capable.

As said many (many) times brakes are important relatively engine is NOT, so I'd not expect the brakes to be bad but drums can drag and you might not notice too much unless you put your hand on the wheel(s) I only think of such things as a possible contributory factor rather than the actual cause as I'd hope you'd notice if the brakes were that bad they caused the engine to get warm - but I don't know (or have forgot) if you have ever driven a Felica in reasonable condition or old cars to know what and how they should be. I've meet owners who have thought "old cars are like that" for stuff that was actually something faulty or lack of knowledge about the proper servicing, maintenance and repairs plus lack of proper driving of the vehicles over enough miles and conditions and circumstances. Plenty new to old cars or that model but also some long term and/or older owners that should have know better. The old "they all do that", often, yes when they're not kept well or driven properly.

Temperature building whilst parked might be an underlining issues or if that takes a very long time a normal thing, others would know better than me but the running above what it normally should when driven again is an issue that needs resolving.

Often going back over and checking everything (again) with someone else with you - the very basics first, engine set up, new parts fitted, ideas of what to check, etc. etc. can often turn up something previously missed or new ideas or solution. Number of times I or someone else have thought they'd already checked something they hadn't or dismissed something or checking or rechecking something because they think or have been told "it won't be that" to discover they should have checked or rechecked or it was that after all.

A mate, unlike me who knows about mechanics and worked on lots of vehicles, and I was doing something or other on the engine of my car and he reconnected the HT leads, only 4 of them you can't go wrong, and soon after starting the engine I ask him "why's that exhaust header getting hot?". He'd mixed up two leads yet the engine didn't sound like it was running out of order. We laughed, I couldn't say anything as one time I helped him reconnect his suspension arms to speed things up so he could to for a test run, very unusually I finished first, looked at him still spanning up and asked "why have you put that over that?" - I had to undo my side and redo it the correct way, so much for saving him time.

The best and worst of us regardless of lots of experience, or lack of, can make schoolgirl errors.

Good luck.

2 hours ago, Rsedmonds said:

though mine according to my order has an 80 degree thermostat rather than 87 degree one quoted.

80 will open sooner and close later than 87 so until and when the coolant temperature is above the fully open 80 then the engine will be kept cooler, once passed the fully open temperature of a stat the stat can do no more.

15 hours ago, Rsedmonds said:

has an 80 degree thermostat rather than 87 degree one quoted.

This is not good, will take from the engine precious temperature that it needs to reach the level to work properly.

The 80 'C is for Middle East, in our countries at Winter the heat will take lot of time to be ready for the cabin, the sensor will pass that info to the ECU and the ratio fuel-air would be richer.

At the moment the 80 instead of 87 may actually help a little with the running warm and anyway as I put once the coolant is above the fully open temperature of the 80 or 87 stat the stat is out of the game until the coolant temperature drops again to the stat's opening/closing range of operation. Plus the cabin heat was quoted as 50c(?) that's very hot considering the vehicle is in the UK in early March, even on a rare very warm early March day.

Probably not so possible with such a modern old car but a con for selling an older vehicle with cooling issue(s) for whatever reason(s) was to remove the stat to prevent too much build up of heat when selling the vehicle.

20 hours ago, nta16 said:

Plus the cabin heat was quoted as 50c(?)

80 'C has the sauna.

I have measured 47 'C in mine (the car was outside under the hot summer sun) and till i open both windows and start rolling the car the situation was awful.

On 08/03/2026 at 19:46, Rsedmonds said:

I did notice that there wasn’t a great build up of pressure in the system and I was able to remove the cap without any loss of fluid.

Was this with the engine warmed up? The cap has built-in pressure valve, so if it's faulty, it won't build up pressure. The cooling system won't work properly without pressure.

6 hours ago, Papez said:

Was this with the engine warmed up? The cap has built-in pressure valve, so if it's faulty, it won't build up pressure. The cooling system won't work properly without pressure.

I’ve tested the cap and it blows off between 1-1.5 bar which is correct.

I’ve going back to scratch and stripping the whole thing down. I’ve ordered replacement pipes, not moulded but the correct bore so thought the run might be longer the flow should be as per spec.

I’m also going to order a heater matrix (even without feedback from my other post) and then everything in the cooling system will have been replaced.

12 minutes ago, Rsedmonds said:

I’m also going to order a heater matrix (even without feedback from my other post) and then everything in the cooling system will have been replaced.

I would check with others first as a new heater matrix might be poor (crap or abysmal) quality - or might not. But this is an expensive way of doing things, firing off the parts-cannon, sure when new parts are inexpensive AND reliable it can save time and hassle. But sometimes a new modern made part may not solve the issue and can at the time or later cause its own issue(s) so be careful.

If you are taking things apart do this slowly and fully inspect the parts and what it's fitted to and that the part can and does fully operate as it should. Look for anything that is present that should be or shouldn't be.

I left some blueroll in a stat housing and that created some funny temperature reading and operation that I wouldn't have got to other than looking at what I had done during the work I'd done. And a mate had a used motorbike where it had to be "serviced" at the place of sale for the x-months warranty, this involved travelling, time and hassle for my mate but he done it, on the way back it wasn't running right - the mechanic had left a rag in the engine so the engine had to be replaced by them with a recon engine at their expense. Mistakes happen and Sod's Law often applies.

Good luck.

Edited 10 March10 Mar by nta16

Another thought (a rare event), as I don't know the heater plumbing arrangement I'm not sure how the heater matrix would be a cause, partial cause or contributory cause to your issue, but how about rather than ordering a new matrix first try bypassing the heater matrix to take it out of the equation and see if that makes any difference.

@nta16 I agree the parts cannon is not the way to go and all parts so far fitted have been to replace damaged parts or recommended during a service. But by replacing the parts for the reasons stated now means that the only parts not changed is the heater matrix and pipe work. I can see that my lower radiator hose has gone soft so if not replaced soon will soon split and the other hoses fitted don’t fit correctly.

I’ve removed my heater matrix today and other then the contents coming out of the box resembling and saw mill it the matrix only holds 200mls of water and checking the internet I’m see figure of between 300-500ml as an average for standard heater matrix’s to hold. if I do end up replacing it which I’m starting to doubt whether it needs to be replaced.

But, once I’ve rebuilt the cooling system it rules it out which then leaves me the question of what else it could be?

10 minutes ago, nta16 said:

Another thought (a rare event), as I don't know the heater plumbing arrangement I'm not sure how the heater matrix would be a cause, partial cause or contributory cause to your issue, but how about rather than ordering a new matrix first try bypassing the heater matrix to take it out of the equation and see if that makes any difference.

I did but nothing changed

Certainly if doing work on a part, system or component then that is a good time to replace as required, sometimes with better than already fitted but bear in mind many/some "upgrades" and "improvement" aren't. Replacing a very dodgy hose is a priority.

5 minutes ago, Rsedmonds said:

I’ve removed my heater matrix today and other then the contents coming out of the box resembling and saw mill

Now you see why I recommend removing or at least separately cleaning, flushing, back-flushing and flushing again the engine block, radiator and matrix directly individually. The amount of debris that can be in old car's cooling / heating systems can surprise many even after they have done regular coolant changes.

11 minutes ago, Rsedmonds said:

the matrix only holds 200mls of water and checking the internet I’m see figure of between 300-500ml as an average for standard heater matrix’s to hold.

Don't go by the internet, ask the expert owners here. What did that average refer to and include, old vehicles, new vehicles, Yank tanks, sensible smaller cars, etc., ect.. Also did you take measurements of the matrix or photos (with something to give some sort of scale) as you may be assuming the heater matrix in your pick-up is original or correct to application when it isn't. It might be correct, it might not, never assume with a vehicle you personally don't know the full hands-on history of.

If it's not the "water" cooling system then that leaves all the other stuff previously listed (IIRC HGF was covered previously so if you have a test kit use it again just in case before tearing stuff down perhaps).

Keep going you will get there and when you do it will be burnt into your memory, well until you get too old anyway. 🙃

Have you tried removing the thermostat valve and run without it? Just to make sure it works properly and doesn't limit flow. I know it's new, but it's been proven numerous times that "new doesn't mean good"

3 hours ago, Papez said:

Have you tried removing the thermostat valve and run without it? Just to make sure it works properly and doesn't limit flow. I know it's new, but it's been proven numerous times that "new doesn't mean good"

@Papez hi, yes is the short answer. When I put the coolant system flush in I removed the thermostat and ran it up to (and passed temp) I then flushed it twice and both times it went higher than 90 degrees.

21 hours ago, Rsedmonds said:

@Papez hi, yes is the short answer. When I put the coolant system flush in I removed the thermostat and ran it up to (and passed temp) I then flushed it twice and both times it went higher than 90 degrees.

Then there must be an issue with flow somewhere. Without thermostat, it shouldn't even warm up.

But iirc, you said that heater worked well?

@Papez theres an issue definitely but where I don’t know. When I got the car it had a blown head gasket so it’s had an issue since day one (for me anyway). Obviously the HG has been changed and as part of the rebuild it’s had a new water pump as part of the cam belt change, the pipe from the pump to thermostat housing changed as the end was broken, and the thermostat housing has been changed as the threads were stripped. So with all those things changed it’s still overheating. I went to change to the diesel rad but backed out due to fitment issues but exchanged that for the correct size for the 1.6.

Now clutching at straws and the only things not changed are the hoses and the heater matrix. I’ve removed the heater matrix and with the help of others determined that it’s holding the correct amount of fluid and so has been refitted. I have noticed that the hoses to the heater matrix are incorrect and stretched around the airbox. Also the thermostat to lower radiator pipe is super soft and semi collapsed (but this has only show it’s self since I’ve started using a vacuum fill) so a 2 meters of 32mm pipe and 3m of 19mm pipe have been ordered and will get fitted this weekend.

I have tested the radiator cap pumping in just under 2 bar into the header tank and it released that pressure.

When it’s all back together and if it overheats still the issue has got to lie elsewhere but where or what I’m lost.

Right, I've had to take some time away from this as I’m close to rolling it off a cliff 🤬.

Changed the pipes and though it’s slightly improved thing it’s not change the overall issue of it over heating.

After running the truck for over 20 minutes I can see moisture on top of the pistons and I’m not sure whether it’s oil, water or just condensation. What I do know and is the reason for my post is that I have (and always did have) compression across all 4 cylinder of 16 bar.

So my question is, Is 16 bar within range and an acceptable pressure or am I way to high and could this be a possible root cause of my overheating?

https://www.briskoda.net/forums/topic/369187-13l-engine-compression-tolerance/

"10 - 15 bar compression for injection engines"

Skoda Felicia II 1.6 (75 Hp)

Compression ratio	9.8:1

So what has changed other than the bent con rod since your 'Smoking 1.6 engine' thread (where Thefeliciahacker taught me a lesson about VW engine tolerances) are you testing same way, using same oil, did you follow Thefeliciahacker's advice of not changing the piston rings (liners?, pistons?) to new ones or were these already replaced on the engine before you got it. - https://www.briskoda.net/forums/topic/536289-smoking-16-engine/#findComment-5980790

7 hours ago, nta16 said:

So what has changed other than the bent con rod since your 'Smoking 1.6 engine' thread (where Thefeliciahacker taught me a lesson about VW engine tolerances) are you testing same way, using same oil, did you follow Thefeliciahacker's advice of not changing the piston rings (liners?, pistons?) to new ones or were these already replaced on the engine before you got it. - https://www.briskoda.net/forums/topic/536289-smoking-16-engine/#findComment-5980790

I’m testing the same way using the same test equipment. I’ve borrowed 2 compression testers from guys at work so I can test and compare them to mine.

As compression was good, other than the sonic clean of the pistons I did nothing else and all the rings are the original ones that came with the engine. when the engine was apart the only thing change was the head gasket. Oil wise I can’t say what was in there but I’ve replaced it with the correct grade for the UK.

I’ve also got my hands on 2 leak down testers so along with the compression test I’ll also conduct a leak down testers this weekend.

In the thread D.FYLAKYOS linked to there a post from a dear departed friend that "compression value varies quite extensively with valve clearance" have you check the valve clearances are correct. Another method to check could be say you're set at "25 thou" to test the 24 blade goes in easily but the 26 blade doesn't.

A mate of mine that does "classic" Jag and other race engines sets the clearances fairly quickly and only does one check and leaves it at that, for the British stuff he does at least he says one turn of the engine and they'll be out as they're not precision and the parameters worked to seem a lot narrower than the VW figures I've seen here but there might be different methods of measurement. But I've always though the VW (4-pot) engines sound a bit badger's even compared to a 1950s design and 60s and 70s built engines I'm more used to.

After the valve clearances of course all the other stuff we've been through needs checking and adjusting as required.

I think a summary of what's been done to the engine, ignition and cooling/heating may be required, new parts and materials fitted and used and adjustments made, the path taken to arrive at your current place.

If the engine was running hot before you got it that might have been for a reason other than wrong cooling set up.

Do you have an engine number or casting numbers to confirm all is what you were told it was, block and head a match to each other, all ignition and timing parts correct to applicant and not counterfeit. You have already done a lot for only a small improvement in cooling so something might have been or is misrepresented to what you expect.

I thought the 1.6 valves were hydraulic and non adjustable?