here's a new one.. rad pushing, not sucking..

I searched the threads and find all typical or common issues that are cooling related. Here's one that I couldn't find a thread on..

it seems that my rad is pushing the coolant into the overflow just fine, when it needs it back in the rad it's not sucking it back in... this creates a problem with the temp sensor reading all messed up and kicking the electric fan on/off every 20 - 30 secs when cold..

any ideas why it wouldn't pull the coolant back into the rad when it pushes it out just fine?

thanks
rob

98 cherokee sport 4L auto

Your cap's bad.

x2 On the Bad cap.....

crap.. I just changed it... like a month ago.

thanks

My 98 cap is 16 psi, what is yours?

The radiator cap has two valves in it - the large outer valve is the "pushing out" valve, and it's the relief for the overheat. The small silver disc in the middle is the "sucking in" valve - it should be under considerably less spring tension (just enough to keep it closed.) You can check by putting the point of your pocketknife blade (you do carry a pocketknife, don't you?) under the edge of the cap and gently prying it up - it should move fairly freely. This is usually the valve that's defective, if a cap is bad "out of the box."

Other possibility? The hose to the overflow has gotten soft, and is collapsing under suction. If the cap tests good, replace this hose.

Oh - and make sure there isn't any loose crud that could be blocking the port in the bottom of the overflow tank. This is usually neglected during maintenance, and you'd be surprised what I've found in here sometimes...

very very good reply 5-90 ..
mine is a 16PSI cap also muckleroy

going to open up my pocket knife right now and check it.. LOL :scottm:

New caps cannot be the lever kind - they don't suck. Are you using the plain two ear or coffin style?

I ran a lever cap for years fighting a overheat problem, and found it contributed to a loss of coolant getting back in. Now I can't keep the tank filled up enough . . . I sure hope it's a simple leak.

I have no clue what the difference is between the two ear or coffin style. so I can't answer that. the cap i replaced it with is a standard stant 16psi cap

i've been pretty sick the last couple of days so I haven't had the time to get out and mess with it much. i did clean out the overflow and blow out the hose from the rad to the overflow. looked ok.

i'm back to driving it today so we'll see if anything has changed

crashxxx said:

and kicking the electric fan on/off every 20 - 30 secs when cold..

98 cherokee sport 4L auto

Click to expand...

If you have the defroster 'on', the fan will cycle as you mention when cold, btw.

TiRod said:

New caps cannot be the lever kind - they don't suck. Are you using the plain two ear or coffin style?

I ran a lever cap for years fighting a overheat problem, and found it contributed to a loss of coolant getting back in.

Click to expand...

Uhhhhh......
Strange....
Iam useing one of those and have no problem with over heating. my system works fine.
just my 2 cents.

Ronbo said:

If you have the defroster 'on', the fan will cycle as you mention when cold, btw.

Click to expand...

well that's interesting.. and redundant. i usually always leave it on defrost and low in any vehicle i've owned. I'll hook the fan back up and turn the switch for the heat to off and see if this stops the cycling.

i only had two short drives yesterday, not enough to get up to normal op temp, at least the level didn't rise or fall in the overflow in the last 24hrs.