High temperatures at high speed

[StevoVZ71]

I recall you did have cooling issues. This is why you replaced the thermostat. From the description you used the over the back of the engine method to do it.

You also had concerns about the integrity of the heads. Possibly because of cooling?

Thermostat was replaced years ago which fixed any issues back then and I was going to pull the heads off to clean some of the gunk built up from the old PCV issue but decided not to in the end due to the machining costs. The motor has got hot a few times in recent years but not excessively and always due to me not checking the coolant often enough and one time when I had a tiny crack in my radiator.

To test the sensor I would have to buy a thermometer and remove so it would make more sense just to replace the sensor. The reason I thought it may be the sensor was that it was reading hot when the motor itself was not so I was just wondering if a faulty sensor would cause that?

 

[_R_J_K_]

Thermostat was replaced years ago which fixed any issues back then

Don't fall into the trap of discounting it just because you replaced it some time ago. Usually the thermostat breaks outright so it's not speed related, but there might be something stopping it from opening fully ever since you did your timing chains.

Even correctly working thermo fans will probably have basically no effect at those speeds, they're more for low driving speed cooling. Above 40km/h or something the force of the air from the speed of the car flows more than the fans do.

 

[krusing]

but there might be something stopping it from opening fully ever since you did your timing chains.

Possible a 10mm Socket ?
Are, thats where its gone ! hmmm

 

[Skylarking]

Don't fall into the trap of discounting it just because you replaced it some time ago.

Very true given that all products follow a bathtub failure curve

Unfortunately where the thermostat is makes it a PITA to remove and test…

Even correctly working thermo fans will probably have basically no effect at those speeds,

Correctly working means drawing air from front to rear of radiator.

@StevoVZ71 further to what others have said, best check that the fan isn’t trying to push air the wrong way. If it fights the normal air flow when the car is moving forward, then at some speed the fan will provide zero (or reduced) airflow through the radiator.

I‘m with gopro’ing (is it even a word) the thermo fans while driving at speed

 

[lout]

you dont have the thermos running backwards
is this even possible

 

[StevoVZ71]

I really do appreciate all the advice but I still think the most valid point is being missed and that is that I was getting high readings on the gauge but the motor itself was showing no evidence of overheating. In my experience when a motor gets hot they stink and make noise (like a ticking sound) plus you can feel the heat baking off them. This isn't what I experienced and I could put my hand on top of the intake manifold easily and could also hold onto the radiator hoses for 5 seconds or so before any real discomfort. If the motor was showing these signs of overheating then I would suspect the thermostat or something mechanical but because it wasn't is why I thought it was maybe the coolant temp sensor as I have had no experience with these and have had plenty of experience with faulty thermostats, water pumps and radiators. Plus I would imagine I would experience issues during normal driving conditions like when stopped in traffic for extended periods if there was a problem with the fans or thermostat which I am not.

So I reckon I will bleed the cooling system again and if the problem persists I will swap out the sensor. If neither of those fixes the issue then I will suss out the fans some more and look at replacing the thermostat. Those who have replaced the thermostat will know you may as well swap it out for a new one rather than pulling the old one out and testing it as it is a real PITA to swap out as Skylarking mentioned.

With the fans I am not sure what is meant by the fan pushing the air the wrong way as you can't install them backwards? Plus at 90kmh plus I would also think the fans wouldn't be doing much and that general airflow would help keep the radiator cool?

 

[_R_J_K_]

I really do appreciate all the advice but I still think the most valid point is being missed and that is that I was getting high readings on the gauge but the motor itself was showing no evidence of overheating.

The dash gauge is kind of a relative indicator, it's not as accurate as you'd like it to be and it never actually indicates an actual temperature. While it increasing from normal isn't good, on that gauge 3/4 doesn't mean it's overheating and you don't actually have any grasp on what the increase in temp is. If you can get into engineering mode you might have a better idea.

For something with that specific set of circumstances though to me it feels like some kind of blockage, so I'd also look at blasting out and flushing the radiator. If you left the radiator in the car when you were replacing the chains, it's possible you may have also bent a lot of the fins on the back side of the rad which blocks air.

Cap is also a good one to replace, they're supposed to be replaced every few years, otherwise the rubber seal can expand and cause issues.

 

[Fu Manchu]

The motor overheating won’t stink as a given.
Oil temp if available would confirm any heat problems. Not sure if VZ has engine oil temp though.

Higher speed as said should cool the car fine. As an example, many years ago I had an early 80’s Subaru that had failing electrical circuits that were a bit burny. We disconnected everything bar what was essential to the motor running, so no thermo fans. Got it back from Denmark to Perth fine but if I slowed down, the temps would come up because no thermo fan. It was a good point made earlier that I had over looked when mentioning the thermo fans.

You could have air in there again if the cap is faulty.

Sure, test or replace the coolant sensor, as you said, they are cheap enough.

 

[StevoVZ71]

The dash gauge is kind of a relative indicator, it's not as accurate as you'd like it to be and it never actually indicates an actual temperature. While it increasing from normal isn't good, on that gauge 3/4 doesn't mean it's overheating and you don't actually have any grasp on what the increase in temp is. If you can get into engineering mode you might have a better idea.

For something with that specific set of circumstances though to me it feels like some kind of blockage, so I'd also look at blasting out and flushing the radiator. If you left the radiator in the car when you were replacing the chains, it's possible you may have also bent a lot of the fins on the back side of the rad which blocks air.

Cap is also a good one to replace, they're supposed to be replaced every few years, otherwise the rubber seal can expand and cause issues.

Just replaced the cap when I stripped the motor down to do the timing chains and I do replace them every couple of years as I had a faulty cap back when I first got the car 10 or so years ago. I also thought a blockage in the radiator may be the cause as well as I have pulled it out a couple of times over the last year or so. If bleeding it again doesn't correct the issue I will drain the coolant and flush the radiator again when I replace the sensor and I might also pull the radiator out and get a radiator fin repair tool to straighten any bent fins. The radiator is only 2 years old so I would rather not buy a new one and whilst there are a couple of small dings in the radiator none of them are too bad or look like they would be too restricting.

I also thought that I need to go into engineering mode and see what the coolant temp is if it happens again which should confirm if the temps are getting hot or if it's just a misreading on the gauge. I know that 3/4 on the gauge isn't exactly overheating but I reckon you should still be able to tell the difference between normal operating temperatures and it running hot by using sound, touch and smell.

 

[EYY]

Not usually. They’ll get to 120+ before giving any other symptoms. Gauge doesn’t work in real time and is computer controlled. Often they’ll have a steady state of +-15c or so either side of ideal operating temp where the needle doesn’t move at all.

Once you’ve cooked it, it’s too late.