The Northern Irish pair suffered a brief falling-out last month when McDowell confirmed McIlroy was set to split from the management group they currently share.
That was quickly smoothed over and the Ryder Cup team-mates followed each other into the media centre at Merion to express their differing preferences for the second major championship of the year.
McDowell was level par in winning at a hard and fast Pebble Beach in 2010, while McIlroy was a record 16 under par when he triumphed at a rain-softened Congressional 12 months later.
"I don't think it's going to be a low-scoring US Open," said McDowell, who was also second last year at a hard and fast Olympic Club in San Francisco where McIlroy missed the cut.
"I hope it's not going to be a low-scoring US Open.
"Everyone is saying that it's going to be 62's and 63's on this golf course, which I kind of disagree with at the minute. I think they're underestimating it.
"I think there's 10 or 11 holes on this course that are as tough as any US Open I've seen. The last five holes, I can't think of a tougher finish at a US Open."
Torrential rain on Friday and yesterday had left parts of the course under water and McDowell added: "A firmer, faster US Open is going to suit a guy like me, who is not the longest off the tee.
"At Congressional I liked the way it was set up initially and then by the time the rains came down and Rory split the fairway 14 times out of 14, 330 down the middle and decimated the place, it was never going to really be my kind of US Open.
"I guess you've got to roll with the punches. You have to take what you get. Someone is going to pick up the trophy. You've got to get the attitude right.
"My US Open experiences have certainly been great but you can't really expect anything.
"I've won a US Open and was runner-up last year, but I know it doesn't mean anything. I'm the same as the other 149 guys here this week.
"I've got to go out and execute my game plan, trying to hang tough when it gets tough out there, which is inevitable."
While McDowell has won twice this season, McIlroy has been struggling for top form since his multi-million pound equipment change in January.
But the world number two believes his iron play is "dialled in" and is looking forward to taking advantage of any similarities between Congressional and Merion thanks to the change in conditions.
Asked if his eyes lit up at the sight of the downpours, McIlroy said: "A little bit. I did not really enjoy Olympic last year. I much prefer this sort of golf when you hit a shot and it stays where you think it's going to stay.
"It's still pretty tight and when you hit it in the rough you are not going to make birdie from there.
"I expect the scores to be lower than usual in the US Open but I don't think you will see scores like Congressional.
"It's probably going to play into my hands a bit more and my iron play is dialled in. As long as I can put it in the fairway I can take advantage of it."
McIlroy has been paired with Tiger Woods and Masters champion Adam Scott in the opening two rounds as the USGA continued their tradition of putting the world's top three in the same group.
And the 24-year-old hopes to take advantage of being in such a high-profile group despite having less expectations due to his relatively poor form in 2013.
"It's always nice to be part of a group like that," McIlroy added. "It's something I am excited about. I like it because there is a lot of buzz and atmosphere and it gets you focused from the first shot.
"The two majors I have won I was coming in without many expectations. In 2011 the US Open was just after the Masters (where he blew a four-shot lead with a closing 80) and last year I missed three cuts in a row before the US PGA.
"It's great to have my name on the US Open trophy and I would like to have it on there a few more times."