Subject: 2012 Lexus CT200h Premium Navi
Najeto: 264140 XNUMX mil
Symptoms: Engine coolant temperature light displays. Engine overheating if prolonged 70+ mph driving or faster if under higher load.
Not losing coolant.
Water pump / thermostat — replaced with Aisin aftermarket unit; original pump impeller had high resistance to turning by hand. Thermostat still functioned but was replaced anyways as PM with a Dorman unit Problem persisted.
Cooling system bled by loosening EHR temp sensor. Problem persisted.
Checked EHR temp sensor electrical resistance and temp sensor wiring reference voltage. Resistance was within spec range when cold and ~700 ohm at > 176 F. Did not find an issue, so did not test drive. Continued to EHR thermostatic valve, actuator, and exhaust valve. Checked baseline position at cold temp (~ 68 F).
Warmed up engine and rechecked actuator rod position. No position change even though the thermostatic valve was 195 F on the outside.
Disconnected thermostatic valve from exhaust valve pulley to test each independently for smooth range of motion. Confirmed thermostatic valve actuator rod could not move and exhaust valve could move smoothly with minimal effort.
Isolated issue to stuck actuator rod on thermostatic valve. Toyota part is currently on back order. Sourcing is uncertain and I’ve safety wired the exhaust valve open to bypass the EHR heat exchanger.
Torture test drive pending.
IN VTEC Discussion starter
140 příspěvků · Připojeno 2013
Overheat condition persisted.
Upon return home, let exhaust system cool down. Confirmed safety wire was still holding valve in open position.
Next test is to replumb the coolant hoses to circumvent the exhaust heat exchanger.
IN VTEC Discussion starter
140 příspěvků · Připojeno 2013
Thanks for taking a few stabs at it.
1. Correct, it does not overheat after idling in maintenance mode. The fan eventually turns on so maybe it’s curtailing the overheat. Need to monitor variable, trendable data rather than binary.
2. I don’t believe so either because —
Combustion chemical leak test completed. No significant combustion byproduct ground in coolant. Control test using exhaust did turn solution green vs the solution exposed to coolant reservoir which remained blue, similar to unexposed solution.
And, cooling system pressure test completed using Mishimoto MMTL-CPT-28 with warmed up engine. Pressurized coolant reservoir to 20 psi and it maybe lost 1 psi at the end of 5 mins.
3. There is one other supporting symptom. The coolant level is ballooning in the reservoir and is increasing the pressure in cooling system. Coolant level returns to same Full line on reservoir after cooling down.
4. Not sure. Need to figure out how to test it.
5. Heater functions and is the only way to lower the temp if I can’t move off the road or slow down too much. Coolant overtemp light never goes solid so it shouldn’t be detrimental.
6. Not sure how this could happen since there is only one elec connector on the water pump and only connects to pump one way. Issue could be on the pump side’s electronics but that would need another test to see if the impeller direction can be reversed.
44 příspěvků · Připojeno 2021
4) I would look around the radiator to make sure there arent any leaves / other debris blocking the radiator. And squeeze the hoses to get a rough feel for their health.
5) Its interesting to me the heating system cools the motor. That could only happen if there is at least some coolant circulation going on. Adds more useful context.
6) its possible they could have reversed the pin outs at the factory. Has happened before.
7) I believe on our cars the heater works outside of the thermostat circuit. I would check to make sure the thermostat rating matches or is below factory, and just remove it and try to see if you can replicate the previous overheating.
8) did the car overheat before the aftermarket water pump was installed? Check to make sure its flow rate is similar to stock.
9) is it the original radiator? Radiators can corrode on the inside over time causing the small passages to gum up, especially if there has been water in it that wasnt distilled.
10) has anyone ever put a head gasket or radiator leak «fixer» in it? These could also gum up some of the passages.
11) there is a chance the water pump gasket or gasket maker is blocking one of the coolant passages around it. I haven’t changed one myself on these cars so I don’t know if such passages exist.
closing statement: The cooling system holds pressure, so in your case there can really only be two issues: lack of coolant flow and poor heat exchange.
suspected coolant flow issues are the thermostat, collapsed hoses, insufficient water pump.
suspected heat exchange issues are a gummed up radiator, radiator not getting enough air flow, or improper coolant to water ratio.
Disclaimer: There may very well be special coolant system considerations I don’t know about on CTs. Im diagnosing it like a standard motor.
