2001 Volvo S40 coolant leak now won't start

Car began steaming/overheating after approx 20mins of around town driving. Coolant sprayed onto back left corner (passenger) of engine and approx 1 pint of coolant leaked onto ground near front passenger side tire. Car won’t start. Cranks but won’t turn over. Mechanic cannot find leak based on gross visual inspection or compression testing. Replaced ECT sensor after it erroneously indicated exterior temp of -40F(actual temp +30F). Car still won’t start. Thank you.

You need a better mechanic. If coolant sprayed onto the back of the engine it had to come from somewhere, and that somewhere should not be all that difficult to figure out.

How much coolant was left in the radiator after the leak?

Did the engine stall when it overheated, or did you shut it off?

Can you smell coolant in the passenger compartment?

Is there anything electrical/electronic where the leaking coolant sprayed? Did the compression test yield good numbers?

Mechanic says he needs to get the car started before he can find the leak. Nothing is obvious to the eye. Compression was good; no leak resulted.

Not sure. We added about a quart to the overflow container.

We shut off the engine due to the steam coming out the hood.

No coolant smell inside the car.

I asked the mechanic the first question thinking perhaps a distributor cap got wet. He said he didn’t think anything electrical got wet (and there is no distributor cap.)

The compression test yielded good numbers. The key issue is that the car wouldn’t start and further diagnosis of the coolant leak needed a running engine.

I fail to understand why locating a coolant leak requires a running engine.

If coolant sprayed itself into the engine compartment there is a leak, and it shouldn’t be that hard to find.

C’mon, the coolant came from somewhere.

From where did it come?

He should be able to throw a pressure tester on the radiator and locate the leak. Maybe he doesn’t have a pressure tester…

He did a compression test (I assume that;s the same as a pressure tester on the radiator?) and
nothing leaked out.

Is it possible the overflow tank itself overflowed, say due to a faulty thermostat?

In a compression test the spark plugs are removed and a pressure tester is either screwed int the spark plug hole or held against it. The engine is cranked and a pressure reading is shown on the gauge. This is done for all cylinders.

A pressure test of the cooling system is done by attaching a pump and pressure gauge in place of the radiator cap and pressurizing the cooling system and seeing if it holds operating pressure. If it doesn’t -you have a leak and the mechanic has to keep pressure in the radiator while he listens and looks for the leak.

Neither test can explain why your car won’t start unless your compression is really, really, bad. You haven’t made it easy to help you because you left out the year and mileage but there are only 4 things that will prevent a cranking engine from starting. Spark, fuel, compression or timing.

Thank you for your explanation. My car is a 2001 S40 with 90K miles, and is in general very well maintained. I will have to talk to the mechanic to verify if he did a compression or pressure test. He said compression, but … And my volvo doesn’t have a radiator cap (that surprised me a few months ago
when I went looking for it.) To fill the radiator, I put coolant in the overflow container.

Is your mechanic experienced with Volvo? This doesn’t seem like it should be a big problem and the mechanic is stumped. Get the car to a different mechanic, or perhaps a Volvo dealer. Make sure the new shop is one that specializes in Volvo.