Hi guys,

I’m close to get another Felicia pick up, up and running but as it gets closer to being back on the roads I’m seeing issues I’ve not seen before.

Giving the car a shack down I’ve notice that the temp gauge sits at around 100degrees when driving as pictured.

When the car is parked up the temp sits at 90, rising to around the 100 degree mark and the fan kicks in and pushes the temp back down quickly as expected.

The Felicia is a bit of a mongrel in that it started life as a 1.3 but now has a 1.6 in so I’m expecting issues like this.

What do people think the reason for the temp sitting so high could be?

My rad measure roughly 60x40x4 (is this the correct size?). The thermostat housing was replaced and came with a thermostat installed.

Thanks in advance

Rob

Rob,

is the thermostat correct for engine,

thermoswitch correct for fan and engine and fully working, and wiring and connections good

gauge correct to sender, and wiring and connections good

rad you have asked about,

what about the rest of the cooling and heating system is it standard and is it all in clean and good working condition,

was the system fully bleed,

engine block cleared and clean,

coolant to correct quantity mix and type,

radiator grill free from obstructions,

engine oil level, type, temperature

checked brakes for binding

checked exhaust system for any partial obstruction and soundness

engine set up fully correctly

Usual basic checks first, check and recheck and check again and cross reference any readings and information you see and get.

Engine is running warm not hot, so far.

Others will be along with more specific and better information and advice.

Good luck.

ETA: I once had some very strange reading on a first test run on doing something to the cooling system and I had left some blue-paper in the thermostat housing (to prevent muck getting in) but failed to notice it and remove it before reassembling, the paper was thick enough to take a while to fully wick the coolant through and gave strange readings on the gauge on the test run. a silly schoolgirl error.

I am not suggesting this is the case for you but an example of thinking all has been checked when it wasn't.

Edited 1 March1 Mar by nta16
ETA;

On 27/02/2026 at 20:16, Rsedmonds said:

What do people think the reason for the temp sitting so high could be?

I had a similar problem:

https://www.briskoda.net/forums/topic/477921-skoda-felicia-weird-temperature-problem/page/3/#findComment-5375868

First of all check for leaks ,not by vision only but with a special tool in a repair-shop.

Remove check and replace the thermostat sensor, some times a small amoutn of dirt can cause false indication in the cluster gauge.

Remove any air bubbles from the system.

Remone the old coolant and replace it with G12 (not G12 plus).

The radiator size sounds like 1.9D. how does the fan look like?

Does the heater work when it overheats like this?

Does it have air guide around the radiator, under the bumper cover? Without it, the air will just flow around the radiator, which would explain why it works properly on idle.

Is the fan wired correctly? Does it push air into the engine bay (I've seen someone having similar issue and the culprit was the fan spinning the opposite way, effectively blocking the radiator)

10 minutes ago, Papez said:

(I've seen someone having similar issue and the culprit was the fan spinning the opposite way, effectively blocking the radiator)

Plus the wiring on scales to be in reverse, 2nd scale in low speed and 1st in high, inevitably the radiator fan motor burned prematurely.

https://www.briskoda.net/forums/topic/485671-bosch-radiator-fan-for-felicia-help-wanted

You can do a smoke test to see if the fan is sending the air in the correct direction (good point about fan guide/cowl being present and fitted correctly.

I was once sent a wrong eclectic fan motor (with blades) and fitted it after checking it worked but forgot to check in which direction, as it was part of a kit the manufacturer supplier took a lot of convincing they had sent the wrong fan in an otherwise correct kit and I practically had to stand on my head to read an upside down label through the recessed rad grille to give them the model number. They apologised and sent the replacement to arrive next day but the fan kit installation was little involved so I wasn't best pleased to have to do it twice. It did teach me to fully check items delivered next time (after this) and there was a next time but the fan was correct. Sod's Law always apply check and it will be correct forget to check and it will be wrong.

29 minutes ago, nta16 said:

You can do a smoke test to see if the fan is sending the air in the correct direction

If has a/c he can turn it on immediately after the engine starts,the fan will start spinning and he could check the air flow direction.

Hi, the fan is turning in the correct direction.

The measurements I took are not correct, the width of the radiator is only 285mm so when the previous owner did his engine swap he failed to fit the wider 322mm radiator from the donor vehicle. This suggests that it’s been running hot since the swap which could also explain why the head gasket was blown when I bought the car.

I’ve ordered the correct size rad and as the radiator cowl won’t fit from the smaller radiator I’ve ordered a 12” eBay cheapo radiator until I can find the correct cowling.

1 hour ago, Rsedmonds said:

285mm so when the previous owner did his engine swap he failed to fit the wider 322mm radiator from the donor vehicle

285x485 or 285x590? The former is 1.3 radiator, the latter is 1.6.

322x590 is 1.9D or 1.6 with AC.

By air guide, I meant this plastic in front of the radiator:

If the previous owner changed radiator, he could've left it out instead of modifying it for the larger radiator.

One more thing, it bad/clogged coolant pump could do that. But that would be probably noticeable on idle.

Edited 2 March2 Mar by Papez

Coolant sensors with Yellow ring always caused me problems, only those with Blue ring work as they should be (i have a/c).

27 minutes ago, D.FYLAKTOS said:

Coolant sensors with Yellow ring always caused me problems, only those with Blue ring work as they should be (i have a/c).

Bad coolant sensor would show high temperature all the time.

But since the temperature looks normal on idle, it means that the coolant sensor is fine, as is the fan switch and thermostat valve.

So wee need to find cause of high temperatures at speed. That could be caused by:

• Bad airflow (missing guide in front of the radiator, blocked inlets, partially blocked radiator, fan connected in reverse)

• Bad coolant flow (bad coolant pump, wrong plumbing, blocked radiator, bad thermostat valve)

• Gas bubbles in the coolant circuit (for example, from failing head gasket)

That's all I can think of. Striked through options have been ruled out so far.

44 minutes ago, Papez said:

Bad coolant sensor would show high temperature all the time.

Ιn my case i had issues only when the coolant was fully warm, the needle was making some kind of ''jump'' up and down and drove me crazy, the culprit was some dirt collected in the side of the base of the sensor.

After remoning and cleanit thourougly this phenomenon stopped.

14 hours ago, Papez said:

285x485 or 285x590? The former is 1.3 radiator, the latter is 1.6.

322x590 is 1.9D or 1.6 with AC.

One more thing, it bad/clogged coolant pump could do that. But that would be probably noticeable on idle.

aahhh, I didn’t realise there were 3 different sized radiators. On your figures I do have the correct radiator fitted for a 1.6. Looking at the radiator it’s not in the best of conditions so a change won’t hurt.

Regarding the coolant pump it was all changed while doing the rebuild as a matter of course rather than a necessity I also changed the water pump, thermostat housing, thermo stat and temp sensor. The coolant hoses were also connected wrongly to the thermostat housing but after asking on this site the correct configuration was found. I still need to find thermostat housing to the heater matrix hoses as the ones fitted aren’t correct and thought they have flow are tight against the air box.

The air guide is there.

@D.FYLAKTOS The sensor fitted does have a yellow ring but as previously stated if at tick over the needle sits perfectly on 90degree. Do you know the difference between blue and yellow.

@Papez

50 minutes ago, Papez said:

So wee need to find cause of high temperatures at speed. That could be caused by:

• Bad airflow (missing guide in front of the radiator, blocked inlets, partially blocked radiator, fan connected in reverse) radiator guide is present, flow was flushed on rebuild, newer larger radiator ordered

• Bad coolant flow (bad coolant pump, wrong plumbing, blocked radiator, bad thermostat valve) coolant pump changed during rebuild, plumbing previously checked but matrix to thermostat housing pipes incorrect, new radiator ordered.

• Gas bubbles in the coolant circuit (for example, from failing head gasket) head gasket changed, will check coolant pressure.

Does anyone have any idea where I can get the heater matrix coolant hoses. I did originally post asking but didn’t get any response?

4 hours ago, Rsedmonds said:

The coolant hoses were also connected wrongly

I wonder who and most of all how he manage to do this?

2 hours ago, D.FYLAKTOS said:

I wonder who and most of all how he manage to do this?

There’s 3 that all sit together on the back of a 1.6 thermostat housing and he put them on wrong. When I bought the truck he even said that the heater was crap and didn’t work. If memory serves me correctly this is how he had them arranged.

Little update.

New radiator arrived today and has now been fitted, but looking at the old one removed I couldn’t see any really issues other than it was showing its age.

I’ve taken it for a run as much as I legally can and to be honest there isn’t any significant change. The needle does sit slightly lower but I have to bear in mind the front bumper or grill was not on the car. The picture attached shows the temp when I pulled up and by the time I got the camera on my phone open the temp had already started to fall.

Does anybody know the dimensions of the heater matrix pipes as I’m thinking of splicing a piece of pipe in to release the tension on the one that stretched?

Also can the heater matrix be removed without removing the heater box?

Regards Rob

17 hours ago, Rsedmonds said:

Also can the heater matrix be removed without removing the heater box?

On LHD cars, some screws have to be loosened to lift the box a little to clear the battery holder. The battery is on the opposite side on RHD cars, but I'm not sure if there's something else that may interfere.

I’ve had the pipes off and the flow through the matrix is good. I have put a piece of copper pipe in my problem pipe to extend it and take the tension out of it. I’ve pressure tested the system this morning and it’s hold good pressure.

Later I’m going to vacuum fill the system and put a coolant system flush in it and leave that over night, then flush and fill it tomorrow.

Be sure to follow the instructions on the coolant flush if it is a cleaner, after flushing it out I find another back-flush (with water) and then flush and drain gets more crud out that just a flush drain but most don't bother to go that far stopping at the first flush drain. On old cars I also remove and clean and do the flushing and back flushing at engine block (drain plug aperture) radiator and heater matrix separately as a first clean of a system that is new to me. All so much easier with a vacuum pump rather than tap water pressure, gravity and lungs power.

On an old simple car I once connected up the two heater matrix hoses the wrong way round by mistake but it still gave lots of heat.

6 hours ago, Rsedmonds said:

put a coolant system flush in it and leave that over night, then flush and fill it tomorrow.

Ι have never read directions to ''leave it all night'' in a products of this kind.

Usually is used when the coolant is hot and then you rinse.

I put the flush in about 18hrs ago running it up to temp then left it to do its best over night. I’ve just given it its first flush of the day and I’m now sat in the car running it up to temp writing this message.

I’ll repeat this at least twice more as I flush out any remaining cleaner.

Doing this over and over again also give me the opportunity to practise with the vacuum filling system I haven’t yet had the chance to use yet but it’s going to get abused today. 😂🤣😂🤣

Edited 7 March7 Mar by Rsedmonds

The risk of leaving things to soak is possibly more time for debris be loosened and drop and/or build up at points and possibly flushing at even reasonable pressure may dislodge and just pass by some of the build ups or bits. Possibly back-flushing at reasonable pressure, after initial drain and flush of cleaning, may stir things up a bit and move more. This to be followed by forward flush(es) again until clear.

Doing the flushes and back-flush in sections, engine bloc, radiator, matrix, connecting hoses and pipework, possibly gets more out as well.

Once you have done a thorough clean and flushes and back-flush hopefully this will set you up well to just do the two-yearly thorough drain and refills of coolant/antifreeze to keep the heating/coolant system in good reasonable working order (subject to parts replaces as and when required too).

Keeping the outside of the radiator, rad grille, and fan reasonable free of debris (and not blocking rad grille with ornaments) should also help with running temperatures.

Of course the second type of engine cooling is the engine oil so regular timely changes using good quality oil will also help engine running temperatures and generally.

Wel that’s not changed a thing. 2 flushes with the thermostat out and 2 flushes with the thermostat in.

Took the car for a drive and it took longer to get there but get there it did, back to where it was and I’m not sure whether that it’s limit or it’s the fan kicks in (which it does) and brings it back down. I had a cabin temp of around 50c but I’m at a loss now as to what it can be and can’t afford the coolant 😖.

It was unlikely to have been the coolant but having a clean system and any bit cooler helps and delays getting too warm/hot which helps with running and finding issue.

Back to checking and rechecking basics as previously listed in several posts.

As you have changed from a 1.3 to a 1.6 engine the cooling needs to be adequate for the 1.6.

You have fitted a lot of new parts now were you able to check the parts were correct for engine and worked correctly before fitting and that they were fitted correctly (water pump, thermostat, etc.,) checked for bubbles again and other signs of head gasket failure again, any blockages or partial blockages at new parts areas, coolant and exterior.

I forget is engine set up correctly timing wise, correct plugs, air filter and air to engine unrestricted, exhaust unrestricted, brakes not binding.

Have you tried heating the engine up fully when parked up and getting it warmer to check when fan cuts in and out - to eliminate the cooling or heating effect of the vehicle being driven and moving along the road.

It's (hopefully) probably going to be something silly that's been, missed or not noticed. Why not do a video (landscape) of front of vehicle and inside engine bay with the engine up to temperature / warmed up / warmer hot to see if others can spot something that might be amiss.

18 hours ago, Rsedmonds said:

I’m not sure whether that it’s limit or it’s the fan kicks in (which it does) and brings it back down.

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