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Head Gasket Failure: Causes and Solutions
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This page is a mirror of Simon's original article published in 2002 on http://www.users.globalnet.co.uk/~scuffham/Water System Mods.htm
Head gasket failure on the K-series happens for a number of reasons:
- Bad liner height tolerance.
- Incorrect bolt down torque.
- Excessive revs.
- Poor temperature control.
- Fuelling too lean (pre-ignition).
Normally it’s a combination of these.
The Problem with the K-series cooling system
The cooling problem has two sides, water temp and oil temp. What you have to remember here is that the K was designed as a 1.4 for use in low to mid-powered FWD cars. The Elise and MGF fly in the face of this in that they are both 1.8 versions with the engine in the rear (OK middle to be pedantic!).
When installed in the typical FWD car (say Rover 200), the radiator is only some 6 inches away from the engine, the sump is sticking out into the airflow under the car, and it’s only producing some 90-120Bhp.
Low-emissions
From the cooling systems design, the priority was to get the engine up to
temp as fast as possible (for emissions/economy etc) thus a closed loop
system was created with the stat controlled by the by-pass water. This means
that until the stat opens, only the volume of water in the engine jacket and
bypass pipe (also the internal heater on most cars), about 3 litres, is
circulating: not much water to heat up.
When the stat opens, it does not have to open very far to get enough cold water to balance the system, and even when the car is stationary, the whole system just starts to flow more water.
Mid-engine = bigger radiator coolant circuit
The problem comes when the radiator circuit holds vastly more water than the
engine (something like 12 litres on the Elise). All works fine for the std
car that just trolls around, spending very little time on full throttle at
speeds over 70Mph.
The problems start when the engine is up-rated, driven at 100+ mph, full throttle for 20+ seconds. What happens is that the water back from the radiator gets very cold because of the huge amounts of air forced though it at speed and the relatively slow water flow rate (as the stat is relatively closed).
Temperature Oscillations
As the engine starts to heat up (being on full throttle) the hot water
from the by-pass (this is injected into the stat housing directly onto the
stat wax bulb) opens the stat as far as it can to let more water flow round
the radiator. The water it lets into the stat housing (and on then into the
pump & engine) is way colder than the bypass water (that’s at engine temp),
this hits the wax bulb of the stat and cools it down dramatically, shutting
the stat (this takes about 2 sec’s), the engine, in the mean time, gets a
sudden injection of cold water, (at 200Liters/min pump rate), replacing the
entire water content of the engine. So all of a sudden, the cylinder head
water jacket goes from 95+C to 40C, then, as the stat is now shut, starts to
heat up all over again.
The Influence of Oil Cooling
Now, this is all made worse by the fact that the bottom 2/3rds of the
cylinder liners and the rest of the block are cooled by oil. When the engine
is in a nice FWD shopping trolley, the oil is cooled by the airflow over the
sump, in the Elise there is NO airflow (it’s covered by the under-tray).
Even with a std un-modified Elise, you can cook the oil on a track in less
than 10 minutes, (I have seen oil temps over 160c on std cars!)
Put this all together what you have is the block getting hotter and hotter (and expanding), the head alternating cold/hot (expanding then shrinking) and the head gasket acting like the slip joint between them, thus hey presto – blown gasket!
The following just details the modifications required to solve the water temp problem, you will still need to do something about cooling the oil, (I have a solution for this too!).
The solution to this sort of depends on what you use your car for.
- If you just have a road car with an up-rated engine (less than 200Bhp) that occasionally does track-days but mostly is driven around on the road, then the solution is to replace the stat with one that will not increase the volume of by-pass water to ensure speedy warm up times.
- If you have a track/race car with over 200Bhp, you need to replace the stat so that ALL the water in the system becomes the by-pass, except the radiator. The reason for this is that a stat can only open relatively slowly, so if the water temp rises faster than this, you will end up with an oscillating water temp again.
To implement the first, you need a remote stat with by-pass (ala BMW/Rover SD1 2600/etc.).
The steps are:
- Remove the old stat from it’s plastic housing, punch/cut out the centre, then put the surround back in.
- Where the hot water pipe leaves the engine bay and enters the right hand sill on the Elise (it runs under the car on the MGF/TF -Ed), cut out the T piece of the rubber pipe (this is the feed to the internal heater box).
- Fit the stat so that the inlet is connected to the engine side, the outlet to the radiator side and the by-pass is connected to the heater feed.
- Take the old by-pass hose of the engine outlet (this is the one with the two temp sender units on the branch.
- Block the outlet so that there is only a 2 mm hole in it – be careful not to damage the temp senders!
- Put the pipe back on.
- Fill up the water and test for leaks.
The reason for leaving a 2mm hole in the old by-pass is just to ensure that the sender units get a good look at the water exiting the head, I have found that with mine this is unnecessary, but I don’t use the std wiring anyway.
To do the second, you will need the same type of stat as before, plus a 3 foot length of heater hose and a T adapter to go from radiator pipe to heater hose.
The steps are:
- Remove the old stat from it’s plastic housing, punch/cut out the centre, then put the surround back in.
- Cut the radiator feed hose about 5 inches from the radiator and remove the length of the stat from it.
- Insert the stat so that the inlet is away from the radiator and the outlet is towards the radiator.
- Connect the by-pass tap to the heater hose, then run this hose under the crash structure to the other side of the radiator.
- Cut the T into the radiator return hose (C on the drawing) with the heater hose you have just run under the crash structure. (this is now the by-pass cct)
- Take the old by-pass hose of the engine outlet (this is the one with the two temp sender units on the branch.
- Block the outlet so that there is only a 2 mm hole in it – be careful not to damage the temp senders!
- Put the pipe back on.
- Fill up the water and test for leaks.
The only problems with doing this mod is that the engine will now take considerably longer to warm up and the sills on the Elise will be warm all the time.