Figuring out what I actually have

I need some help trying to figure out what I have and what I don't. I bought a 90 XJ limited a while back and am begining to build it. I remember the guy I bought it from talking like there was some great engine build up done, however I don't know how to verify what head is on the block or what block I have. Does anyone have any suggestions?

As a follow on q, The Jeep seems to run hot ( over 210 but not red line). It has gone into the red before, however the engine did not overheat. The previous owner mentioned he had installed a 3 core rad and it looks like he hardwired an electric fan to supplement the stock cooling fan. My issue is that the heater does not seem to blow hot air. It seems to be warmed over air, however not anywhere near the 200 degree mark. Is it possible the rad is too large for the engine?

I plan on replaceing the water pump, thermostat, hoses, and flushing the cooling system. I am hoping this maintenance will buy me longevity on my engine and reduce any cooling problems I may see in the near future.

Thanks,
Jason

OK - for starters, the 1990 is the last year of RENIX. Any block will work - if you use a later block, you just have to drill and tap the boss on the driver's side oil sump rail.

If you want to check - the throttle body for RENIX is held down with three screws under the airtube flange, the later HO has four screws that are accessible without removing anything.

The RENIX head has casting number 2686 - I think it's on the manifold side, midway down the length of the head, outside the valve cover (could someone please correct me if I'm wrong?)

Running 210*F is normal (mid-range on the gage) - with a little work, you can pull that down to 195* or so with no ill effects (I've been running down there for years, and neither the rig nor the California Air Police have any trouble with it. Harmful tailpipe emissions actually decreased slightly...)

OK - for starters, the 1990 is the last year of RENIX. Any block will work - if you use a later block, you just have to drill and tap the boss on the driver's side oil sump rail.

If you want to check - the throttle body for RENIX is held down with three screws under the airtube flange, the later HO has four screws that are accessible without removing anything.

The RENIX head has casting number 2686 - I think it's on the manifold side, midway down the length of the head, outside the valve cover (could someone please correct me if I'm wrong?)

Running 210*F is normal (mid-range on the gage) - with a little work, you can pull that down to 195* or so with no ill effects (I've been running down there for years, and neither the rig nor the California Air Police have any trouble with it. Harmful tailpipe emissions actually decreased slightly...)

I've gone over the break points for the cylinder heads and engine blocks sometime in the last week - if you do a quick search, you should find it fairly easily (sorry, I just don't feel like going over it all again so soon...)

The heater plenum doors are vacuum controlled, and a leaking vaccum reservoir may be causing you trouble. I know the plenum flow controls are vacuum operated - but I'm not sure about the "blend door" (mixes warm air with cold.)

5-90