Hydrolocking/Intake Manifold issue?

[GMTruckGuy74]

My step-son took his '98 Buick Regal LS with the 3.8L Series II V6 to the local Oil Change/Car Wash place because his low coolant light kept coming on. They flushed his engine with the pressure machine, put in new coolant, and replaced his "rusty" fuel filter. He left the place and the car was shaking like it wanted to stall out - the Service Engine Soon light was flashing, he said. I told him to meet me at the local Advance Auto Parts store so they could do a free OBDII code read. He got code P0300 - random multiple misfire (they said it would need to go to a mechanic). Tried to restart the car and it wouldn't crank over. Pushed it into a parking spot and left it to see if if would restart after cooling down for a while. 2-3 hours later return and it wouldn't crank over. Called roadside assistance and had it towed to the local repair shop.

Got a call from the shop owner today. Diagnosed the problem as engine cylinders being "hydrolocked" with engine coolant. Asked if we ever had the intake manifold replaced; told him we've owned the car a year. He said the 3.8L V6 Series II engines are known for cracked IM's since they're a plastic design. Likely the pressure from the recent engine flush cracked it enough to leak coolant into the cylinders. Says that a new intake will be needed and suggested replacing the old looking spark plugs and wires (tune-up) since we don't know when it last had one (and the fact the plugs have been soaked in antifreeze). Cost... $975.

Step-son is calling grandmom to see if she can cover the bill until he makes enough to pay her back (otherwise I'll have to use the "truck fund" money to cover the repair until a couple of his paychecks come in). Would I be correct in assuming that the upper & lower intake manifold gaskets are being replaced too? I will verify with the shop owner when I call him back (after we find out if grandmom is helping), but thougth I'd ask here first about this whole issue.

[Intrepidation]

I can't believe the shop just dumped more coolant in without first checking for the cause of the leak. Coolant levels never really change unless their is a leak, and therefore a bigger problem somewhere. And what on Earth was the point of using a pressure flush if its obvious there's a leak somewhere? Its only going to exacerbate the problem. This is why I'm very selective about who works on my car when it isn't me.

Upper and lower gaskets would be replaced, since the upper has to come off to access the lower manifold. Its worth noting that the lower manifold gasket is the one that seals the coolant and keeps it from going to the cylinders, the upper is a vacuum seal. Intake manifold gaskets are a common problem with the 3800.

[GMTruckGuy74]

Thanks for the info, Dodgefan. I did confirm with the shop owner that the U&L gaskets were going to be replaced. He said the same thing as you - a real shop would have performed a pressure test on the system first before hooking up a pressure washing machine for a fluid wash. He said it likely was cracked before that (which would explain the coolant loss) but that the process didn't help the situation.

I gave the go-ahead for the work to be done and the owner said once they get the intake manifold off they'll double check to make sure that is the cause. In hindsight, he should have used this shop for the coolant flush, as they were the ones who did work on my '96 Cadillac FWB and I was happy with their work. He was in a rush to get to work and stopped by the quick lube place as it was on his way.

Good thing for grandmom's

[Intrepidation]

Personally I'd go back to that speedy lube place with the bill and a note from your shop about this, since pressure flushing the system (without even investigating the leak), made things worse.

[Guest Jarhead]

Gentlemen, 

read your alls thread and found that I did in fact hydrolock engine when I pulled of my intake manifold on my 73 NOVA hatchback.  Pulled spark plugs and gave the cylinders a shot of WD 40.  Let it air dry and then put it all back together, and set the firing order correctly.  She purrs like a kitten now, thank you all for the information listed here!!  Helped a lot.