Elbow is a common cause, but......
Gil:Tim & Bob are correct. This is a very common cause of overheating but I would check everything else first.Start at the Raw Water Strainer. Close the thru hull and pull the strainer out, be sure that there is nothing in the strainer. Then open the thru hull and make sure that water is flowing in freely. I had some gravel in the intake once.Next go the raw water pump and check the impeller. Change it while you are there regardless if YOU think it needs it or not. If the old impeller is still in OKAY condition, you can save it as a spare. Be sure to check the belt tension before you R/R the pump. If the belt is loose you may not be getting the proper cooling either. May as well replace the alternator and water pump belts at this time. Save the old ones as spares, for an emergency. The next place you can have a problem is in the heat exchanger. This area has raw water and anti-freeze in it. You can pull the front cover off and see if ALL of the passages are clear. If you can get some long Q-tips like that have at a Dr.'s office you can swab out each tube. I have not had the front cover of the exchanger off, so I do not know if you need a gasket or not. Be sure to check the thermostat too. The next place is the mixing elbow. As Tim mentioned I posted some pictures of the procedure. It is not difficult, just takes three hands. You need to make sure you have a gasket for the exhaust manifold, because there is a good chance that yours will not be any good once it is removed. The the last place if you have not found your blockage/problem is the exhaust hose. These can come apart on the interior and also get blocked. This is a difficult one to replace too but not impossible. A couple of other things to look at are your hoses. You want to be sure that the hose from the intake to the pump are not collapsing from the suction. If you hoses are soft this can happen and it will restrict the flow. I'm sure that you are going to find your problem somewhere in the system. If you do not then you will need to pull the head and see if there are any cracks. This is doubtful but would be your last resort.