MajorCommonCooling

Nissan Skyline: RB25DET Coolant Thermostat Housing Cracking

RB25DET Coolant Thermostat Housing Cracking is a common cooling fault on the Nissan Skyline on the 1993–2002 cars, and we rate it major. Putting it right costs $300 to $800 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 41 documented faults on the Nissan Skyline.

Vehicle: Nissan Skyline
Engine: RB25-DET
Years: 1993–2002
Fuel: petrol
System: Cooling

This page covers the Nissan Skyline as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Nissan Skyline faults41 documented faults on this model

What you are looking at

An annotated photograph of an automotive engine thermostat identifying the wax capsule and both disc valves. — A double-valve engine thermostat, labelled: the wax capsule is what sticks.
Dougsim · CC BY-SA 3.0 · Wikimedia Commons

What goes wrong

The RB25DET thermostat housing is cast aluminium and bolts to the front of the cylinder head. Thermal cycling causes micro-cracks to develop in the housing body, particularly around the bolt bosses and outlet port. The cracks allow coolant to weep externally, and in severe cases the housing fractures under pressure. Given that most NZ/AU R33 imports are now 25–30 years old, aged and brittle housings are extremely common. The fault is worsened by over-tightening of the housing bolts during previous service, which stresses the casting.

What you would notice

Coolant loss without visible radiator or hose leak
White residue or dried coolant around the thermostat housing
Active coolant weep from housing body or bolt areas
Overheating if crack allows significant coolant loss

How to check it

Where to look. Thermostat housing on the front face of the cylinder head, connecting to the upper radiator hose

Locate the thermostat housing on the front of the cylinder head (upper driver's side of the engine).
Inspect the housing body, bolt bosses, and the coolant outlet joining the top hose for white chalky residue or wet staining indicating seepage.
Run the engine to operating temperature and recheck — pressure makes active cracks weep visibly.

Parts involved: Thermostat.

What it costs to put right

$300 to $800 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has the thermostat housing ever been replaced?”
“Is there any unexplained coolant loss between services?”
“Has the car ever overheated?”

Now check the Nissan Skyline you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.

Nissan Skyline buyer questions

Is rb25det coolant thermostat housing cracking serious on a Nissan Skyline?

We rate it major and common on the Nissan Skyline. The RB25DET thermostat housing is cast aluminium and bolts to the front of the cylinder head. Thermal cycling causes micro-cracks to develop in the housing body, particularly around the bolt bosses and outlet port. The cracks allow coolant to weep externally, and in severe cases the housing fractures under pressure. Given that most NZ/AU R33 imports are now 25–30 years old, aged and brittle housings are extremely common. The fault is worsened by over-tightening of the housing bolts during previous service, which stresses the casting.

How much does it cost to fix on a Nissan Skyline?

$300 to $800 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Nissan Skyline years are affected?

Our research records this fault on the 1993–2002 Nissan Skyline. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.

How do I check for it before I buy?

Locate the thermostat housing on the front of the cylinder head (upper driver's side of the engine). Inspect the housing body, bolt bosses, and the coolant outlet joining the top hose for white chalky residue or wet staining indicating seepage. Run the engine to operating temperature and recheck — pressure makes active cracks weep visibly. Look here: Thermostat housing on the front face of the cylinder head, connecting to the upper radiator hose