I had heard this could happen to the Northstar engines, but had never seen it until now. Earlier this spring, over the weekend on which the Honda Classic was held here in Palm Beach County, FL, the golf match wasn't the only victim of the rain. I did not see the "puddle" into which this 1993 Allante was driven, only the end result. There was no water intrusion into the passenger compartment of the car. The carpeting inside was absolutely dry. So it really could not be classified as a flood car. But the damage was substantial.

 

An engine gets hydrolocked by taking in water rather than air through the air inlet. With an internal combustion engine, the four strokes are: intake-compression-power-exhaust. Air compresses. Water and other liquids do not. With significant liquid inside the cylinders during the compression stroke, there's an old saying that applies. When an unstoppable force meets an immovable object, something's got to give. And it did.

 

So, why did this happen? The air inlet for the Northstar Allantes is just inside of the left front headlight, behind the grille (A). The air inlet for the 1987 and 1988 models is the highest of all model years, up on the top of the radiator support (B). It is about 29" off the ground (C). The air inlet for 1989 through 1992 models is behind and obscured by the LF headlight, through a cut-out in the radiator support (D). The bottom of this air inlet on the 1989-1992 models is at about 23" (D), about an inch lower than the air inlet on the 1993 models.The routing of the 1993 air inlet ductwork behind the bumper and under the driver side headlight then eventually through the hole in the core support is unlike anything on the earlier Allantes .

 

This routing undoubtedly played a role in the demise of the engine. The 1993 inlet ductwork (E) assembled in front of the car show how the '93 air inlet is routed. The 1989 through 1992 air duct inlet (D) is at about the same 12 height as the '93 inlet, but it goes straight in to the air box. Nothing drops down as it does on the 1993. At its lowest point, the 1993 air inlet duct is only about 8" to 9" off the ground.

 

I was not able to find a waterline on the car anywhere, to show how deep it went into standing water. Apparently it was not in water very long. But I did get a clue after we had it back together and running with a replacement engine. While test driving it, I found thatthe car had no directional signals, right or left side. When diagnosing that problem, I found that both front bulbs had burst, undoubtedly from being submerged while illuminated. So that would have indicated a minimum depth of water at least 16'~ The air inlet is up at about 24': so that still leaves plenty of height above water for the inlet. But at that level, the lower portion of the 1993 air inlet would be totally submerged. And these duct pieces are not watertight. They snap together with no gaskets, and have a small rubber valve on the bottom at the lowest point, theoretically to let water out. It is easy to see how water could be taken in through the air inlet if the water was deep enough. The air filter box was wet (F), the air filter was wet (G), and the engine had "stalled”.

 

I don't know if the damage had been done at that point, or if it happened after the car was towed out of the water and attempts were made to jump start it. But the result was "catastrophic low end engine failure;' to use a GM engineering term. Two pistons were blown and also two connecting rods. Holes were punched in both sides of the block (I), and some portions of the connecting rods (H) or pistons ended up smashed up through the valley, under the intake plenum. The engine was a total loss.

 

One other mystery surfaced during this replacement of the engine. The blown engine appeared to have a rag or pieces of cloth inside the crankcase that came out with what was left of the oil and water mix in the crank case. The holes in both sides of the block were several inches in size, but we were surprised that that much material could end up through those holes in such a short time. That mystery was solved when we pulled the intake plenum off the old engine to try to salvage the plenum. We found the valley of the block had been broken, but fortunately the plenum was untouched. With the plenum off, we found the remnants of a large rodent nest in the valley under the plenum (J) , right above where the valley was smashed. Some of the nest material had washed down into the crankcase through the punched hole. We have found remnants of nests in other Northstar engines over the years, and it's a good idea to be aware of the opening to this area if anyone ever attempts to clean their engine or engine compartment. Rodents, nest materials, flammable solvents, cleaning solution or flushing water can enter this area under the intake plenum, following the same pathway where the battery cable to the starter motor is routed. Whatever goes in will just sit there. There is no way for anything to drain out other than back the way it came in. The starter is down there too.

 

There's really nothing that can be done to change the air inlet routing on 1993 models. Northstars are a very high performance engine and need a lot of air to breathe . The issue is to be aware of the vulnerability that 1993 models have to deep standing water. If you end up in that situation with a non-running car in a deep puddle, have it towed out and have the spark plugs removed before attempting to restart it. With no plugs in the engine, the danger of hydrolock damage is lessened significantly.