'87 YJ high water temperature problem-

duckkillerclyde

duckkillerclyde

New member
'87 YJ 4.2

Problem;
Water temperature will run too hot. Since I've had it, the water temperature gauge has run ~210*. Now it will like to run much higher and if I run her 'hard' it will darn near reach the red.

Less than 2k miles ago, I replaced water pump because it was leaking. I know the pump is pumping the correct direction as we went through this at the parts house. Fan belts are tight and it good working order. When I did the water pump I had the radiator boiled out and repaired a minor leak. The radiator and water pump are in good working order.

This leads me to believe thermostat. I should have replaced it when I had everything else apart but didn't think about it at the time. There is no water in the oil or oil in the water. I do not believe the head or head gasket have failed.

What do you think?
 

Replace the thermostat. Usually if the head gasket fails you will have white smoke coming out of the tailpipe at startup, then it will diminish after the engine warms up. The other way to check for a blown gasket is to use a meter to check for gases in the antifreeze. Also, did you change the hoses, they could be collapsing on the inside restricting flow.
 
Catoctin Jeep said:
Replace the thermostat. Usually if the head gasket fails you will have white smoke coming out of the tailpipe at startup, then it will diminish after the engine warms up. The other way to check for a blown gasket is to use a meter to check for gases in the antifreeze. Also, did you change the hoses, they could be collapsing on the inside restricting flow.
Click to expand...

Changed bottom radiator hose, the other ones looked fine and were very easy to get to so I left them. I will check them tomorrow. Do you recommend using a lower temperature thermostat? I live in a very mild part of the country, rarely gets really cold and rarely gets very hot. I am also hot so if the heater doesn't work as well that's no big deal to me.
 
I have used lower temp thermostats in none fuel injected engines with no real ill effect. I'm guessing you have a 4.2 liter, so I believe those engines are not fuel injected, in that case you can do it. If it is fuel injected I would stick with the stock temp thermostat so not to through off the computer which could make the air/ fuel ratio richer decreasing fuel milage.
 

I'm not fuel injected. Thanks for the help.

Anyone else with comments or suggestions, feel free to speak your mind.
 
What temp thermo do you have? Usually thermos fail open, or stick.
Eventhough you have cle anec the radiator is the exterior fins clean?
Do you have anything blocking the radiator or directly in front of the radiator?
Is this when idling or below 35 mph? Or while above 35 mph?
how is your fan? Do you have a fan shroud?
 
JPNinPA said:
What temp thermo do you have? Usually thermos fail open, or stick.
Eventhough you have cle anec the radiator is the exterior fins clean?
Do you have anything blocking the radiator or directly in front of the radiator?
Is this when idling or below 35 mph? Or while above 35 mph?
how is your fan? Do you have a fan shroud?
Click to expand...


Don't know what temperature of thermostat I have. I am assuming 210.
Exterior fins are clean on radiator and nothing is blocking it.
The heating problem only occurs while driving above 35MPH.
Fan looks to be in good working order.
Yes, I have a fan shroud and it is in good working order.
 

Dont know if this is your problem or not, but if your radiator hoses are the type that dont have a spring inside it, over time they can get soft in the bends mainly at the inlet and outlet of the radiator or engine and suck themselfs shut. It will do this as engine speed increases. I have been able to rev the engine and see this before, and is more common than you would think.
NEVER MIND, JUST SEEN YOU ALREADY DID. COULDNT ERASE MY POST.
 
Your thermostat should be 195. Flatie46 has a good point. Check the fan clutch. Grab the tip of the fan and wiggle back and forth to feel if you have play.
 

Above 35 mph there should be enough air through the rad to sufficiently cool the fluid. So it isn't your fan. You likely have a flow problem, given the rad is clean inside and out. And you have all the air out of the system. You may need a new thermo.
As mentioned the lower rad hose should have a spring to help to keep it from collapsing.
You could also have too much circulation. What type of water pump did you put in? High flow water pumps could actually circulate the coolant fast enough to not allow the heat to be absorbed by the fluid and released by the rad when the thermo does open.

Did you use the correct coolant and mix it with distiller water?

Did you flush the engine? How about your heater core? Got heat? Your heater core is a part of your cooling system and if blocked your coolant isn't circulating correctly.

Personally I'd burp the air out and see what happens. Possibly rev the engine to above 3000 rpm while at temp and inspecting the lower rad hose to see if it collapses when the thermo opens.
If it continues flush the system and replace your rad cap witha new stock 18 lb cap.
 
Last edited:
JPNinPA said:
Above 35 mph there should be enough air through the rad to sufficiently cool the fluid. So it isn't your fan. You likely have a flow problem, given the rad is clean inside and out. And you have all the air out of the system. You may need a new thermo.
As mentioned the lower rad hose should have a spring to help to keep it from collapsing.
You could also have too much circulation. What type of water pump did you put in? High flow water pumps could actually circulate the coolant fast enough to not allow the heat to be absorbed by the fluid and released by the rad when the thermo does open.

Did you use the correct coolant and mix it with distiller water?

Did you flush the engine? How about your heater core? Got heat? Your heater core is a part of your cooling system and if blocked your coolant isn't circulating correctly.

Personally I'd burp the air out and see what happens. Possibly rev the engine to above 3000 rpm while at temp and inspecting the lower rad hose to see if it collapses when the thermo opens.
If it continues flush the system and replace your rad cap witha new stock 18 lb cap.
Click to expand...

I just put in a new OEM style pump. My Jeep is not a fancy one, it is just a car that happens to be a Jeep. Heater works. Maybe the core is partially plugged but I doubt it because the radiator didn't really need to be boiled, the guy that fixed the leak in it did it as part of the service when I got it repaired. As far as the coolant goes, I'm probably at least 3/4 gallon ahead on anti-freeze.
 

The one thing that seems to haven't been checked is the temp. sending unit.. It could be giving you an improper reading. Just a thought..
 
Radiator hoses do not appear to collapse at higher RPM. I believe the temperature gauge to be in good working order.

I will be replacing the thermostat either tomorrow or on Sunday or on Monday. I'll try to post back with results.


Thank you for all of the replies.
 

Maybe I don't really know what I'm talking about but I've had my cooling system checked and the flow is OK, the FlowKooler is only flowing more coolant than stock at slower speeds as I recall. At highway speeds they're equivalent to stock flow rates. Perhaps these are false claims as I've seen many, many posts bashing these FlowKoolers but it seems the issues I've had have more to do with an inadequate shroud/e-fan assy.

Hi Flow Water Pumps that end overheating, Quality Jeep radiators and off road custom radiators for J | FlowKooler Automobile Water Pumps - Chevy, Dodge, Jeep, Ford, and more
 

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.
 
You must log in or register to reply here.

Similar threads

bradleyheathhays
1st transmission problem in 28 years
Replies
1
Views
279
superj
superj
TerryMason
LED lights (brake, turn and maker) for my Jeep TJ
Replies
3
Views
2K
JPNinPA
JPNinPA
J
Tire size & rim compatibility on my 87 YJ
Replies
0
Views
4K
jhigh47
J
B
Coolant leak near battery?
Replies
5
Views
7K
JPNinPA
JPNinPA
G
Overheating and startup issue
Replies
1
Views
5K
JPNinPA
JPNinPA
Back
Top