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Warped Plenum


pretty bad
Typical Repair Cost:
Average Mileage:
107,000 miles
Total Complaints:
2 complaints

Most Common Solutions:

  1. remove and replace plenum (2 reports)
1999 Pontiac Bonneville engine problems

engine problem

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1999 Pontiac Bonneville Owner Comments

problem #2

Aug 062010

Bonneville SE 3.8L V6

  • Automatic transmission
  • 167,000 miles


The gasket under the plenum failed and coolant began leaking into the cylinders. I had two independent mechanics tell me that with the engine leaking that much coolant into the cylinders, and the resulting hydro lock (engine wouldn't even turn over) I would be better off replacing the entire engine. Both estimated a cost around $3500-$4000 for the job. Fortunately, I was talked into simply replacing the plenum and gasket myself and moving on. That only cost me $350 and a couple long days in the garage. Now, 35,000 miles later, my Bonneville has over 200,000 miles on it, but it is beginning to lose coolant and I suspect the defective plenum design has struck again.

- , Lawton, OK, USA

problem #1

Apr 142004

(reported on)

Bonneville LE

  • 47,000 miles

From what I have found this is a fairly common problem on these 3.8 cu engines. The plenum is made of plastic which warps and allows for leakage of the engine coolant. Considering the number of 3.8 cu engines produced and in use there should be some sort of compensation or class action filed against G.M.

- , Onalaska, Wi., USA

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