Pearson 365 and 367

I have a 1982 Pearson with a Universal Diesel 44 HP. It is a Kubota block. I recently installed a new heat exchanger. I can run the engine at normal cruising RPM for 2-3 hours and it never overheats (runs about 160 degrees), but when I stop for an hour or so and restart the engine, the temperature will spike to 200 or so. If it sits overnight, it won't spike the next morning when I restart it. I think I am getting an airlock in the system but don't know where it is coming from. Any thoughts or ideas?

Thanks to all for the advice and information. I did discovery an internal blockage in the HX and was able to clean it out with a water hose.  It seems this has solved the problem as I ran it under-load at the dock. I'll know more once I take it out.

Thanks everyone for the advice. I have ordered a new thermostat and some new hoses. As soon as I get those on, I will try your advice.

I have a 1982 Pearson Cutter with a Universal 5444 engine and have an overheating issue.  I replaced the impeller (the old one was still good with no blades missing) and checked the HX.  I then drained and flushed the block but now can't get the block completely refilled.  I think I am getting an air block in the cooling system which is possible especially with the water heater plumbed thru the engine.  Does anyone know of a technique to refill the block without getting an air block? It could be the thermostat, but the engine heats up very fast after a short few minutes when started from cold.

I have a 1982 Pearson 367 Cutter and am looking for a part for my Wilcox Crittenden Headmate 1460 toilet.  I need an "inlet valve cover" that fits onto the manual pump assembly.  It is listed as number 8 on the Headmate brochure and is listed as part no. 019596 in the parts list.  I would like to buy a used pump assembly or just the valve cover, either way.  See the attachment.  Any help would be appreciated.

I also had this done on my 367.  When we found that the shift was out of true in 3 places, the yard determined that the strut did not allow alignment with the v drive. They removed and re bedded the strut to solve the problem.

I just removed the port spreader light on my 1982 367 cutter.  I could not find any identification markings on the bulb, but it measures about 4.25 inches across.  It looks like a typical sealed beam and the marina has it.  I think it is a GE bulb.  My problem is that the gasket is missing where it inserts on the frame.  Any ideas where I can get the gasket? 

I have a 1982 Pearson 367 and my headsail inventory includes a fairly used 130 and a fairly new 150.  I am inland on the lakes and am constantly tacking.  Eventually, we will turn south to the big water, but for now I may remove the furling staysail and sail with either the 130 or the 150.  I want to purchase a Yankee cut 90 (which is what the specs called for on this rig) as I understand from this forum that the boat sails well with the 90.
My questions are:
1) Should I sell either the 130 or 150 and apply those dollars to the new jib?
2) What is the market for used sails?

Still learning

I also am trying to tune our Pearson 367 and looking for advice on where to find this information.  I did not locate it in the manual.  Any help would be appreciated.