[1869]

I have the original 258 in my 81 CJ7. there are about 100k on it. My problem is that the temperature gauge nears the "H" when I am on the freeway, but when I slow down around town it goes right back down to the mid range of the gauge. It also is 6 degrees below zero here now and this is still happening the same way it was when it was 50 degrees out. I just replaced the thermostat tonight with a 195, and it is still happening. After a ten minuted drive the gauge was high, I got out with the engine running and I could hold my hand on the radiator hoses and radiator and they were only warm/hot. I could also touch the block and head and hold it for a few seconds before it became uncomfortable.
It is possible the temp gauge/ sender is not working correct, but why would it get hotter on the freeway, especialy in sub-zero weatehr, but cool off around town. I run approx 2500 RPM at 60 mph. Also it has the stock fan, no fan clutch, and no fan shroud. maybe my water pump is going bad and cannot keep up with the high speeds?? any info would be great.

 

[2615]

I've had radiator hoses collapsed at higher speeds when the water draw was higher and I had a waterpump that the impeller blades were rusted off of too. Whens the last time the radiator was flushed out or serviced?

 

[1869]

I just replaced the radiator hoses when I did the restoration this summer, but that is someting to look at. As for the radiator, I left it alone. It was new in 92 or something like that, so it is old, however the jeep wasn't run much since then also, maybe 10,000 miles at most. looing in the radiator I can see some buildup around the openings of the rows, but not so much that I would think it would affect flow greatly, maybe thought. thanks for the ideas. Also I dont have a winch or anything else up front that would hinder air flow.

 

[2615]

Is it possible that the belt is slipping at higher speeds?

 

[1869]

Interesting you metnion that. I was just out in the garage to check that and it appears to be very tight. I actually can turn the fan by hand with moderate force and as a result turn the engine over. Is this normal, or do I have really low compression?

 

[171]

You might want to throw a mechanical gauge on it or a different one..
If the Radiator was replaced , was it replaced with a bigger one ...this will sometimes cause overheating as the water does not spend enough time in the radiator to cool.
Warm it up with the cap off and see if the water starts flowing when it reaches Temperature.
Ignition timing couldn't be too far advanced could it ?
Put a shroud on it ...4 wheel drive hardware sells them or get a generic one.

 

[Jim_Lou]

I think Greenboy will win the prize - water pump.

 

[Guest]

Sounds like what happened to me. On the trail, I noticed it was running a little hotter than usual. When I went home, it started getting hot at 65 MPH. Backed off to 45 and it cooled back down some. My problem was the radiator was partially plugged. Had it cleaned and it's been fine ever since. Hope this helps.

 

[1869]

Here's what I did this morning and still no results. Today I went into the shop and replaced the water pump (with the correct normal rotation one required for a "V" belt), however the water pump I took out looked fine. I put a new radiator cap on, and made sure that the lower radiator hose was solid and was not collapsing (I replaced it this fall so I cant immagine it would be bad anyway). After I filled the cooling system back up I unscrewed the temp sensor with the jeep running and I had coolant spraying out, so it is getting through the engine and verifys there is not an air pocket trapped by the sensor. I did notice that the lower radiator hose heated up much sooner than the upper one (this is probably normal however). I am ruling out a blown head gasket (as long as I dont drive it with this problem

There is no abnormal smoke from the exhaust other than what you see in cold weater. Also the oil is nice and clean, no evidence of coolant in it. So Im thinking radiator?? I found someone that can flow test it so that will be my next step I guess.

any more suggestions????

 

[027]

In reply to:

but why would it get hotter on the freeway, especialy in sub-zero weatehr, but cool off around town.

[/ QUOTE ]

25% to 40% blocked radiator will do just that.

Take you radiator off the Jeep, (costs less that way) and take it to a radiator shop have them pull the top and bottom caps and rod it.

I had this same thing happen to me and after replacing every thing BUT the radiator on the cooling I took it to a shop and even though it looked clean where I could see it when the caps were pulled I had a 40% blockage. cost me $50.00 and no more problem. The reason it heats up on the highway and cools off in town is you are heating faster at highway revs than at the lower in town revs.

 

[1869]

this afternoon I took the radiator out of the jeep and took it to the radiator shop. They flow tested it and said it was just fine. I watched and water was flowing very rapidly through the radiator, much faster than I can immagine it would ever be on a vehicle. My gauge still reads very high and now it seems to run high all the time, regardless of wether I am on the freeway or around town. I will get a new temp sensor tomorrow and see what that does. IF that is the cure at least I will know everything I just needlessly replaced should be good for a while

I also wanted to add. If the upper radiator is hard (pressurized) does this meant that the thermostat is open and coolant is flowing through the hose, or is the thermostat closed and the pressure is building up until it opens. I ask because after one of the quick tests today the upper was fery hot and solid right after I shut the jeep off. Then I started it up and let it idle for a while and the upper hose got softer.

 

[Dirt Dog]

My $.02

I still think it's the radiator. Flow tests mean only about 30% of the total.

Which means it can still flow great, but not transfer the heat.

Q#1 Did it start all at once?
#2 Are you geting heat out of the heater when it gets hot?
#3 Are there any remote signs of a blown head gasket? (water in the oil, excessive "funk" on the oil cap-thats new)

Just a start.......I think we can figure this out.

(any possibility you can borrow a rad to try?)

 

[1869]

If it is the radiator luckily it's a Modine, which I believe have a lifetime warranty. I have the recipt from the previous owner instaling it, hopefully that would be ok. The fins for the most part are intact and not bent with a few rusted ones on the outer edge and some bend ones from road debris, ect. I found out how to read the temp sensor with a voltmeter/ohm meter. I will try that tomorrow and see if the ohmmeter readings correlate with what the gauge says.

Like I said earlier I pulled the dipstick and the oil looked nice and clean. However I jsut went and pulled the oil cap off and the inside of the cap as well as the edges of the oil hole are covered in a tan/ milky brown substance, but still no sign of that on the dipstick. If I do have a cracked head or head gasket the jeep sure runs surprisingly well. I mean it doesnt have near the power of my k5 blazer, but never did and all my buddies have v8-s in their jeeps so I have no comparison.

If I have a cracked head or gasket will I be able to tell by looking at the plugs, would one or more be discolored? what color would indicate antifreze getting in the cylinder?

 

[1869]

I borrowed a noncontact thermometer from a friend tonight. I got the jeep up to operating temp and then used the gun to search for hot areas on the block and head. It uses a lasr beam to relay the information to the handheld device and at aobut 12" it is about 95% accurate. I was reading temps of 250 near the temp sender on the top of the head and other areas along the top of the head I had temps of 220- 250. all other areas of the engine were much cooler, 120- 170. Except for the exhaust manifold of course which was 450. So should the head be this hot near the temp sender? the coolant should be cooler than the metal cause thats why it is there, to cool the metal. of course I wasnt driving eaither, just idling and at times holding the throttle at aobut 2 grand to heat it up a bit. I will know for sure tomorrow weter the sending unit is good when I do the conductivitiy test.

 

[Jim_Lou]

In an earlier post you said that the lower hose got hot before the upper hose. Normal flow is hot water past the thermostat through the upper hose and into the radiator, then down through the radiator, cooling on the way, then cool (relatively) water through the lower hose back into the engine.

I've never looked at an engine with a non-contact thermometer, but the readings you get seem reasonable.

 

[Dirt Dog]

Since you have use of the IR thermometer, let me know you you need "baseline" readings. Since I have one I can shoot mine in different areas to compare them if you don't end up figuring out your problem right away.

 

[Guest]

We were trying our dardest to figure out the same thing in an '80 Eagle with the 4.2L (258 CID.) Car would overheat at random on the highway, never around town. Some days at 110 degrees outside it was fine, other days it would overheat. Same thing would happen when it was cold... it didn't matter.

Turned out it was the radiator... it had a small pinhole in it that would let in air, causing a bubble to form somewhere inside the engine... and disrupting flow. Oddest thing, it wasn't leaking water, it was letting in air.

Anyway, replaced the radiator with a fresh rebuild, and it was fine after that.

I had the radiator in my '82 SX/4 done a year ago (tanks removed, rodded out, re-soldered and painted) for about $90. I'd find a good local radiator shop, it might be cheaper to have them recondition your existing radiator instead of buying a rebuild / new, if the warranty angle doesn't work out.

 

[1869]

Ok. so I just OHM'd out the sensor and the values I got were consistent whith information I got off the internet on what should be expected for each area of the gauge. I also used the non contact thermometer again and here are the readings.
On top of the head next the the valve cover I had readings of 160 to 200 (getting hotter towards the back of the head)
Between the spark plugs on the head I had readings of roughly 150- 160 consistently. Both sets of readings on the head were taken when my gauge was at about the 3/4 "mark" between C and H.

For a reference where should the needle on the gauge be on a 258 that is operating normally? I always figured right about at the 1/2 area.

Now I am thinking that either there is a small crack or head gasked leak, or there might be a blockage in the cooling system. Would a cooling system flush clean out a blockage?

Also, thanks to everyone so far for the replys and advice!

 

[Guest]

This may be outta left field but... Could it be caused by a pluged cat. I had that happen to my 87 YJ and it caused overheating. Exhaust no getting out and all that. Just a thought.

 

[1816]

What is the difference in tank temps? The lower rad tank should be atleast 10* cooler then the top if the rad is doing its job. You may want to do this sitting still and then test it again after you run down the road after the temp climbs.

Also warm it up good and feel the core for cold spots,be careful of the fan. If you get cold spots the rad is plugged. Most of the cooling comes from the center of the core. The flow test can be miss leading and only show bad if the rad is almost all plugged.

You may want to take a look at the thermostat too, I know it is new but you can get junk in a box. I just went through it with one. Also if it is one of those superstats throw the thing as far as you can and get a plain old thermostat.