coolant system frustration

I know this topic has been mentioned many times, but I just can't figure it out.

1. The cooling system was working fine, with a small amount of leakage requiring weekly top off.

2. Valve cover gasket leaking so bad that the truck looked like a mosquito sprayer. Changed VC gasket and put new o-ring in the t-pipe.

3. Apparently system was holding pressure as three coolant hoses blew. Replaced all of them.

4. Engine will now run for only a short time before creeping up to the red. sometimes it will come right back into range. other times it will stay in red. other times it will bounce back and forth.

5. Warm air at best coming out of heater. After running a little while nothing but cold air.

6. Tried all the air in the system tricks. heater hose purge, truck on incline, etc. Still overheats

7. Water pump is less than two years old and has about 20K on it. see no leakage.

8. Fan clutch appears to work. turns with little resistance when engine cold. spins with resistance when hot. no movement or noise.

9. Radiator was replaced about the same time as water pump. After running for a while the lower portion is hot, but not as hot as the top.

10. thermostat was replaced at the same time as wp and radiator. Not oem (am getting one) but it seemed to work before.

Obviously I've missed something. I don't have a lot of money to just go replacing things that appear to work. But I need to do something.

Sounds like its still air locked. Not sure what to do when the usuall tricks dont work. Power flush maybe? Maybe some crap dropped into the system with all the work at some point and plugged something up keeping it from circulating right.

I don't speak from personal experience but there have been many comments on the importance of using OEM thermostats. I would suspect this first.

'99

I bet you it's the thermostat, most NON-oem's don't keep these engines within proper spec.

Hopefully no long term damage was done, these engines are all aluminum and don't deal well with overheat conditions.....neither did my late toyota

Still no joy. I went through the air is system thing many times. Didn't help. Replaced the thermostat with oem. didn't help. replaced the radiator (though it was hot on top, cold on bottom, so were the hoses). didn't help.

One other possible clue. As it warms up the heater will blow warm air (not hot) but when the engine runs hot it's nothing but cold air from the heater, even when the engine temp comes back in range.

Gizmo, you mentioned power flush. what is that?

Just my 2 cents worth here-

If your radiator is hot on the top and cold at the bottom you are not getting circulation in the cooling system. It should be hot on the top and warm at the bottom.

If your heater blows warm air then turns cold, you are not getting circulation in the cooling system.

You should be able to remove the cap, warm up the vehicle to normal range and see the fluid move from right to left in the radiator. If not, you are not getting circulation in the cooling system.

Did you install the new thermostat in the proper direction?

Did you install a brand new radiator? If not, I would remove the cap (when cold) then the bottom hose. The fluid should gush out very, very quickly.

This is straight from the Isuzu shop manual-

*Do not let the engine overheat*

1). Remove the cap and fill the radiator to the base of the filler neck with 50 / 50% coolant solution. Fill the reserve tank to "Max" line.

2). Block the wheels, Shift to "Park" and warm up engine at 2500 - 3000 RPM for about 30 minutes.

3). When air comes out from the filler neck and the coolant level has gone down, replenish with 50 / 50% mixture. Repeat until the level does not go down. Stop engine and install radiator cap. Let the engine cool down.

4). After engine has cooled, fill reserve tank to "Max" line.

5). Start the engine. Run engine at 3000 RPMs and make sure there is no rushing water sound from the heater core. The heater core is located behind the center console.

6). If rushing water sound is heard, repeat this procedure starting at step #2.

If the thermostat is OEM / new / installed correctly, the radiator flows smoothly and there is no air lock, I would suspect the water pump even though it is fairly new. The pump's impeller is usually a press fit onto the shaft, perhaps this has worked loose.


Good Luck,
Dale

dale;
I do believe it's the water pump (the lack of circulation thing checks out, and I heard a ugly noise after the big repair. So, if I change out the pump, do I need to do the timing belt even though it was done two years ago?

If you decide to replace the water pump, inspect the timing belt while you are in there.

Make sure the belt has no oil or water on it and the teeth are in good condition.

It should be fine as it was replaced two years ago.

Be sure the other things have been checked as a water pump R & R on the Rodeo will be a lot of work.


Good Luck,
Dale

If you removed T stat make sure its not in backwards. I did some work on a Dodge Durango and did not pay attention to how I put it in(since it was at the bottom of the engine). I fought for a whole day trying to trace down a overheating issue. I was about to get another T stat when I seen where it was in backwards, problem was then corrected.

Is the Rodeo still overheating?

I finally found and repaired the problem. It turns out the water pump was working good, but a timing belt idler had come apart. I replaced it, and checked the water pump while I was there, and it seems to be working well now.

Good to hear that you were able to solve the problem.

well, I was a little premature on thinking the coolant system was fixed.

Still having overheating issues.

I took the thermostat out and poured coolant into the radiator. It quickly came out of the thermostat housing. I put the housing back together without the thermostat in. I could see coolant moving right to left in the radiator neck. So I assume the system is not blocked and water pump is moving coolant. If I put the thermostat in the truck will overheat within a few minutes.

truck will run for a while and appear to be doing ok and eventually heat up. When it does heat up I've noticed the overflow tank will be full and even blowing coolant out of the top. However, when the truck cools down the coolant doesn't seem to be going back into the radiator.

I have driven for over an hour on the highway and the temp stays at the low end of normal operating range.

after cooling down I will have to add maybe a pint or so of coolant.

I took the air plenum and fuel injection rail off to check for leak. Apparently I did fix the leak on the coolant tubes. very little coolant on the top of the block. What little there is appears to be coming from a small leak at the head/block area. There was less than a tablespoon of coolant sitting there.

When the truck is running at a good tempature range there is still very little heat from the heater. When it starts to go hot there is cold air coming from the heater.

Is it time to try a new radiator? (I had put a used one in that seemed in good shape)

What about the coolant not being sucked back into the radiator?

Dude, you started this thread by stating in your first post that you replaced the radiator. I think everyone here ASSUMED it was a NEW radiator... I know I did. Now you say it was a used unit. No offense man, but you need to do a better job of honestly and accurately describing what you've done so you don't send people off on wild goose chases.

REPLACE YOUR RADIATOR WITH A BRAND NEW UNIT, PREFERABLY AN OEM UNIT. THEN COME BACK HERE AND TELL US WHAT HAPPENED.

We want to help you, but ya gotta stop making us crazy.

One thing I've learned on aluminum engines, is to never use *used* parts when replacing cooling system items....that engine overheats just a tad too much, or too often, and it's a gonner.

Get yourself a NEW radiator, a new OEM Isuzu thermostat (if you haven't already) and go from there.

OEM Radiator doesn't really matter, I'm running an aftermarket radiator with no problems, but be SURE to definitely use an OEM thermostat!

Not sure if your truck is an auto or 5-spd, but if it's an automatic, remember every time that engine overheats/gets hot, so does the tranny, which will drastically shorten the life of both. Make sure to change your tranny fluid as well...and soon.

I know these trucks can be a bugger sometimes.

Keep us posted.

Ramblin, thank you for your useful imformative post. I will do as you suggest.

Horseman, you can kiss my a**, you smart a** little pri**!

the old saying certainly applies to you. So just stay the hell out of my threads.

Ramblin, thank you for your useful imformative post. I will do as you suggest.

Horseman, you can kiss my a**, you smart a** little pri**!

the old saying certainly applies to you. So just stay the hell out of my threads.
Good luck with your repair. You're gonna need it. You're already pushing 3 months with this problem. Btw, I've had a 20% failure rate with new, out-of-the-box radiator knock-offs. You may wish to keep this in mind if you choose not to buy an OEM replacement.

My Modine rad from NAPA has been good for three years or so...

Have an aftermarket radiator too...it actually keeps the engine a tad cooler then the original one did.