Oil cooler fitting question

[mike66]

Replacing my oil cooler on a Lehman 135. The oil fittings are male threaded both ends, one side screws into the cooler and the hoses attach to the other end. The hose side seems fine, the hoses screw all the way on. The oil cooler side only goes in about 3 turns. Is this normal or will it leak? Don't want to find out the hard way. They go in maybe one turn more on the old cooler vs the new one. Are these threads pretty standard or could this be a straight or tapered thread problem? I'm using the fittings that were on the old cooler.

 

[bilge53]

Where did you get the cooler?

 

[Larry M]

Our FL SP oil and transmission coolers both have 2-3/8" NPT fittings on the coolers. Ours are made by SeaKamp.

The NPT (national pipe thread taper) fitting is tapered and that is probably why you're only able to get 3 threads. Before you screw the male part in, use a good quality pipe dope such as Rector Seal #5. You want to be able to get it apart later.


Edit: https://en.wikipedia.org/wiki/National_pipe_thread

 

[bilge53]

I got my transmission and oil coolers from American Diesel. Same fittings. How old is the trans cooler? I changed mine as purely preventative. Heat exchanger will be next.

 

[mike66]

My spares were on the boat when we got it. The fittings on the transmission cooler seemed to screw in easier and farther. Larry, probably what's going on, maybe a slightly underside bore on the cooler. I already have it installed, so I guess I'll see. I did try the hose on both ends of the fitting and it went on okay so hopefully both sides tapered.

 

[kchace]

If I remember correctly, there are 2 possible types of coolers and you need the correct oil lines for them. When I purchased my new lines from American Diesel last year I had to tell them. So mine have the "adapters" on them, but even those don't seem to be in terribly far.

 

[Ski in NC]

Most coolers have tapered NPT threads, but some have other type of threads, like flare fittings or reverse flare or who knows what else. On some of these, the NPT fitting will engage partially. No bueno.

OP- Post a photo of the threaded hole in the cooler.

 

[mike66]

Sorry, can't post pictures because I already re- mounted the cooler. Guess I'll find out the hard way if the fittings leak. Thanks for all your help.