Hello all, new Prius owner here. Found a 2014 with 30k miles and jumped on it at Carmax. Put 6k miles on it since July. This Sunday when we started it the engine shook, then everything smoothed out. Took it to the shop thinking maybe a classic head gasket issue. Carmax decided the transmission needed to be replaced. They’ve already started the work and it will be ready tomorrow. My concern is that it doesn’t look like CVT failures are usually associated with shaking engines on a cold start. But to be fair, I haven’t noticed any coolant drop. Has anyone else had a similar problem where the CVT died this early or caused engine shaking on a cold start? Any recommended questions for me to ask the mechanic when I pick the car up? I’m still not sure what led them to blaming the transmission.
Coolant loss is not immediate with hg on these cars. A required Transaxle change is a stretch, unless they have specific transaxle codes. The typical hg shake in a Prius is a fast clearing misfire that may not set codes. Generally the engine runs perfect for the rest of the day or even for weeks. The engine has a damper to allow some sync issues such as those caused by a misfire. That damper makes the rattling.
Is there a good way to test for a HG leak when it only seems to happen on cold mornings after car’s been sitting? Not sure how to prove to the mechanic they’ve done the wrong service. :/
Called mechanic again this morning and he said he did block test it and found nothing. I’m still not convinced it’s been diagnosed correctly based on the symptoms. :/
Ask them how they knew the transaxle failed? What codes and other signs? How many times has the cold start shakes happened? Is this Carmax work covered by warranty? If it happens again you know they did not fix it. Traditional head gasket tests are usually negative at first if the problem is not repeating frequently. Typical tests are combustion gas in the coolant, leakdown test and or a borescope inspection for a steam cleaned piston. I think the borescope is the most conclusive in early hg stages however it is a bit of a job. On these engines coolant in the oil usually does not happen. Eventually loss of coolant becomes obvious and rattling may start occurring often. There are other misfire causes like plugs, coils, injectors etc but they throw codes and happen while driving, not just on cold start. An egr that does not close at low rpms will run bad as well but not just on cold starts. Nevertheless many spend money "fixing" all those possible issues.
My car has 79k miles and occasionally does it in very cold mornings (less than 40 F). I just switch car off, turn it on again and it goes away. No transmission replacements at all. I had this car since 40k miles with zero engine issues.
There are two tests I perform to confirm or deny an early stage headgasket problem. First is to perform a cooling system pressure test on a hot engine, and leave the tester pump in place overnight. Next day, pull the sparkplugs and inspect the cylinders with a videoscope for any coolant. Second test is to do a leak down test (sort of). Position the crankshaft so the test cylinder is at TDC with the valves closed, then pressurize the cylinder with full shop air (150+psi) and look for pressure build in the cooling system. Posted via the PriusChat mobile app.
