4 causes of 2jz-gte engine overheating, and some coolant boiling issues


2jz-gte engine overheats – Disaster? Maybe…

The most common causes for 2jz-gte engine to overheat can be traced to these:

  1. Wrong ignition timing, which I probably wouldn’t explain more here as I don’t have (nor do I want to) experience with.
  2. Insufficient radiator airflow – check if your standard viscous fan is operating properly. If you are using aftermarket fan, make sure you use a ducted/shrouded double fan (MVP Motorsports has a few good ones). Cheap single electric fan, or dual fan that are not shrouded are mostly incapable of cooling the mighty 2JZ, especially if you have an FMIC. The standard fan flows approx. 3300 CFM (cubic feet per minute) while the flimsy Supercheap Auto fan may only flow about 1200 CFM if you’re lucky.
  3. Standard cooling fan shrouds taken off. Taking off these fan shroud can cause cooling air to be blown improperly to the sides instead of being channeled through the radiator as it should.
  4. Coolant and insufficient coolant problem. More on these below.

Supra 2JZ-GTE engine coolant problems that lead to engine overheating are most likely from the followings:

  1. Insufficient engine coolant. Make sure to keep your coolant in the overflow bottle/tank properly topped up to the appropriate level.
  2. Faulty radiator cap. This should be the next thing you look at, especially since radiator cap is very cheap (only $5 – $20). I wouldn’t recommend upgrading it to higher pressure, as sometimes the water pump, gasket, or pipe joints may not be able to cope with the increased working pressure. But if your radiator cap is old, replace it with a new one to see if it solves the problem. If the radiator cap cannot handle the pressure within the cooling system, the water would boil at a much lower temperature, leading to boiling water spitting out of your radiator overflow bottle.
  3. Coolant cavitation within the engine. Sometimes (especially to improper fill up after coolant flush) there may be air trapped within the engine, which expands at a rate higher than coolant should when the engine heats up. This pushes the coolant out and end up having them spitting over the radiator overflow bottle as if they are boiling. Some supra owners get through by carefully keeping the coolant topped up everytime it spits, and over several days the problem simply disappeared. But it is advisable to consult proper mechanics who may de-air the engine in a more efficient way before it leads to more damage (water pump running air, etc).
  4. Coolant system leak. Leaks within the coolant system (pipe leak, hose leak, water pump gasket leak) may introduce air into the system as the water cools down after engine usage. As the system cools down, the water contracts/shrinks and air gets sucked in, becoming cavitation as above.
  5. Blown Head Gasket (BHG). This is a massive one, as the repair would involve taking the turbo assembly off, undoing the cabling and plugs on top of the engine, undoing the cam cover and cams, taking the head off, and machining the head to ensure flat seating after repair. It amounts to thousands of dollars (my mechanic did mine for around $3k – $4k) as it would take them lots of machining and in excess of 20 man hours. If you do your own car, be glad because the parts are not too expensive (only $300-$500 for head gasket kit) and it would be a great chance to recondition your engine.

BHG is rare on 2JZ-GTE running stock boost, unless something is wrong or your engine is old. But it does happen from time to time.

When the head gasket is blown, during the ignition sequence some of the hot burning air can get pushed into the cooling system through the leak on the head gasket, leading to cavitation as well as a lot of heating into the coolant.

Symptoms of Supra 2JZ-GTE blown head gasket include (but each may or may not appear, independently of the others):

  • white/milky residue in the oil, can be checked via the oil dipstick. This indicates water being pushed into the oil chambers/passages.
  • oily residue in the coolant, can be checked via the radiator cap. This indicates oil being pushed into the coolant passages.
  • white powdery residue on the spark plugs. This indicates water seeping into the combustion chambers.
  • Some equipped mechanics can do a sniffer-test with certain equipment, to see if any combustion gas exists in the coolant. This is normally done on the radiator cap outlet.
  • Pressure testing the coolant system
  • Pressure testing the combustion chambers


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