KCPerformance BV - De Dijk 6 - 5268KA Helvoirt - Netherlands info@kcperformance.eu +31 13 30 30 000
+31 13 30 30 000


At KCPerformance we not only like to help our clients implement all kinds of minor and major car modifications, we also give advice upfront.

It's not self-evident that we upgrade a car immediately; we always check its condition first and unfortunately often find a backlog in maintenance. This may result in costly (engine) damage or even worse: an accident. All this misery can be prevented by timely and adequate maintenance. This series on "overdue maintenance" is based on our wide practical experience.

Any doubts about your own car's condition? We're there to help!

Part 1: The radiator and the benefits of preventative replacement

The radiator is an important part of an engine's cooling system. Inside the radiator the coolant is cooled by a combination of airflow from the car's speed and a fan. To enlarge the cooling surface area a radiators consists of many narrow passageways for the liquid and stacked layers of metal sheets in between. Tubes connect the engine to the radiator and a pump circulates the coolant. When the engine is cold, the thermostat is closed and the radiator is bypassed. This allows the engine to reach the optimum operating temperature as quickly as possible. Once the coolant has reached the activation temperature, the thermostat will open, allowing the coolant to flow through the radiator. This prevents the temperature from rising further. Malfunctioning of this radiator and thermostat system has a direct impact on the engine's temperature.

How important is an engine's temperature?

The moving parts from the engine are lubricated by a thin layer of oil. An optimal engine temperature is of vital concern for the necessary lubrication and the life-span of the engine. The optimal temperature for the coolant is between 90°C and 105°C, for the oil the ideal temperature range lies between 95°C and 115°C. When oil is overheated, the special additives that provide optimal lubrication will burn and the oil loses its lubricating capacity. In addition, chances of charring of the oil, the so called "Black Sludge", increase. A malfunctioning cooling system and resulting overheated engine reinforces this. A relatively simple way to upgrade the cooling system is to use a thermostat with a lower (82°C) threshold. This lowers the engine's base temperature, preserving the lubricating capacity of the oil and reducing the black sludge risk.

When to replace the radiator?

A radiator ages, this results in reduced cooling capacity. Long before it is noticeable, the engine's temperature starts to rise for a prolonged period of time. The car's temperature gauge at first doesn't show this because the on board computer interprets a temperature between 90°C and 115°C as "ok". Only when the temperature rises above 115°C the temperature indicator will reach the red area. The cooling capacity depends on both the quality of the coolant and the radiator.

Replacing the coolant is recommended every 2 years and absolutely necessary every 4 years. The cooling capacity of the radiator is already decreased by 25% to 40% after 3 to 4 years. After 8 years so little cooling capacity is left that replacing is highly recommended. For high performance cars a 4 to 6 year replacement interval is advised.

What many people and mechanics often do not know is that a radiator should not only be replaced if its condition is so poor that it's leaking! Checking and replacing the radiator and thermostat (when necessary) should be part of regular maintenance.

Put it to the test!

SAAB is well known for its turbocharged engines and the engineers were well aware that a high performance engine needs to be equipped with an equally well performing cooling system. However, as with every cooling system, this SAAB system needs regular maintenance as well: timely replacing coolant, radiator and thermostat. This makes a SAAB the perfect cand idate to investigate what the influence of a backlog in maintenance might be on the engine's condition. For this test KCPerformance equipped a 9-5 2.3 Turbo with an old radiator. For the start of the test we go back to spring 2010, 45 000 kilometers ago, with a completely reconditioned engine, built for high performance, over 350BHP in this case. A turbo charged engine requires more cooling than an atmospheric engine, and such a high performance engine is even more demand ing.

Our test radiator was about 8 years old and already lasted for 210 000 kilometers in another SAAB 9-5 2.3T. In order to conduct a fair test we cleaned the radiator from the outside and flushed the inside with a special cleaner. After this the condition of the radiator resembled the condition of a heavily used but well maintained radiator. In this case "well maintained" means regular replacement (every 50 000 km at minimum) of the coolant. The car ran on Bio-Ethanol E85 for the majority of the 45 000 testing kilometers. A few times in Germany and Italy we had to choose a lower octane fuel because Bio-Ethanol E85 was unavailable.

The results

The reconditioned engine suffered high temperatures from the beginning, despite the new 88°C thermostat. In slow traffic, the temperature rose up to 116°C. Driving in the mountains of Italy with an outside temperature of 25°C, a peak temperature of 122°C was reached! Another striking finding was the more frequent occurrence of "engine knocking" when running on regular gasoline, thus increasing the risk of spontaneous combustion. Often this is caused by so called "hot-spots" on the pistons and the risk of a meltdown of one of the pistons increases considerably. Chances of this happening to a SAAB engine are slim, as these engines are oversized and the engine management system will automatically reduce the output upon knock detection, but longer term this will always result in irreversible engine damage.

The test engine's performance started to decline and engine knocking occurred more and more frequently. In addition combustion residue was building up on an intake valve, which as a result no longer closed properly (upon poor lubrication the valves no longer slide the way they should until they eventually lock and damage the cylinder head or piston). When we eventually disassembled the engine we had the following findings: highly increased wear on all bearings from the camshaft, crankshaft and connecting rods. In addition the cylinder walls and pistons showed clear signs of wear. All together this is serious engine damage, all related to the engine's operating temperature.

A normal engine consists of several components and the important parts are lubricated by means of sliding bearings. This way of lubrication makes that an optimal engine temperature is of vital concern for long-term enjoyment of your engine. The optimal temperature for the cooling liquid is around 90°C to 105°C. The optimal temperatures for normal oils between 95°C and 115°C. When oil is too hot the special additives that provide optimal lubrication will burn and thus the oil loses its optimal function.


When introducing the 9-5, why did SAAB equip the 2.0t, 2.0T, 2.3t and 2.3T engines (the so called "T7" engines) with an 88°C thermostat when the 82°C version is clearly the better choice and standard on the 900NG and 9000 models ("T5" engine)? This had to do with emission norms, but it's clear that on the long run this increases the chances on cooling problems, oil charring and eventually the breaking down of the T7 engines because of Black Sludge. A thermostat with a lower threshold will result in better cooling and preservation of the engine.

When looking at the SAAB 9-5's on sale nowadays (with engine damage) we see that the majority of the cars is about 10 years of age. When not properly maintained the cooling system has by that time completely lost its cooling capacity and Black Sludge is present to such an extent that the lack of lubrication has grinded the engine to a halt. This process is even more catalyzed be a few more modification as made by SAAB when changing from T5 to T7. The two catalytic converters, turbo and exhaust close to or even below the sump, add up to overheating the oil. In addition, the T7 engines are built less oversized compared to the T5, giving less room for error and resulting in more extensive damage when overheated.

Has your SAAB ever been checked on Black Sludge? Have thermostat and radiator ever been replaced?