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Leon Mk I coolant tank

Nautilus

Active Member
Dec 9, 2006
547
2
Bucharest, Romania
Hello everyone

I've found some diagrams of the Leon Mk I 1.8T (AUQ engine) cooling system, and I'm trying to understand the cooling circuit.

However, they are not very clear.

Out of the (at least) 2 hoses coming into the coolant overflow / expansion tank, the lower hose goes towards the bottom of the block, in the water pump area, with a branch towards the turbo central bearing.

Does the coolant in the tank drain through the hose towards the pump (and therefore block) when the engine starts and runs? That is, when the engine starts and thermostat is closed, it runs until warmup with coolant from the tank, besides coolant already in the block, pipes and hoses, in a closed loop?

(If this is the case, there is a possibility to get quicker warmup during winter.)

Thank you,

~Nautilus
 

Nautilus

Active Member
Dec 9, 2006
547
2
Bucharest, Romania
One more question:

Does the AUQ-engined Leon have the electric "after-run coolant pump", which recirculates the coolant while the fans still run after engine cutout, and if it does have one, is it the cylinder fitted vertically to the inside edge of the radiator, on the right side?

Thank you,

~Nautilus
 

LEE69

Stage 2 Revo'd
Dec 10, 2004
21,262
74
C\UK\Devon\Torquay
One more question:

Does the AUQ-engined Leon have the electric "after-run coolant pump", which recirculates the coolant while the fans still run after engine cutout, and if it does have one, is it the cylinder fitted vertically to the inside edge of the radiator, on the right side?

Thank you,

~Nautilus

The LCR does the LC not.
 

Nautilus

Active Member
Dec 9, 2006
547
2
Bucharest, Romania
Thank you.

Is there a diagram of the 1.8T cooling system around the net, other than ETKA \ vagcat, which is less accurate?

I seek to find out how the coolant overflow / expansion tank comes into the general picture and the coolant pump also.

~Nautilus
 

Nautilus

Active Member
Dec 9, 2006
547
2
Bucharest, Romania
OK.

Background

Found out some times ago that Toyota Prius automobiles are fitted with a "quick warmup system" in the shape of a thermally-insulated coolant tank, which holds about 3 liters of coolant warm for some time, to be pumped back in the cooling system upon engine start-up.

1.8Ts can't be fitted with something similar, unless very complex and costly mods are performed (auxiliary coolant pump, separate "thermos" tank, valves, piping, wiring, dashboard controls etc).

But as we can (not easily) find out, on our 1.8Ts coolant recovery/overflow tanks communicate directly with the engine block, not the radiator. Lower pipe from the tank goes to an Y-shaped connector, from which one pipe goes to the turbo central bearing and the other one goes to the lower part of the block, above the coolant pump and before the thermostat. Tank holds slightly over 1 liter of coolant when filled to the middle joint and maybe 1.5 litres when filled up to the "G12" mark (not the wisest thing in the summer).

The design is made as such because the 1.8T timing belt also runs the coolant pump. So, when changing the timing belt and coolant pump, the coolant in the pump housing and recovery tank has to be drained away and when the tank is filled again, the coolant flows directly to fill the pump housing. (Otherwise the pump would run dry and destroy itself when starting the engine).

Were the tanks thermally insulated, the warm coolant would be drawn into the cooling system while the thermostat was still closed, and the warmup would be quicker, with less engine wear, quicker heating of the cabin heater, and a slight improvement in fuel economy. It takes energy to heat the engine, energy which otherwise goes wasted when cooling down.

First tests

With stock cooling system, the time to reach regular 90°C are:

Stone cold engine, wintery conditions - 10 to 15 minutes of driving
Cold engine after a few hours since last drive - 8-10 minutes of driving

I've performed a small experiment - temporarily insulate the coolant tank with a very good pipe insulator (Eurobatex - similar to neoprene mattresses). Insulator was about 16mm thick when stretched over the plastic tank.

Results:

18:05 - engine stopped. Outside temperature: 4°C. Everything hot.
21:47 - outside temperature: -1°C. Engine block: cool. Radiator and hoses: stone cold. Insulated tank: almost hot.
00:06 - outside temperature: -1°C. Engine block: ice cold. Radiator and hoses: stone cold. Insulated tank: warm.

As we see, the insulated tank could keep the coolant warm for at least 6 hours, and even more.

The dirty work

Removed the tank from the two screws and insulated it thoroughly with same material, every inch, all pieces glued together lip to lip, except a slit cut to see the coolant level. The slit will be also covered by a movable flap. Doubled the insulator thickness on the lower half of the tank, where there is more space, and also where most coolant stays. Glued also thin foamy insulator on the inner side of the fender, just below and behind the tank, insulated full innner fender and suspension turret. Return pipe from the A/C radiator in front of the car, which ran below the tank, had also been insulated previously with a foamy pipe insulator. Carefully left out the plastic catches for the wires and a small "overflow tube" on the side of the tank. Removed the metal plate that holds dipstick and N249 valve and insulated also the hose from the bottom of the tank to coolant ingress in the lower block.

Results:

1st test: engine warmup time (cold engine after a few hours) reduced to slightly over 3 minutes - until 90°C are reached. Outside temperature 6°C. In about 2 minutes, the temp gauge had risen to the line between 50°C and 90°C (~70 degrees?). :)

2nd test: stone cold engine, car started after 5 hours of exposure to 0-3°C outside temperature, coolant in the insulated tank rather warm. In about 4 - 4:30 minutes, the temp gauge has begun to rise, regular 90°C attained in about 7 minutes.

3rd test: stone cold engine, car started from cold in a spring day after exposure to 10-13°C outside temperature. In about 4 minutes, engine had reached regular 90°C operating temperature.

4th test: room-temperature engine, car started after 3 hours in the workshop, outside temperature 7°C. Coolant had barely cooled, maybe 2 needle widths below 90°C. In a few tens of seconds, it stood mightily at 90 degrees.

5th test: stone cold engine, car started on a cold and rainy day after staying for 24 hours, outside temperature 8°C. Warmup time: 5 minutes to 70°C, 6 minutes overall to 90°C.

Coolant temp sensor is on the opposite (airbox-) side of the block so it's not influenced.

When touching the tank after a run, insulator was barely warm at the surface from the hot air in the engine bay (and it remained cool in open air). The hot part through which heat is lost is the blue plastic cap, which may be insulated itself in the future.

Disadvantages: it works for 6 hours at its best. If the car has stood for more than 5-6 hours in winter chill, warmup time is shortened insignificantly, maybe by 1 minute, compared to stock, or not shortened at all.

Picture:

dsc00146vwx.jpg


Comparison

The Prius system is obviously light-years more efficient, due to it's specific construction:

- large storage tank, up to 3 liters;
- true "thermos" (Dewar flask) construction, able to hold the heat in for more than a day, not hours;
- separate from coolant recovery/overflow tank;
- valve to control coolant flow in both directions (all coolant is drawn by the pump both ways);
- separate electric pump to feed either storage tank or engine;
- duct goes into the cylinder head, near combustion chamber, not block.

According to user-posted experiences on Toyota forums, it heats up from overnight cold in about 1.5 to 2 minutes.

cours-2-5-bottle.gif


~Nautilus
 
Last edited:

Nautilus

Active Member
Dec 9, 2006
547
2
Bucharest, Romania
In summer temperatures, the engine heats as fast as a Prius, even below 2 minutes from a stop to 90°C.

(Obviously it takes far less energy to raise the temperature of the engine block from ~30°C in the shadow or ~60°C in bright sun to 90°C, than it takes to raise it from winter cold to 90°C :) )

Studied the way the LC/LFR radiator and SMIC compartments are built as well.

1. The BoostFactory! SMIC is separated from engine bay. After the SMIC bay had been vented with cut vents in the fender liner, closed at the previously open bottom with a plastic lid, the SMIC core surrounded with a self-made gasket made from foam to assure no intake air is lost sideways, than insulated with closed-cell foam from both engine bay and hot tarmac, it cools at its best. After a run in a day with 35-36°C (95-97°F) in the shadow, the upper side of the SMIC where the throttle body hose exits it had the same temperature as my hand, or barely warmer.

2. The radiator is shrouded with a plastic box on the sides and back, in which the electric fans run. At the same time, it has 4 plastic flaps/baffles in the bumper, to guide the air towards the core.

But the bumper design of the LC/LFR is inefficient, made primarily for looks.

The lower grilles are in a deep pocket, which translates into high pressure at speed and high flow of the air into radiator, and there is a "funnel" and lower opening in the bumper below grill to guide air into SMIC. But there is also on the left side a similar lower opening which serves no purpose, because it is below the plastic flap of the radiator. Worse, the left-side opening vents into the left wheel housing, which translates into poor aerodynamics and lost cooling air.

Steps to improve radiator aerodynamics:

- Lower air intakes into the bumper are split by factory into 3 holes each, making a total of 6 holes. Closed 4 of them: all 3 on the left and innermost one on the right with styrofoam plugs chosen to be the same color shade as the grilles (plugs are barely visible when you pay attention, invisible otherwise). The other 2 holes opened into the plastic "funnel" of the SMIC, left them open;

- Took off left side lower grill. Made a styrofoam plug to fill the space between radiator flap/baffle and foglight, as well as a lower plug to fill the space below radiator baffle deep into the bumper;

- Made smaller plugs to smooth the surface behind the grill and between edge of radiator and foglight;

- Mod is invisible once the grill is back on the car;

- Sealed cracks between plastic pieces of the radiator shroud (they do not fit perfectly flush from factory);

- From this moment, all air flowing into the bumper must flow either through radiator or through SMIC, because it has no other place to go.

Tests:

Outer temperature 35 to 38°C.
Route: city stop and go traffic plus a short highway run up to 150 kph (93 mph) then stop and go traffic again.

Effects:

Coolant temperature steady at 90°C throughout.
Engine warmup time ~2 minutes to 90°C.
Fans kick in much less often than previously.
Fans stop when engine stops. Previously they ran for a few minutes after engine off.
Engine bay temps lower than before, could be felt by hand. Previously just placing the hand above engine could toast it.
SMIC temperature almost as warm as my hand or barely warmer.

Conclusion: Leon cooling system is not perfect and it can be made better in a few hours of work with cheap materials.

~Nautilus
 
Last edited:

Nautilus

Active Member
Dec 9, 2006
547
2
Bucharest, Romania
As we're still around tampering with cooling system, took also the opportunity to wrap the fuel hoses (starting at the point where they emerge from the plastic sheath) with Eurobatex foam-rubber tubes and the metal fuel lines and fuel rail with aluminized fiberglass.

There are plenty of rumors, legends and a few facts floating around the net on gaining a few horsepower by keeping the fuel cool (like this: http://forums.fourtitude.com/showthread.php?3984508-DIY-Fuel-Rail-Wrap), or by cooling it in a small radiator, but according to the laws of physics there is practically nothing to be gained in power.

However, immediately after wrapping the lines the idle got smoother.

There must be a reason for this, and the most likely is that heat in the very hot engine bay of a 1.8T "boils" or "bubbles" the fuel in the lines and rail and impedes (slightly) the normal operation of injectors.

~Nautilus
 
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