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post #1 of (permalink) Old 06-14-2009, 12:47 AM Thread Starter
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CJ-7 Still Running Hot... Help Please!

I know it's a tall order to ask a CJ-7 in Arizona to run at normal temperature during the heat of day, but I just can't figure this out. Even when it's night time and in the 60's it will still start to run hot!!

Here are the symptoms:
1) The truck will idle all day at 185 now that the electric fans are in (a little hotter with the mechanical fan). That's even when it's 105 outside.
2) Driving through side roads and cruising around town (on 45ish mph roads) it will get up to about 210 degrees, but not higher.
3) On the highway it slowly creeps up about 10 degrees every 5 miles until I finally get to 230 and pull off, because it stalled once at about 240 a hellova long way from home. It started back up, but I had it towed anyway.

Here's what I've done so far (after all of this it still runs hot like I described):
1) Replaced the tiny little car radiator the previous owner with a 4 core SBC conversion radiator. The transmission is hooked up to the ATC that runs along the bottom.
2) Installed dual 11" Spal electric fans with a 185 degree thermostat that kicks them on, then off at 165. Had to remove the mechanical fan due to space limitations. They work flawlessly.
3) Replaced the thermostat, and I can see the temp drop for a short while right when that sucker opens. I know it works, but sure enough, the temp creeps back up.
4) Checked everywhere for coolant leaks, and there are none. Replaced all coolant hoses.
5) Checked for any kind of anything leaks... there are none.
6) Changed to synthetic motor oil (I'm getting desperate now!)

Any ideas are greatly appreciated.
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post #2 of (permalink) Old 06-14-2009, 01:18 AM
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You said it does not have any leaks.....but does it use any water....in other words, do you have to put any water in it say after 2 weeks? Water loss that you are maybe blaming to over heating?

If so....blown head gasket.....

Long shot....if the water pump is old the impeller blades might be erroded.

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post #3 of (permalink) Old 06-14-2009, 05:23 AM
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A few things to check - for free!

First check the electric fans to make sure the air is blowing the right way. That's a common mistake. You'd be surprised at how many get wired backwards. At idle they are fine, air moves OK, but driving at speed the fans counteract the air flowing in from the movement - results in stagnant air - no cooling.

I assume you've got a SBC in it? Fits tight, doesn't it? Make sure there's plenty of space around the engine to let the air out - you may have to trim splash panels or? If the air can't get out --.

Have you removed the upper hose, then started it to make sure the coolant is flowing - you should get a big flood as it drains the system. Sometimes the water pump's impeller comes loose from the shaft. Everything turns, but it's not pumping much.

The lower hose - look at it while revving the engine when hot. The lower hose is on the suction side, sometimes the hose collapses when hot at higher R's. There should be a spring inside the hose. Cheapie hoses don't, even quality hoses the spring can rust out or break.

And - if the spark advance isn't enough, or too much, it too can make it run hot. Make sure the timing idles about 8-10, and advances to a max of 35 degrees - with the vacuum advance connected. And make sure it's running on ported vacuum, not manifold vacuum.

Mixture - if it's running too lean it can also overheat. Look at the sticky posts on here to find "propane trick." It will tell you how to determine if it's way too lean at the higher speeds. It may be fine at idle, but at highway speeds it's way too lean.

Get, borrow or buy a laser type thermometer. look at different places on the radiator - to make sure it gets hot all over, not in just one place. You can also use it to find excessively hot spots on the heads too. Harbor Freight has them for about $30, Snap-On has the same thing for $200 or more.

An exhaust that's plugged or restrictive can cause overheating as well.
Look at the temp of the exhausts - they should keep reading cooler as you go from front to rear. If there's a restriction, like a crushed pipe or something stuck in it, that point will be much hotter.

Dual exhausts? With a crossover? If the crossover is in the wrong place - generally too far back, like behind the transmission and transfercase, it too can cause overheating. Instead of helping to scavenge the exhaust, it can actually "push back" the gasses, causing the heat to not get out. It all has to do with the pressure nodes in the exhaust.

Listen at the tailpipe while someone revs it up. Listen for a
"whooshing" or whistling sound, possibly an indication a restricted exhaust.

Try a vacuum gauge on manifold vacuum - it can tell you a bunch about how the engine and other things, like the exhaust, are working together. Everyone ignores the cheap little vacuum gauge as a diagnostic tool. For the money it's probably the best diagnostic tool there is. Simple and fast!

Let us know what you find.

Sometimes we fool ourselves - we get a "high performance" radiator - with extra fins and extra rows. They work OK at idle, but at higher speeds they won't let enough air get through.

There's a core that's more expensive but works much better. The tubes are bigger - and krinkled, and there are LESS fins on it. It holds much more coolant and the less fins allow much more air to go through it.
I put one on my motorhome - no matter what I did, I couldn't get it run hotter than where the thermostat was set. Before that core, it overheated on any excuse.
They use that type core on stationary engines and over the road trucks. Radiator shops ignore them 'cause they are more expensive and the mark-up isn't as much.
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post #4 of (permalink) Old 06-14-2009, 11:14 PM
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Originally Posted by kirk211 View Post
2) Installed dual 11" Spal electric fans with a 185 degree thermostat that kicks them on, then off at 165. Had to remove the mechanical fan due to space limitations. They work flawlessly.
What kind of shroud comes with these fans? Do they cover the whole radiator?

When I moved from Ohio to South Carolina, I developed a slight over-heating problem and went through all these issues too. I ended up adding a factory shroud with an electric fan installed in the middle of it. The shroud really takes the heat out of the radiator.
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post #5 of (permalink) Old 06-15-2009, 12:43 AM Thread Starter
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Hey, thanks for the responses. I just finished up replacing the rear brakes and changing out the fuel vent hose today... finally tracked down that slight whiff of gasoline smell! I've only had the Jeep a few months and I'm really liking taking on projects when I have time.

These are great tips and now I have a game plan for tomorrow. I'll let you know!

JeepDawg fortunately I haven't had to refill the radiator every few weeks, but now that you mention it I'm gonna keep a closer tab on that to be sure. I haven't really measured.

The water pump idea is a possibility as well. The engine is 31 years old and who knows how old the water pump is.

RRich thanks for taking the time to compile this list!

The engine is actually a Buick 350 - sorta weird. However, I like the distributor in the front which made for an easy cap/rotor/coil change. I still want to drop a Chevy 350 in later on. But for now, the engine runs really well and is giving me time to save up for the build up while still getting me to work. But that may change if it burns up on me!

Man, I hope I don't have to invest in an expensive new core... but what good is it to me right now with no engine if I seize the darn thing? The core has got to be cheaper than a new engine. The previous owner said he had no problems with the radiator, he had to sell it because almost nothing is stock on his crazy cool Jeep and it wouldn't clear his new steering box (which I noticed while wiping the saliva from my mouth was on the passenger side interestingly enough).

IN2DEEP the fan shroud does cover the entire face of the radiator. It's a great point you bring up because originally I was going to attempt to just get a fan shroud for the mechanical fan... but after some thought, nah, not enough. Then I thought about a mechanical and secondary electrical fan, nah, not enough room. So here I am.
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post #6 of (permalink) Old 06-15-2009, 01:05 AM
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The laser thermometer will tell you if you need a new core or not. If it's plugged the temp will only be hot in one or two places. Should be even all the way across it, and the lower you go down on it the cooler it should be.

I like the Buicks 'cause you don't have to cave in or modify the firewall for the distributor. I've had both.

Last edited by RRich; 06-15-2009 at 02:11 AM.
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post #7 of (permalink) Old 06-15-2009, 02:21 AM
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I have to agree with Rich on a bunch of this...

Buicks had a TERRIBLE habit of cavitation and corrosion problems with the impeller on the water pump.

Cavitation and corrosion will lead to an impeller not working as well as it should, so I would check flow through the pump.
(Or just install a good quality NEW pump instead of a 'Remanufactured' pump.)

Personally, I think it was a design flaw in the housing entrance that allowed for cavitation, but I can't prove anything...

The quick way to check for cavitation is to watch the water coming into the radiator tank through the radiator fill/cap hole...
If you see a bunch of bubbles coming in with the water when you Rev the engine up,
You have a cavitation problem...

Go back and do the obvious things again!

Make sure the radiator hoses don't make big high arches to the heater so they don't circulate air in the system...

Make sure the radiator cap is doing it's job!
You would not believe how many radiator caps and thermostats don't work correctly from the 'Factory' since everything is imported now with no quality control!

If the system doesn't pressurize correctly, you WILL overheat!

Make sure you use COOLANT MIXTURE and not plain water!
Coolant mixtures don't cavitate as easily,
It doesn't corrode the pump and internal parts,
And it makes the water in the system move heat more efficiently.

Use cheap distilled water without calcium, lime or salts!
(Water softener water is full of salts, so don't use it either!)

One test I would do is to leave the radiator cap loose (no pressure) and take the thermostat out of the engine completely...

Try driving it that way for a while...
If you still overheat, it's a VOLUME problem,
Either the radiator isn't letting enough VOLUME through to cool down,
Your pump isn't displacing enough VOLUME to do the job...

Something else I would check,
Water pump pulleys.
Sometimes, when engines overheat, people put on little pulleys to turn the pump FASTER....
And all they do is rip holes in the coolant (cavitation) and then they wind up with a 'New' water pump that doesn't have an impeller that will move water anymore.

You simply would not BELIEVE how many backwards turning fans I've seen down through the years!
"Drives GREAT in town, but when I get out on back roads or highways, it over heats, and we've tried EVERYTHING..."

Usually the fan on backwards...
REALLY common with electric fan installs when people switch from mechanical to electric...

If you don't use a shroud, you should just take the fan off and throw it away...

In the lab, on the dyno, PUSHERS work better than Pullers.
On the highway PULLERS work better and more reliably than PUSHERS.

So Many Cats, So Few Recipes...
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post #8 of (permalink) Old 07-04-2009, 03:56 AM Thread Starter
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Question Darn it!! Still running HOT!

Sorry I don't post often, busy at work lately.
So here is the latest:

I took the water pump off to check to see if the impeller was any good, because judging by the outward appearance that thing was old. I got it off and looked at it carefully and noticed that the impeller has been turning the wrong way this entire time. Eureka, I thought! Since I spent the time to get it off, a new one wasn't that expensive, and I couldn't be absolutely sure it wasn't slipping or something I decided to just put a new one on. While I had the water pump off I hooked up the power washer and was thinking I might see a big wad of crud come shooting out when I sprayed out the top and bottom holes where coolant travels. But no... clean. Then I cleaned the contact areas thoroughly and lined it with some coolant system approved sealer and slapped the new one on there. I had to order a double V belt from a tractor supply store (made by Gates Corporation) so that I could make the water pump turn the right way. I was hopeful that this would fix my overheating problem... but nope, virtually unchanged.

Not that there are millions of Jeeps out there with Buick 350's but this is something you may want to consider about your Jeep (or car for that matter) if you do have a Buick 350. Take the water pump off and manually turn it. If it's like mine the water pump impeller is designed to turn counter-clockwise while the crank turns clockwise (be sure you imagine the way it must turn when actually attached to the engine, not just in your hand). You have to run the BACK of the belt to the water pump in order to accomplish this, and the only non-ghetto way of doing that is by buying a double sided V belt. Size AA fits exactly, but they are sold in only hugely long lengths, so I had to buy size BB and trim off the little ridges on each side with an exacto knife. It fits great. You can bet that before I went through all this bologna that I was good and sure which way it was supposed to turn! Just a little tip I stumbled upon. This may be why I have seen in several posts people really having problems after buying water pumps at auto parts stores for the Buick 350.

While I had it apart I checked the upper and lower radiator hoses. No leaks, like I mentioned, and both have the integrated spring. They are in pretty decent shape, and the lower hose doesn't collapse on revving the engine. Notably, the upper hose doesn't arch really high to let air into the system. But to be sure...
I drove the front tires up on the curb to be sure the radiator was the highest point and added coolant mix until it was full to be sure there was no air anywhere in the system. There are no high arching loops of heater hose to/from the heater core. I was hoping this would allow the system to pressurize better, but it made virtually no change.

By the way, will it do any harm to take out the heater core and just cut the hose really short and bypass it? It basically is just heating up the passenger compartment even more than the overheating engine already does. The heater housing is all broken and rotten and useless, and the knobs to operate it are all stripped and crappy anyway. I'm just wondering though, does the heater core act like a mini radiator?

I built a fan shroud from sheet metal. I cut out areas for the power steering pump, the alternator, and 1 hose, but the rest of the shroud stretches to within about 2 inches of the block on all sides. Virtually no air heads out toward the wheel wells, and you can even feel a strong breeze at the rear of the engine compartment. I thought the shroud might fix the problem. Nope. Even after the sweet Spal dual fans blowing the wicked witch of the west back to Kansas, focused by a nice shroud it still overheats on the freeway, and will even get hotter at idle at stoplights (but if you ONLY drive on back roads, it won't get above about 210).

I thought this may simply be a problem with venting out the hot air. So I cut about a 2" X 12" rectangular hole in the firewall and vented the engine compartment out through the area where the A/C and heater (both long dead and gone) used to vent under that louver looking thingy in front of the windshield. I figured hot air rises and this was the highest part of the engine compartment. Don't worry, I kept the little trough intact with the drain tube that channels rain and snow out into the engine compartment. That way rain and snow can't just run in and onto the engine. I think doing that for the better part of 2 hours helped about... none. No change in the overheating problem.

I went out and bought a laser thermometer (only $30 at AutoZone if yer looking) and checked the radiator. Like you said it seems to be working properly because it showed about 140 to 150 all the way across the top and down to only about 100 near the bottom. No hot spots anywhere. It seems the engine is hot but the coolant is cold, how the hell can that be? It's 100+ degrees out today.

I ran the Jeep down the freeway again a couple of exits until I got borderline hot at 230 and pulled off. I left it running and jumped out and checked the hood temp with the laser, and hit the engine compartment with it too and neither was hot. Nowhere near 230. Then I started checking the exhaust and intake manifold (more on that in a sec) and in the 10 minutes I spent checking temps all over the place the temp cooled down to 180 degrees at idle. I revved it for about a minute just to see what happens, and it jumped up about 20 degrees, even with the hood wide open and the fans blasting. How can you get more ventilated then that? I bought some 3" by 10" fender vents but I'm highly suspicious they won't do a darn thing.

When I used the thermometer to run the exhaust from front to back I thought I found something interesting. Right under the cylinders gets hot at about 400 to 450 degrees but as you travel back down the headers it gets cooler as expected, right? However, on the driver's side just above the heat riser I noticed the temp was about 500, whereas on the passenger side in the same bend where the heat riser would be is about 400 degrees. So, I took the exhaust pipe off the driver's side and looked up in there. No visible blockage, and the heat riser valve is in the open position. With the exhaust back together I started it and walked back to the back and it feels like the same pressure is leaving the pipes on both sides. The exhaust pipes just run straight back with no crossover. Then for giggles I ran the engine until it got hot again at about 230 and looked at the heat riser to see if it moved or did anything weird. It stayed the same. Just to confirm for my own sanity, the heat riser is open when the arm from the thermostat is fully extended toward the front of the vehicle, right? I grabbed the lever that the arm attaches to with plyers and it seems to move fairly well when you give it some good force, and it returns to the same place. Seems like the spring is working. Guess it isn't the heat riser????

I adjusted the carb air/fuel mixture richer until I got it running so rich it stunk up the place and ran like crap, then backed it off just until it ran okay. I drove it and it still got hot. Guess it wasn't running too lean????

The timing has been adjusted with the light and is good. No change in overheating. Guess it isn't the timing????

I checked the expensive ass synthetic oil I put in it and it remains topped off and very clean. That isn't helping much either.

I even hit the heater core with the thermometer and it reads in the 140s. What the?

Any more ideas?

Guess I move on to the vaccuum guage? Can you tell me how to interpret the numbers I get? I don't know really what I'm looking for because I have never used one.

Thanks to all of you who are better at this than me and taking time out to help me. I feel like some super stud mechanic would be able to figure this dang thing out. Know anyone in the East Valley of Phoenix?

I really like working on the Jeep, I just am ready to figure this darn overheating thing out already and move on to other projects!! I just wanna drive my cool ass old beast to work every day. HELP!!!!

Last edited by kirk211; 07-04-2009 at 03:58 AM. Reason: Forgot something
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post #9 of (permalink) Old 07-04-2009, 07:12 AM
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You sure seem to have given the cooling system the full monty. The only thing I can think of is a leak from the combustion chamber into the cooling system - either a cracked head or a blown head gasket. And yes, the heat riser butterfly should be open as soon as the engine is warmed up.

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post #10 of (permalink) Old 07-04-2009, 10:55 AM Thread Starter
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What are your thoughts on taking out the heater core and bypassing it? Will it make any difference in cooling?
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