The plastic oil cooler housing in your Pentastar's valley has cracked and oil and coolant are finding each other. We replace it with the aluminum version — plus the same-vintage thermostat housing — right in your driveway.
Chrysler put the 3.6 Pentastar's oil filter and oil cooler in one plastic housing, and buried it in the valley between the cylinder banks — the hottest real estate on the engine. Hot oil and hot coolant both flow through that plastic part, expanding and contracting it through every drive cycle and every Ontario cold snap. Eventually the plastic fatigues and cracks, and the two fluids that were supposed to stay separated start mixing, or leaking out into the valley where the puddle hides until it overflows down the back of the engine.
Mixed fluids announce themselves fast: mayonnaise-coloured sludge under the oil cap, a milky dipstick, coolant level dropping with no visible leak, and temperatures creeping on the highway. Oil contaminated with coolant loses its ability to protect bearings — so while the housing itself is a known, fixable failure, driving on milkshake oil is how a cracked plastic part takes an engine with it.
The thermostat housing on these engines is plastic from the same era and fails the same way, and the labour to reach both overlaps — the intake manifold comes off either way. The smart repair is both at once, and the housing goes back in as the aluminum version, which ends the cracking problem instead of restarting the countdown with another plastic part.
If your Jeep is doing any of these, this is the likely cause:
Coolant in oil doesn't just sit there — it breaks down the oil's film strength, and bearings are the first to feel it. A cracked housing caught at the 'mayo under the cap' stage is a half-day repair. A Pentastar run for months on contaminated oil can come out the other side with bearing damage that no housing replacement undoes. If you're seeing milkshake, stop putting kilometres on it and get it fixed.
Easily. It's top-of-engine work — intake off, housing out of the valley, aluminum unit in, intake back on, fluids refreshed. About half a day in your driveway and the Jeep never leaves your property.
Labour, mostly — the housing is buried under the intake manifold, so you're paying for the digging, not the part. Shops also frequently quote the oil cooler housing and the thermostat as separate jobs, which means paying for the same disassembly twice. We bundle both into one flat quote for the complete job, given to you before any work starts.
Because the factory plastic part is the reason you're reading this page. The aluminum housing handles the valley's heat cycling without fatiguing, so you fix this once. Putting another plastic housing in just restarts the same countdown.
If you caught it early — mayo under the cap, caught within days — usually no. We flush the system with fresh oil and inspect what comes out. Long-term contamination is the risk, which is why acting on the first symptom matters more on this failure than almost any other.
Send it over for a free second opinion. I'll tell you straight what the job actually involves — and if their quote is fair, I'll tell you that too.
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