I am US citizen. We are allowed to stay in Malaysia for 90 days.
Given that you apparently wish to stay in Malaysia for 180+ days I have serious doubts that you are a genuine tourist / business traveler and any immigration official is able to make similar conclusions. They will then go on to ask whether you are living in Malaysia illegally and whether you are working there off-the-books.
I have found two recent articles from 2013 and 2015 that describe that Malaysia (like Thailand) is now clamping down on visa runs. The rule of thumb apparently is that you are in trouble if "the passport shows more than three exit and returns within a short period of time." as stated in both articles but even your first visa run could give you trouble.
The more recent article talks of a Swiss couple being detained for two days in a not-to-land room (read: prison cell) and then released with only a one-week visa following public pressure after their case got to the press.
The older article links the practice of visa-runs explicitly to drug trafficking and prostitution which may give you an idea why it is not kindly looked upon by officials.
A comment of 2014 there also supports that immigration is sensitive to the issue:
My husband and I who are retired just made our very first visa run after having the last three months in Penag. We flew to singapore for four days. Upon arriving back in Penag we were hassled by immigration and reluctantly given another 90 days but told we had to apply for the MM2H visa. We told them we were seeing if we like Malaysia before we made such a big commitment as it involved moving 50,000 into a malaysian bank account. Immigration didn’t care.
@pnuts has posted this link to a LP forum in comments where plenty of people suggest a visa run to Singapore. However the thread is four years old and cites personal experience dating from 1999! Do also note that the OP there in fact intends to do a visa extension in KL which is also my recommendation for you!
It is definitely risky. I know a few people who did that successfully a couple of years ago and I know a person who was detained in a cell for a night and then got deported.
Usually it's pretty obvious to the immigration that you are doing a visa run, and most likely they will question you about it. For it to be successful the officer has to be convinced that you are genuine tourist and you don't work or study in Malaysia.
You can only do this for one time. Most likely if you repeat, they'll either deport you or give you a short visa.
Here's some things you can do:
On the other hand, you can also register at one of the language schools and get a 6 months legit student visa and you'll have the added benefit of the learning a new language. Note that you might be required to go back to your country and come back since 2 years ago there was a law that you couldn't convert social pass to student visa. It might have been changed now. Also you need at least 80% attendance of the classes.
If it's the first time you do this then you won't have problems. However if you do it regularly and have been in Malaysia many times before then they may look a little closer. I would also take a cheap Air Asia flight and stay out of the country for at least a couple days if you want to be totally sure.
