'87 YJ high water temperature problem-

[JPNinPA]

Wouldn't it do this one it's own in the overflow reservoir?

Nope! With the engine cool take the radiator cap off and jack the front of a jeep up, or park on a hill. Start the engine and watch for bubbles in the radiator. When it comes up to temp and the thermo opens there should be a number of bubbles comming out. When the bubbles stop after a min or so, top it off and put the cap on.

Just a stab here. but I once had over heating problem and it turned out to be a bad radiator cap. To this day I dont understand that but I replaced the cap and no more over heating.

The radiator cap is a 2 way valve it holds the system to 18 lbs before opening and allowing fluid into the overflow. Once the engine cools the valve opens allowing the fluid back in due to the vac effect of the system from the cooling. Water boils at 212 in a open environment but the boiling point rises when held under pressure, so by holding the system to 18 lbs the boiling point is raised. Lower the pressure and the boiling point lowers.
So if your cap is not functioning and opening at a lower temp, it is like having a lower lb cap. This allows the fluid to boil at a lower temp.

 

[69jeepcj]

Didnt realise the boiling point rises under presure. Makes sense, thanks for explaining.

 

[duckkillerclyde]

I put a new cap on when I did the radiator. I still haven't put the thermostat in. :redface:


I don't drive her very often as I don't need to. (my job provides me a vehicle and fuel, makes it hard to drive my own)

 

[JPNinPA]

Was it an18 lb cap?

 

[duckkillerclyde]

put new temp sending unit and gauge in. That seemed to take care of my 'overheating' problem.:roll:

 

[duckkillerclyde]

put new temp sending unit and gauge in. That seemed to take care of my 'overheating' problem.:roll:

Nope.

Cut the catalytic converter out and she runs like a stripped assed ape now. No more overheating problem.

*I have two temperature sending units for the one gauge..... Had two gauges going at once. One would still get hot the 'new' one wouldn't.

 

[72rtchallenger]

if the timing is off can cause overheating , as it appears you have checked everything else,,change the thermostat and maybe try a good flush of the system , and as stated above a radiator cap can cause the issue as well,,and if its a high mileage motor I would rule out a water jacket clogged on the block or the head , and or something installed wrong that would block flow of the water,,also is it boiling over or showing signs of overheating or is the gauge only telling you this,,also is the fan shroud in place as this is an issue ?

 

[duckkillerclyde]

if the timing is off can cause overheating , as it appears you have checked everything else,,change the thermostat and maybe try a good flush of the system , and as stated above a radiator cap can cause the issue as well,,and if its a high mileage motor I would rule out a water jacket clogged on the block or the head , and or something installed wrong that would block flow of the water,,also is it boiling over or showing signs of overheating or is the gauge only telling you this,,also is the fan shroud in place as this is an issue ?

I've had the problem fixed for months now. I just couldn't remember my password to log on and I was too lazy to get a password reset.

The problem was a plugged cat.