I have a 1998 Jeep xj engine modified with ls valves, bore out 3 over, crane cam. I have upgraded to a mishimoto radiator, replace the heater core, replace water pump and thermostat and the coolant temp sensor. When I’m driving over 2000 rpms it holds at 215 but once I go under 2000rpms it starts going up to 220 then jumps to 250. The strange thing about it is the upper and lower hose doesn’t get hot also the radiator doesn’t get hot also. Would a high flow water pump fix this or is it something bigger then that?

 

Did you replace the fan clutch?

What temperature thermostat did you install?

Did you bleed the air from the system?

 

how many miles on the new build? it is common for new builds to run hot for a while as things break in.
fan clutch, temp sensor working properly?
is coolant 50/50?

its not boiling over or any signs of overheating other than the gauge at >2000rpm

 

The fact that the hoses and radiator don't get hot means you have a flow issue. The first two things on the list to check would be the thermostat, and air in the system. After that, the water pump. Cold hoses would indicate that a high flow pump would not change anything at this time.

 

Yes I replace the fan clutch and I got The thermostat one from auto zone durlast and one form o’Reillys I ran it today with no thermostat and it ran at 210 on highway and in traffic it went up to 220 so i pop it in to neutral

 

There’s only 147miles on the engine and I replace the temp sensor last night and it gave the same reading and it’s not boiling over or any other signs then the gauge. the coolant is 50/50

 

With no thermostat, are all hoses hot?

 

yes they got hotter

 

if it were one thermostat this would seem pretty cut and dry. What temp thermostat are you running? I would think 220 with no thermostat seems reasonable once everything is up to temp, does it not guys?

just checking but was it installed in the right direction?

 

Sounds like air in the system to me. Hot pockets of air will make the gauge read way hotter than the actual temp of the coolant.
Or maybe a blockage.
Rule out t stat. Not uncommon to have a brand new one not work from local parts stores.
After filling , run it with the hood open, as soon as you start it top off the radiator and put the cap on it. Then use an IR temp gauge if you have one. I point mine at the t stat housing and at 195* on the dot, i can feel the air get hotter as well as the upper hose, when the t stat opens.
Usually about 192 or 193 it starts opening but by 195 its wide open and flowing good.
If no temp gun, just feel the upper hose. The hose to the heater core is bypassing the t stat. It should be hot to the touch pretty quick. But you will know if the t stat is working within 5 mins of starting it.

 

Ok thanks guys I'll try it tomorrow and let you know.

 

I was running a 195 thermostat and yes it was installed in the right direction.

 

A good way to check a thermostat is to put in pan of water heated to a rolling boil. You should be able to see it move open.

It does sound like at least part of the problem is air in the system based on erratic temperature gauge reading. Several heat up and cool down cycles should help get the air out assuming the radiator cap is working as it should, there is coolant in the coolant reservoir and the hose to the coolant reservoir is connected and free flowing.

 

Oops 😂