HELP PLEASE!!!
1994 Disco I, 168K BAD HOT over heating.

While at idle, quickly overheats (within 30 minutes in 90 degree weather. Last week old black expansion tank cracked. Replaced with new white one from AB. Also replaced lower radiator hose. Truck still over heated at idle… less so when driving, but quickly at red lights. Did Chevy fan clutch conversion. Piece of cake. Still overheats…

With semi clear/white expansion tank now notice coolant boils extremely hot. When **** down can hear coolant boiling inside engine??? Inside radiator with fill plug removed… can see decent fluid flow. Not real strong… but would seem good enough. 3 years ago did exhaust manifold replacement. While doing that… had radiator boiled out and refluxed. So assume radiator is ok. Thinking maybe water pump but again see flow thru radiator and no leaks at water pump. AC works. AC fans come on when truck gets hot and when AC is turned on.

On business trip this week so wife takes Disco to friend of friend mechanic. Says he sees that boils and fast heat and pressure… suspects bad “internal” gasket. Does not know. Does not want to mess with the truck. Says job to big for a 1994. May not even fix problem? Does not want job he can not for sure complete or know do not knowing for sure what is wrong. Suggests I find someone who loves to work on these trucks. (only thing he said which made sense). Also said “those British cars” are not like American or Asian cars. They have different designs and are hard to understand (glad he passed on the job).


So what could this beast be? Internal gasket of some kind? Truck oil just changed… no water or coolant there. Coolant color on new coolant is good… no oil there. No white smoke when accelerating.

Could the water pump just be passing water but not enough yield? Have seen radiator flow before on other cars… this one not as strong as others I have seen… but not to shabby. With towel if I squeeze upper radiator hose… can see coolant fries and fall inside new expansion tank. Oh BTW.. removed thermostat… so that is not it. The upper radiator hose is pliable… not as firm and full of fluid as I have felt on other cars.
Any suggestions thoughts???

Thanks

joe

 

You are running with no t-stat? Not a bueno idea. I would replace that right away. Not saying that's your problem but definitely not good for your truck. Good luck. I have fought a very similar overheat problem for a year.

 

Lets start from the top.

From what you have said - this happens at idle or slow speed, not while underway. Underway you have plenty of air flow to take away the heat created by engine working hard. Water pump must be hanging in there, or you would have problems at both speeds. Thermostat is out of the loop, because you removed it. The stat's job is to control how cold the engine is, if it sticks open water won't stay in the radiator as long as it should to cool off. If it is removed, it can't let water stay in radiator long enough to cool off, so put a good one back. If it sticks closed, yes overheat real quick. If you allow it to slip down when installing, it can have a 1/4 inch wide arc above it and behave like a stuck open stat. You said you replaced the fan clutch- check the belt route, if wrong the water pump can run backwards, and can't move as much water - see internal photos of impeller.

There is a plastic or metal plug on the battery side of the radiator. When cold, you can remove it and peek inside with a flashlight, may see calcium buildup on tubes. If you had it rodded out when it was boiled out that may not be a problem. Hope you have been using distilled water and coolant. Replace plastic plug with $2 brass 1/2 inch NPT from hardware store, plastic ones will break. Should be able to see through radiator fins with light, no clogs from mud. Inspect area between radiator and condenser for trash trapped in that space. You can also top off the radiator via this plug, and massage the upper hose while adding more coolant to the expansion bottle. You want to get out any air trapped in the system. May need to have radiator serviced again, my indy shop charges $65 (acid boil out and rod out), and says a good radiator should be within 10 degrees across the surface.

Now to the fans. You did the chevy clutch conversion, which I also did. Are curved sides of blades facing engine? When cold, is clutch still firm, can't spin fan more than a fraction of a turn? With AC off, truck engine cold, crank up and you should hear a "roar" of fan noise as it is coupled at 75 - 80% power. In a minute or two it will drop down to 20-30%, and noise decreases. On mine, the blades of the AC fans spin from the air being pulled in by the radiator fan. Take a skimpy plastic bag and hold near the grille - it should pull toward the radiator, not blow away. If there is a blockage in the radiator or in front of the radiator, hot air can't get to the fan clutch surface, and it needs to be 170 degrees to start "coming back to full power."

Repeat this test again, this time with engine off, switch on, AC on, inside fan on. The two electric fans should come on and run. And they should also pull the plastic bag toward the grille. My PO reverse wired replacement fans - and mine would overheat whenever at idle with AC on.

Has coolant level been dropping? Have you heard "gurgling" sounds inside the dash from air pockets moving through the plumbing? Could be head gaskets allowing combustion gas to enter coolant. There is a chemical test for this you can buy at the auto parts store. A lot of posts on this forum indicate a fair market price of over $1000 for a head gasket job. But you can buy kits of the parts, which include new head bolts.

With a 180 stat or a 195 stat I can idle without overheating, now that my fans and radiator are OK. The guage reads the same from about 135 degrees to over 200. I used a scanner to watch what was going on, because the factory guage is basically OK, Whoa, and $$$. I was running a 180, and at idle the temp still came up to 200 or a little more. I swapped back to the 195 to see if mpg improved. Pix is with 195 after 15 minutes. Included some pix of water pump internals also, old and wobbly on the left.

At idle, the fan can't move as much air as when rolling down the road. I would like to try the "Saudi Grille" conversion listed in this forum, I'm on the hunt for a donor grille. I suspect the Saudi style grille will improve things at idle.

Here's to hoping it is an airflow issue, and may we save head gaskets for another day.

 

First check your belt routing.
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If that is good then it sounds like your water pump is bad.
If you continue to overheat the engine you WILL blow it up, it is a all aluminum engine and they do NOT like to overheat.

 

I'm with spike check belt/ bad water pump fits.

 

Yep, that was my story as well, PO had belt routed wrong, bad fan clutch, electric fans reverse wired, radiator full of calcium, water pump started leaking, and I thought it was OK because the guage was not going out of range at the top of the scale.... sorry I forgot to add the belt route.

 

I would be pricing used engines and deciding if the 94 was worth the investment to correct.

What is the overall condition other than the engine?

 

Sold Mutley one because he started the overheating deal I fixed it by doing what we did to the race car.
1. Reverse flushed the radiator
2. Checked ALL hoses fro being tight
3. Took the plug off the radiator on top and then filled the system to get out any air.
4. Added Quick Cool and Stop Leak like you have to with the old Jag cars.
This cured him to being able to run in 100+ deg with the A/C on.
But once a vehicle leaves me stranded it is GONE.
The wrong route of the belt is and easy But I will put my money on the impeller in the water pump being bad OR corroded to a smaller size and not moving the water. Also PUT THE TSAT BACK.
My $.02

 

I will put the thermostat back. An old school mechanic once told me that in the deep heat of summer the tstat is going to open at 100% anyway and a;llow continuous max coolant flow. She over heated with and without the tstat... so that is not it . I will put it back eventually.

Will look for the chem test to see if there is a head gasket failure with combustion gas entering the coolant. That would make sense since we see and hear LOTS of gas or boiling. Will try to video this too and post it. Will test all this this prior to replacing the water pump wich was new 3 years ago.

Will post updates. The general conditoin of the truck is outstanding considering it is almost 17 nyears old! The engine HUMS a sweet song. People can not belive it is the orig engine. Sound smooth and sweet... way better than some 5-9 year old cars.

Joe

 

Old skool was thinking about Detroit iron when people had "winter" and "summer" thermostats, etc. And he did not have a scanner to read live data. These engines hum along at operating temperature, with the stat opening and closing, keeping the water at a stable temperature. Even at 100 degrees outside. Once you slow down (or reduce air flow or water flow, or both with belt routing) things change and stat may stay open for maximum cooling and even that may not be enough, so temp rises slightly under normal conditions.

What does coolant temp guage read "normally" in your truck at highway speed after initial warmup? (8 o'clock, 9 o'clock, etc.) If you are "normally" running at the 9 o'clock position, IMHO you are already too hot, from something(s) that is marginal.

Please verify belt route, fans blowing right direction, etc., and all the other free things. Water pump is easy to do since you already know how to take fan clutch off. I did mine after it started leaking around the shaft and the pulley was wobbling, got a clean one from a low miles wrecked D2 for $6, same pump on both versions of Disco. Has several different sized bolts.