mattsmako

My dash temp gauge is reading very low, maybe 2 lines from the left. It seems to be running fine, not using anymore fuel than usual. It will bounce to normal and then back down. I checked the coolant level, rad is normal and so is the overflow jug. It was a bit rusty in color though. I replaced the rad about a year ago as well as the thermostat and cap. If I hook up a scaner will it read the temp that the CPU sees? My understanding is that there are 2 temp sensors, one for the dash and one for the CPU. Any help would be appreciated.
01 sport 4.0 4wd\Auto

Thanks, Matthew

Fsher21

the 01 should only have one sensor in the tstat housing that runs both the cpu and gauge irrc. older models had a single wire sensor on the back of the block for the gauge only, pretty sure it was 96 and older though.

How is the wiring on the sensor on the tstat housing? How fast is the gauge bouncing?

djb383

Need to address the rusty colored coolant asap.......rusty coolant will turn a new rad into an old one really quick.

mattsmako

yeah gonna do the coolant this weekend, as for the wire to the sensor, its a single wire. the needle is moving slowly, maybe 3 to 4 seconds for it to go from cold to hot. I'm thinking a bad sensor myself but wanted to see if anyone else might have had this happen. I think I will do a thermostat also just for peace of mind. thanks for the ideas.

djb383

How old is the water pump? There is absolutely no better way to flush the motor than by removing BOTH the t-stat cover and water pump and sticking a garden hose in the stat hole and flushing out the pump hole. Then stick the hose in the top rad hose and flush out of the bottom rad hose. Flush the heater core as well.....pick one or the other heater hoses and stick the garden hose in it.

pwb

Shouldnt flush of the heater core be done with low pressure? Dont stick the hose in it, spray water in it. The pressure in your garden hose is to high If the heater core is full of dirt.

djb383

Good point....but I wouldn't think one would try tightly sealing a garden hose to anything under the hood and one would really have a big mess squirting on themselves if the hose faucet was turned wide open.... a little common sense rules.

Marcucco

Pretty sure the radiator and heater core are only rated for 15 psi.
Check the info on the radiator cap (If you have one.) to be sure.
Your garden hose is putting out 25+ psi.

Turning the hose on low isn't going to solve the pressure issue.

Many models use manifold vacuum to open and close the valve to the heater core, Maybe even all.
You may have to have the engine running to flush the heater core,
or you'll need to unhook the heater hoses and flush it separately.

djb383

The rad cap is rated ar 15-16 psi to raise the boiling point of the coolant to 255+. '97 up XJs do not have a heater control valve. I wouldn't think garden hose flowing psi could damage anything unless it was allowed to pressurize (stopping the flow). I've flushed many motors, heater cores and radiators over many years and never had an issue. Again, use common sense.

djb383

It's not uncommon for a water pump to flow 50 gals/min......will a garden hose used in typical residential applications even flow 10 gals/min????

cruiser54

When you're all done flushing at the proper PSI, install a factory stat # 83501426.

mattsmako

Thanks for all the advise, I think I found the coolant gauge problem. Leave it to me to over look the simple things. Dirty loose connection, seems to be working fine now, we'll see.
As for the garden hose, I worked for the water department before moving to wastewater, usually about 50-60psi and around 20gpm at max flow. I follow what your saying though, will use caution. I don't think anything is stopped up, I flushed and changed everything last year about this time. Who knows, may have been the 1st time anyone has done it. I think its just what the new coolant and all broke loose since then.
Thanks again for all the help.
Matthew

DFlintstone

I just use my hand to hold the hose connected to the heater hose, just to play it safe. Plus since I like to go back and forth that makes it easy.

cruiser54

Read this post over again. Talk about double meanings.......

Disoriented Hillbilly

Where was the loose connection?