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The Subaru symptom that brings the most owners to Des Moines Auto Repair is a coolant or oil smell from under the hood — usually an external head-gasket leak on Subaru's flat-four engines, which shows up more in fall and spring as Iowa's freeze-thaw swings stress the seal. Caught early, it's a gasket job; ignored, it's an overheated engine.
A faint sweet smell — coolant, not exhaust — drifting into the cabin on a warm-up lap, or a coolant reservoir that needs topping off every few weeks with no puddle anywhere underneath, is the classic tell on Subaru's flat-four engines. The head gasket lets go along the outside edge of the cylinder head rather than internally, so it weeps instead of blowing, and it's easy to drive on for months before it turns into an emergency.
Des Moines gets both ends of the temperature swing hard, and that cycling — the block running hot, then cold-soaking overnight, over and over through a Midwest fall and spring — is exactly what stresses an aging head-gasket seal. It isn't unique to one Subaru model with this engine layout; it's a function of age and thermal cycling, and Iowa's freeze-thaw pattern puts more of that cycling on a gasket than a milder climate would.
What does an external head-gasket leak actually look like?
Any single one of those could be something else entirely. Two or more together, on a Subaru old enough to be due for its first head gasket, is enough reason for us to pull the covers and look rather than guess from symptoms alone.
- A sweet smell with the heater running, especially right at startup
- A coolant reservoir that needs topping off every few weeks with no visible puddle
- White or crusty residue where the cylinder head meets the block
- A temperature needle that runs hotter than usual in stop-and-go traffic
Does Subaru's AWD system mean this has to go to the dealer instead?
No — a head-gasket job doesn't touch the AWD hardware, and any shop set up to work on Subaru's flat-four layout can handle it, this one included. Where a dealer's specialized alignment and driveline tools actually matter is a different complaint: a clunk from the driveline in tight turns, or a CVT that's hunting for the right ratio, both of which sometimes do call for Subaru-specific service equipment.
If your visit is the coolant-smell problem, that's a head-gasket job we handle start to finish. If it's a driveline or CVT complaint instead, we'll tell you honestly whether it's one we should send to a dealer with the right diagnostic setup, rather than guess our way through it.
Do all older Subarus eventually get a head-gasket leak?
Not all, but it's common enough on the flat-four engine layout that we treat the smell-and-slow-coolant-loss combination as the first thing to rule out, not the last. Newer Subaru engines are considerably less prone to it than the ones from a decade or more ago.
Can I just keep adding coolant instead of fixing it?
For a while, yes, as long as you're topping it off before the level runs low — but an ignored external leak eventually finds its way onto a belt, a sensor, or the exhaust manifold, and an overheated flat-four is a far bigger repair than the gasket ever was.
Does Des Moines winter driving make the leak worse faster?
The cold side of the cycle doesn't hurt it directly, but the repeated heat-up and cool-down through a Des Moines fall and winter is exactly the stress that turns a small weep into a bigger one. We diagnose more of these in early winter than in mid-summer.