88 30 Cobra Temps up amp down

I replaced the thermostat and

I replaced the thermostat and impeller on my 1988 3.0 Cobra. I was running it off the hose and the temp gauge would run up to 190 then drop down to 160. Is the new thermostat bad? Is 160 the normal operating temp? Any ideas? Thanks in advance...

"Bill, the thermostat you put

"Bill, the thermostat you put in has the opening temp stamped on the unit. Let's say that it's 160. That's the temp that the t-stat opens up to allow the flow of water. The actual temp you'll see is probably a few degrees higher. For instance, my 91 3.0 runs about 170 or so when I'm full throttle. It does cool down a bit when I'm going slower.

The normal operating temp for your engine should be in the owner's/service manual.

190 sounds a bit high before the t-stat upens. I'd make sure it's not binding and double-check the t-stat spec with the engine spec. also make sure you're getting good flow from the LU impeller. I grab the hose that runs along the spark plugs (and into the side of the t-stat housing) to make sure I can feel water pressure."

"I ran into a simular problem

"I ran into a simular problem with the new 3.0 L engine I installed. I bought a new 160 degree thermostat and it would decide to go to 210 or 190 degrees at different times (whenever). The manuel test for air leaks by removing the hose along the spark plugs to the thermostat housing and install a clear hose. It states to do this only in the lake or etc (not with a water hose). Just run at idle and at different rpms to see if any air is going threw the system. Also, another test to see if the impeller is working properly, is to disconnect the hose at the thermostat housing (again in the lake or etc.) place the hose level with the inlet where it attaches (must be pointing up vertical). Start the engine and the water should stream up 4 to 6 inches (the engine must be shut down quickly). I also checked exhaust flapper valve (make sure it is not stuck closed), spark plugs for water leak (clean spotless plug may indicate warped or leaking head). My problem was the brand new thermostat, I did not believe it (cause it was new). I just removed it from the housing and the engine never overheated so it proved to be the cause."

"Thanks for the input. I thing

"Thanks for the input. I thing the impeller was not in properly. I took it off and reinstalled it. Temp went a liitle over 160 and then went down. I did take off the hose on the plug side, and the flow seemed decent."