normal temp for stock 4.0

I run just under 210 normally. Is this too high. Can I bring it down? Its a 98. Electric fan cycles constantly.

This is normal. You don't need to bring it down. If it climbs much above 210, that's when you can start to worry.

Willboy,

If you are worried then as an experiment change your thermostat. Go to the dealer and buy a 195F, guys on here say the aftermarket ones lack the vent hole. Also Chrylser "has to" sell parts that work the after market sell parts that usually work. Considering the importance of a thermostat I'd spend the $8 for the OEM one.

My radiator shop told me if you get the thermostat to 225F one time you can damage it. Have you had your XJ get hot?

Also you are at the age the mechanical fan clutch could be at the end of it's life. For peace of mind I'd install a new fan clutch. When you pull off your old fan clutch take it with you to the parts store so you get one that looks like it. Some aftermarket clutches are much bigger and require you to tilt the radiator to install - not for me.

If you have been the owner of the XJ since it was new are you still running the factory hoses for the radiator? You may want to change the hoses and coolant. I have adopted a 4 year cycle on radiator hoses.

Then to top it off if you're this far into it put on a new fan belt. I believer in changing them every 4 years also. I had one break on my XJ but it was given to me through my Dad's estate. I ended up over heating the vehicle, I concluded the belt was 12 years old when I changed it. So a vehicle I thought was good bit me.

So you can do nothing or you can do:
1) Thermostat
2) Fan clutch
3) Radiator hoses, coolant & radiator cap
4) Fan belt

HTH

Martin

210 is normal. No need to worry unless you begin to overheat consistently.

That temp is normal, but.......

The constantly cycling fan worries me. What does 'constantly' mean exactly? How often and when? As i posted on here recently in a rad thread, since i installed the UC two core OEM alum radiator, my elec fan has yet to come on once on my '98. Even with the old radiator it did not cycle quite like you seem to be indicating, unless the A/C was on then it is normal to come on with the compressor.

The damage to the thermostat is around 250 degrees. I also would do the OEM on that-

Judd,

I don't know where you got your information on 250F is the minimum temperature to damage a thermostat. I was told ths information by American Radiator which had been in business for 50 years in St Louis. When you walked in the place had the smell of antifreeze soaked into the concrete. You know, one of those places that the neighborhood has changed, they have fences and lockable gates with barb wire but does a land office business because they know their stuff.

I never mentioned this before but the guy told me to change my thermostat after my overheat and did not even try to sell me a new thermostat. So him telling me tht information cause him to make a sale.

Before I had talked to him I was thinking like you that a thermostat should be able to 250F for a short period of time with no problem. He insisted that seeing 225F one time, even if it is a short period of time, can damage the thermostat. Why would I doubt the guy, cooling systems "is his business".

After my overheat due to a broken fan belt I was getting wider swings of the temp gauge and I was running at 210 vs the historical 200-205F I had been running. I was in the radiator shop to find out what a new radiator would cost, that when he told me how little it takes to mess up a thermostat.

I just want guys on here to know to consider the thermostat when they have cooling system problems, it is a part that gets overlooked.

Martin

one more thing:

Changing the thermostat with a Mopar 195F one solved my temp swing problem. Also I mistyped when I was trying to say the guy did not even sell me a thermostat and he tried to keep me from replacing the radiator when he thought a thermostat would fix the problem.

I can attest to what Martin is saying. My XJ was in the shop all week getting new paint, so I borrowed my Father-In-Laws '96 Ford Ranger for the week. Tuesday morning on the way to work it started to to run hot - every few minutes the check gauge light would come on and the temp gauge was pegged just short of boiling.

My F-I-L and I talked about it. He said thermostat but I suspected water pump.
The car had next to no power and the auto was shifting very erratically.

Well, I went to FORD and bought an OEM thermostat for it (cheaper and easier than a water pump!). I put it in on Friday morning, and the temperature went back to normal, the engine power seemed to be more like a V6 4.0L, and the tranny shifting smoothed out.

So, first job - new thermostat - could be just the ticket.

Martin......

I certanly hope the 250 temp i have heard for quite some time is the, or near the real honest damaging temp. For an example these XJ's normally run in the 210 temp range and may very well hit 220 really quite easily!! That is awfully close to the 'stat damage range in normal use!! Would hate to think it is that sensitive!! Know what i mean?!

Martin,
That 225* max may have been used in the past when engines operated at 160* to 180*.
Newer engines are designed to run much hotter that those 50 years ago. Normal temp for a 4.0 with 195* thermostat is 210*,the aux fan is switched to come on at 218*.
I sometimes wonder what the difference is between the temp sensor at the thermostat housing and the guage sensor at the back of the head ?
It would make sense that a reading at the back of the head would be higher.

Wayne

Guys,

I am just trying to pass on what I have picked up for the years trying to maintain my 88 XJ. I think I said in my first post if you see 225F it "can" not "will" damage the thermostat.

One of you guys who has the test set should hook it up and go driving, compare the temp gauge read out to the diagnostic tool to see what the computer says what temperature it is running at.

I had a course on sealants and plastics and for some reason most any sealant will stand up to 180F without a problem, but there are very few sealants that stand temperatures greater than that and even fewer at temps greater thatn 212F.

What I understand about thermostats is there is a bimetalic spring which opens the valve when the correct temperature is reached. The way you adjust when it opens is changing the thickness and or alloy used in each layer of metal in the bimetalic strip. Now for emissions/improved MPG reasons engines run hotter to get better thermal efficiency.

For discussion lets say our coolant is good old water. At 225F water has a value of 196 BTU/lb while steam has a value of 1155 BTU/lb. If you have an over heat good chance the themostat will see "steam" and that additional heat could do damage to those internal components of the thermostat.

I think we all agree when you need a thermostat go buy it from the dealer. So next time you have an overheat remember the thermostat and radiator cap. One makes sure the coolant flows at the right time and the other one makes sure pressure is in the system so you don't over heat.

In my experience it is the simple things that get me so I try to keep up on my maintenance. Considering what we spend on other parts for our XJ, thermostats and radiator caps are cheap to change. Rather spend $10 to $20 to make sure I don't cook the engine even though it cast iron.

We are lucky we don't have aluminum engines, one overheat and we'd be talking engine replacement. My buddy with a northstar in his deville and was telling me how critical cooling system temperature is and that why it has 7.5 quarts of oil that circulates through the radiator so the oil can also act as coolant if the cooling system can't circulate it's fluid. If that happens the computer goes into a limp home mode.

Be glad we can work on our vehicles.

Martin

martin said:

I think we all agree when you need a thermostat go buy it from the dealer. So next time you have an overheat remember the thermostat and radiator cap. One makes sure the coolant flows at the right time and the other one makes sure pressure is in the system so you don't over heat.

Click to expand...

Minor nit-picking correction:

The thermostat does control when the coolant flows to/through the radiator. With that I agree. However, the radiator cap does not prevent overheating. It cannot. What it does is raise the pressure in the system above atmospheric pressure so that WHEN you overheat, the coolant remains in a liquid state rather than converting to steam. In other words, the pressure cap raises the boiling point of the coolant.

Eagle,

We both said the same thing, I said the cap makes sure you have pressure so you don't overheat. If we ran without a radiator cap or a defective one that did not hold pressure and only used water in our colling system then we would have the coolant flashing over to steam once you reached 212F at 1 atm pressure.

With a 15 psi cap installed the boiling point of water is around 250F.

With our 195F thermostats I am sure portions of coolant get to temps hotter than 212. So with no radiator cap installed we would have steam inside the engine, this would cause some of the water to go through a phase change and turn into steam. Once the water is converted to steam there is an increase in volume which would cause a boil over. To me a boil over would be the over heat I talked about since the process would continue until there was no water left in the cooling system.

The key is having a radiator cap that holds pressure in the cooling system so the boiling point is raised so phase change of the coolant does not happen.

Martin
Martin

Talking about coolant flow......

One interesting detail i have mentioned on here in the past is how the temp gauge on my '98 reads lower, maybe 10 degrees lower, when the heater hose is clamped off... that is ~190. We are discussing some the varying temps at different spots in the head and this adds another dimension. I tried this to see if totally cutting off the flow of coolant into the heater box increased the efficiency of the A/C. Many vehicles do this, ours do not.

Dealer ONLY Radiator Cap?

Just wondering why there is an empahsis on Dealer ONLY? I always use a brand name like Stant. Current unit is NAPA and the only thing I do is drill a 1/16" weep hole and clock it at 12:00 when I install. Am I missing something about this Dealer ONLY thing?