With the title I seek to side step the US vs. UK under hood vs. under bonnet monikers for the temperature in the engine compartment.
Why a specific thread about that?
Because it is a quite specific situation with the MR2.
Contrary to what one would expect, the MR2 Spyder does nót have a hotter engine room than front engined cars.
Two anecdotal examples:
When driving for all morning the sides of the central florr tunnel of my front engined diesel 4x4 gets hot, and I mean really hhhhhót. The bare metal under the carpet and insulation below the gear lever is too hot to keep my hand on.
The same route with my MR and the sanme place is lukewarm only, hardly more than air temperature.
Mind; that is a modern diesel with high thermal efficiency.
But ok, that is somewhat understandeble because of where the engine is. It is a critical clue though and more about that later.
Second one is the firewall. I meaa that is right next to the engine; between engine room and people room.
Said diesel has the exact same alumium heat reflecting isolation layer as the MR.
The diesel has 2 cm. thick heavy rubber foam and a heavy duty carpet. The MR2 ... not; just some bitumen based patches. They must be anti droning because they would melt if they would get hot so heat insulation, nah.
Yet a bag shoved forward into the footwell of the diesel gets hot and luggage in the rear cubby ... not.
´Hmmmm..´ I hear you think. That is what Í thought ;D
Back to that tunnel being understandebly hotter/cooler.
On the front engined car, the air through the front grill first gets heated up by the radiator. Then gets heated up further by the engine and exhaust (turbo).
Because of noise regulations the engine compartment is closed underneath, ensuring that only heated air flows backwards through the tunnel.
On the MR the air through the radiator has done it´s job. Does not get heated up any further. Because that is all it does, the quantity of flow is less.
Also; no engine up front so no closed bottom, meaning that the way larger quantity of ambient temp. air flowing under the bumper, mixes with the flow through the ratiator. Hence the tunnel is hardly over ambient air temp.
Now we get to the engine rooms.
I would like to give the floor to Dev ;)
Well its a very simple concept to understand but somehow people think the MR2 runs hot which it doesn't.
Actually it runs cooler than most other cars that share the same engine for the reasons that Petrus mentioned and that is there is no radiator in the engine bay adding to under hood temps.
Keeping engine components like sensors, wiring and plastics from deteriorating from heat is always a good idea but adding a fan to cool the engine bay is a bad idea because it will do next to nothing but add unnecessary weight and electrical load.
The exhaust manifold gets to be very hot and that is what people are feeling which is normal. On other cars the exhaust manifold is up against the fire wall where you cant feel the radiated heat. Generally speaking the heat does not effect the forward parts of the engine and if you apply shielding to the exhaust manifold you can reduce under hood temps but adding a fan is just a dumb idea as you are redistributing hot air everywhere.
Quote from: Dev on July 9, 2019, 23:09The exhaust manifold gets to be very hot and that is what people are feeling which is normal. On other cars the exhaust manifold is up against the fire wall where you cant feel the radiated heat. Generally speaking the heat does not effect the forward parts of the engine and if you apply shielding to the exhaust manifold you can reduce under hood temps but adding a fan is just a dumb idea as you are not redistributing hot air everywhere.
Finger on the sore spot Dev!
The exhaust temp thing is part two of the crucial running ccoler.
The first is that the outside air entering through the vents has not been heated up by the radiator. As such the engine sits in a flow of ambient temp. air instead of hot air.
See here why the firewall does not get nearly hot; there is a flow of ambient air between the firewall and the engine block.
Secondly that exhaust location. In the front engine lay out, the engine is heated up by the exhaust. On the MR the exhaust sits towards the exit of whole car! downstream of the air flowing around the engine block and as such the engine gets very little if any heat from the exhaust.
The flow of air inside the engine bay is not entírely clear to me.
Behind the car is a low pressure area which helps the exit of air.
Same thing the nappy turning upwrads at the rear, creating low pressure thus ´extracting´ air heated up by the cat.
The black shield between end damper and bumper skirt is imo límiting the air flow out of the engine bay. Probably to avoid the engiine running too cool in cool weather.
The function of the louvres in the lid is probably mostly aesthetic. The drip tray allows for hardly any flow.
Removing it will affect air flow under the lid. From moderate speeds probably more air will flow in. At low/no speed hot air will rise out.
See here why I decided to take the tray out and leave the rear shield in.
About the nappy I am on the fence.
The primairy function is to reduce sound emission but the desígn creates air extraction.
Removing it opens up the whole bottom under the engine which probaly cools the cat more but might very well reduce the air flow into the side entry, thus around the engine, thus make it run léss cool. Unless I learn more, it stays put.
For those not yet convinced of the large effects of small changes to air flow I point to the palms sized Mongos placed parallel!!! to the car´s direction.
Secondly to the 3 cm. high rubber lip I fitted behind the engine lid which noticebly reduces turbulence over the top of the windscreen.
Taking on board the negative pressure behind the car, may go some way to explaining why the tte fan blows air in to the engine room rather than sucking out as I thought it might.
Quote from: Ardent on July 10, 2019, 13:23Taking on board the negative pressure behind the car, may go some way to explaining why the tte fan blows air in to the engine room rather than sucking out as I thought it might.
Also there is a higher pressure area above the rear deck from low speed up.
A TTE ducktail or any lip like I fitted, reduces turbulence and thus improves air flow exiting at the back.
The ´natural´ flow is from the side to the rear with sóme sucked from the rear at the bottom.
With the drip tray removed, an additional entry from the top is opened up. The TTE fan blowing in this direction is confirmation.
On a side note it is rather illustrating that there is no higher pressure cooling system cap for the MR2 mk.3.
Thát would be a functional improvement of the max. cooling capacity of the car:
Reduce the % of coolant vs water, add ´water wetter´ and raise boiling temp by a higher ressure cap. Apparently there is no market for it.
I don't think messing with the coolant system is necessary. We want to keep the engine in peak operational range where it's most efficient to keep the ecu happy.
The OEM cooling system is robust and not an issue. If you try to cool it down you will run into other issues and possibly lose power.
If the car is street driven an oil cooler is not necessary either. It adds another point of failure and having the oil too cool will ruin the engine.
So basically what we are saying is don't worry about it as long as temp is ok on the dash? And be careful touching the bonnet :)
Engine bay temps shouldn't really matter if you cool the intake air down before it goes into the engine, currently running my open cone filter behind the battery and the temp drops to around 5c above ambient when moving.
Wouldn't worry too much about the engine temp, the engine itself has a HUGE amount of coolant compared to front engined cars owing to the pipework under the car etc.
There are some engines such as the Mazda alternative that does have an issue with coolant routing where some of the cylinders do get less coolant than others and can be fixed by tweaking the routing of the hoses. I don't think this is an issue with the our cars though.
Quote from: Dev on July 10, 2019, 14:29Don't think messing with the coolant system is necessary.
Yep.
The things I mentioned do not affect the operating temp. Just shift the limit of the capacity a bit but there is no need.
Hence no market even though quite a few are pushed hard.
It underlines that the mid engine does NOT run hotter.
QuoteWe want to keep the engine in peak operational range where it's most efficient to keep the ecu happy.
The OEM cooling system is robust and not an issue. If you try to cool it down you will run into other issues and possibly lose power.
Fitting a thermostat with lower opening temp. is a big NONO as that doés affect the operating condition, same as the oil cooler.
Again that not running hotter at all; it is easy to make it run too cóól!
Quote from: james_ly on July 10, 2019, 15:02So basically what we are saying is don't worry about it as long as temp is ok on the dash?
So much a non worry that if the car is in good fettle you need not lok at the dash too much.
QuoteAnd be careful touching the bonnet :)
Why?
There is no need to be careful about that; the engine room tenp is lówer than with a front engine.
Just don´t touch the black heat shield above end damper like Toyota warns you not to do.
Unfortunately many car enthusiasts suffer from munchausen by proxy for their car.
They have the need to do stuff which they think will benefit it in some way by applying fixes meant for another car on to one that doesn't need them.
This is what I tell people that want to upgrade the cooling on this car. Get a gauge first and prove it.
I have an oil temp gauge and I learned a lot from it. One of the things I learned for street driving that no matter how much I push my 2zz I cant justify an oil cooler for the street.
If anyone runs their car hard like I do then use a slightly thicker oil like a 0W-40. It will not cause any harm and will give you a little more protection if you bring the oil temps up. The downside is you will not be as efficient but its negligible.
Current Synthetic oil is now overkill and is built around some of the newer engines that run very hot by design where our engines generally run cool.
Quote from: Petrus on July 10, 2019, 16:54Fitting a thermostat with lower opening temp. is a big NONO as that doés affect the operating condition, same as the oil cooler.
Again that not running hotter at all; it is easy to make it run too cóól!
The TRD lower thermostat has its use probably in other cars that share the same engine. What it will do is give you a little more headroom if you were to race but eventually once the OEM thermostat is open it won't matter, however if you use the car as daily driver it will and can make the car run rich for longer causing cylinder bore wash. Over time you will be depleting the lubricating oils and causing more wear.
All of this stuff seems like a good idea on paper but they all have consequences. My philosophy is to prove it first than address the issue with a better part. If its not broken leave it alone and trust in the Toyota engineers.
Quote from: Dev on July 10, 2019, 18:48Quote from: Petrus on July 10, 2019, 16:54Fitting a thermostat with lower opening temp. is a big NONO as that doés affect the operating condition, same as the oil cooler.
Again that not running hotter at all; it is easy to make it run too cóól!
The TRD lower thermostat has its use probably in other cars that share the same engine. What it will do is give you a little more headroom if you were to race but eventually once the OEM thermostat is open it won't matter, however if you use the car as daily driver it will and can make the car run rich for longer causing cylinder bore wash. Over time you will be depleting the lubricating oils and causing more wear.
Well put; a lower temp stat does not change the cooling capacity one bit and on the street causes the car to run too cool.
QuoteAll of this stuff seems like a good idea on paper but they all have consequences. My philosophy is to prove it first than address the issue with a better part. If its not broken leave it alone and trust in the Toyota engineers.
Well, I cannot even see the benefit of the above on paper ;-)
Trust in the engineers I agree with although two caveats need be made:
- within the parameters the engineers were given
- the parameters also incorporate hard criteria set by laws and regulations which can (and often do) compromise the best technical solutions
This noted, there is no way that the OEM comprimise with all can be improved upon. The manufacturer spends tens of millions in the optimising by highly talented engineers. There is no gain to be made which does not have a larger price paid somewhere else.
Taking that back to the subject is per example the engine noise escaping from the engine room or made by the exhaust system, not to mention emissions.
Take removing pre-cats or any free flow improvemmnt to the main cat. That will make thermal life for components in the engine room easier without changing the operating temp. of the engine. It is however at best fringe legal in some countries and illegal in others.
Having mentioned the pre-cats, thise are a perfect example of legal requirements in the design brief for the engineers.
Toyota told them to make the design fit for all markets and one of the markets, California, dictated the pre-cats. Those are superfluous for meeting emission levels elsewhere and are in effect unneccessary heat sinks, but in just about all markets it is illegal to mod the emission stuff.
Aaaaaaarrrrghhh.
I should rephrase and reframe my writing. What I mean is if said car doesn't have a known issue leave it alone and trust the engineers. The engineers can make design flaws that needs to be addressed by the end user and that is where the aftermarket comes in or the original equipment manufacture will revise a better part that is backwards compatible like the lift bolts on the 2ZZ.
Often times people want to play engineer without understanding the repercussions of their actions as there is a depth of understanding and nuance that often times becomes a contradiction of sorts that is not cut and dry.
A perfect example is someone that has a blown head gasket which is rare on our engine design but now wants a manufacture to make a stronger head gasket when the actual issue is a defect in the mating surfaces that was caused by an overheat condition due to a bubble in the coolant system. Adding a stronger head gasket is not going to fix this issue or will it be in anyway be preventitive when you build your engine yet we also have an option for stronger head bolts when the OEM ones don't have any issues.
Some that bought the aftermarket head bolts had them come loose because they need to be re-torqued after a few hundred miles where as the weaker but adequate ones works just fine.
Temperature test 8)
It is 28 degrees here already. The sun heating up the tarmac well over that.
Took Belle out for a hot ride. Warm her up, heat her up and then rev to the max over the test track.
Did a sighting ´lap´ through most of the corners to see where the sand/gravel lies etc.
Then a hotter play sliding about a bit and finally really, RÉALLY push. Ofcourse, the ón corner I did not check, had a patch of gravel half way... The way you need to drive the MR when going fast, you are committed when going into the corner so :o and a testimony to the current set up (and the width of the tarmac) that it was a doddle to keep the car going, if not exactly pointng, where I aimed it. Also, you need to kéép it on the throttle. DO NOT LIFT!! With the forward momentum, there is not enough power to swing it round, but lifting WILL see it swap ends faster than you can correct.
Anyway, I weallywéally got heat into the engine room because all of it is relatively low speed. Mostly second gear, some third gear drifting and the ´starghts´ and only connecting coming out of a corner and going into the next.
The tyres were almost too hot to touch.
The cat was proper hot; heating up the superbike damper sleeve to melting point hence causing funny smells. Yet the deck was not hot, not warm even, just barely above ambient temp.
p.s. it is REALLY good to not have the blind spot caused by the mirror. Not just safer but confidence inspiring too.
I am going to conduct an objective experimnet on Sunday. There will be about ten cars to test, all of which will have driven far enough to be fully up to temperature,
I shall read the temp of the tops of the bumpers, (which I've noticed can vary quite a lot form the different cars I've had in the workshop).
We'll see who's hot and who's not and what kit they are running.
Quote from: Carolyn on July 12, 2019, 10:59I am going to conduct an objective experimnet on Sunday. There will be about ten cars to test, all of which will have driven far enough to be fully up to temperature,
I shall read the temp of the tops of the bumpers, (which I've noticed can vary quite a lot form the different cars I've had in the workshop).
We'll see who's hot and who's not and what kit they are running.
That would be a great research between MR2s.
To compare with front engine cars maybe the bumper is not the most representative because you will be measuring post cat/damper and that has little to do with engine location.
Next to the MAF, between MAF and engine brace would be more representative when comparing with a front engine car at the comparative location, don´t you think?!
Well, that's not an experiment I can easily conduct. For instance: which front wheel drive car and how many?
I'll just do the one I can.
I do know some two's are a lot hotter than others.
Quote from: Carolyn on July 12, 2019, 13:42Well, that's not an experiment I can easily conduct. For instance: which front wheel drive car and how many?
I'll just do the one I can.
I do know some two's are a lot hotter than others.
Front éngine; anywhichone, anywhichwheeldrive is irrelevant too as it is about the conceptual different of engine location.
Inter MR2 is interesting too ofcourse! and especially comparing different set ups!!, but not adressing the (mis)conception about the mid engine room temp.
As far as the rear of the engine goes including the rear bumper and deck its going to be hotter than a normal car, very hot.
This is why people think the MR-S is hot especially those that had previous MR2 models where it is not apparent.
Does this means the engine runs hot, absolutely not.
Our design has a nice advantage and that is with the right intake you can get near ambient temps and also have it very short.
The idiocy of the aftermarket intake makers did something stupid. They decided to make a long hot air intake by routing it furthest rear by the hot exhaust components. It was also known to suck in water and hydrolock the engine if there was a bad enough storm.
Sometimes I just cant believe how this could have been overlooked.