2001 Isuzu trooper, antifreeze leak, not water pump?

My son-in-law’s 2001 Isuzu Trooper, 102,000 miles, developed an antifreeze leak as shown by antifreeze coming out below the timing belt area.

The OEM water pump only had 28,000 miles, but he assumed it was bad. He did look all around the motor, trying to find a bad hose or something that might explain it. He looked for the alleged freeze plugs, but nothing near the area at all.

Finding nothing, he tore it down, and put in a new water pump, lifetime from Autozone, also new timing belt while he was at it. He is very careful, uses torque wrench, gasket shellac, anti-sieze, etc.

When he got it back together it started instantly. So did the leak. Again, he looked all around but it still shows nothing that might explain it.

I agree with him that the odds of a new pump also being bad are slim. He drained the antifreeze, and will try again tomorrow after school. (He is a teacher.)

I suggested he open it up, and put the hoses back on, add liquid, and look at it that way, uncovered, to try to see where it might come out.

Are there any bolt holes penetrating the water area plugged only by bolts or some other thing to look for? We are really puzzled.

Thanks for any tips.

I forgot to make it clear he looked above the water pump area/covers, and saw nothing. Best as we can tell it has to be coming out of the covers.

Got it all apart again. It looks like a gasket leak around the thingamabob that the upper radiator hose connects to. Not sure if it’s called water manifold or water outlet pipe. We assume antifreeze was leaking out slowly, and running down by the timing belt and out. So far he has not found instructions on gasket replacement, so he will probably have to play it by ear.

To make it worse there are no Isuzu dealers down here in McAllen any more, or so he said. So, he may be ordering online if Advanced/Autozone don’t handle the gaskets. I see carpartswholesale stocks such things.

He is glad to find it and can assume he can fix it. With a young son and a Odyssey to pay for, he wasn’t ready now to buy a new car. He needs to get by two more years.

When we got the water manifold apart, the two gaskets looked good. However, the o-ring for the heater inlet, aka as pressure gasket, was badly deteriorated. Cost – 95 cents, overnight shipping $40 or $50. I am going to post details here, because it is likely others will have the same problem. When a gasket gives up the ghost with normal extended use, it is likely it is deteriorating on other vehicles as well.

Wait a darned minute. I did find a page with that exact leak, and a jpg picture showing water all over under the intake manifold. It referred to a bad o-ring, but did not define it. Of course, that was the same one and I did not understand it till now. Mental note to self: if anyone asks about an Isuzu leak, clue them in on this exact issue. (Re-googling now that we know the problem, it is apparent this is a common problem on Isuzu.)

Apologies for commercial link, but we found no other good layout for parts in this area, and his Isuzu manual showed nothing at all. Hope the link works if anyone else has Isuzu leaks.


He did not buy it from this company, at least I don’t think so.

Water manifold is #20 in this drawing. Water manifold gasket, #21 actually is needed X2, though not shown but once. It is also known by some vendors as outlet gasket.

And, #29 is the o-ring. We believe it was the culprit. Of course, he is also replacing #21 X2.

This is another example of advice by our gurus, that it is important to get a good diagnosis before starting to replace parts. My son-in-law is a brilliant man, but he (and I also, blush) lacks experience to clue him to the possibility that a sneak leak above could appear as a water pump leak. Yet, even with his work, his bid from a local mechanic just to replace the water pump was $1200. So, the wasted parts he bought, and the rental car, which he would have had to rent in any case, are still nothing in comparison.

And, most likely, the mechanic would also have missed the real cause. No way to tell, but that is my opinion, so the costs would have resulted in a car that still leaked.

He was distraught enough when the water pump didn’t fix it that he started shopping for another car, and with a new baby, and the Odyssey to pay off this was not a real good time to take on another car payment. When we put the hoses back on and filled it with water, and he saw that leak, he at first thought it was a major task, and looked again for cars on the Internet. When I found this breakdown, and he realized it was an easy fix, he really beamed. I am glad he is the father of my adorable grandson. He is a good man.

The mistake was jumping on the common water pump leak without verifying it. He realizes now he should have uncovered the water pump, then put the hoses back on and added water to verify this with the covers on before working on the water pump. This was a case of lacking experience. He will never make that mistake again.

He is a very careful worker. He uses anti-seize and new hardware whenever he can, and every bolt is torqued with a good torque wrench. When he has that car timing belt et al reassembled, it starts almost instantly and runs perfectly.

Thank you for posting this and the diagram.
I think I am having the same problem with an '89 Trooper.
I have the leak which does not appear to be coming from the pump.
It began recently when I ran the heater for an extended period.
Does the manifold have to be removed to replace the o-ring?
It look like just the hose need to come off. Just wondering.
Checking into this later. Thanks for the info.
Mike (please reply by email if you wish, mjguillory@ar15.com)

No, the manifold did not need to come off. The parts as shown in the link above are right there, but I am not sure the 1989 will be the same. I have no idea of that.

Sorry I can’t give you more help. If we were standing in front of the car, I could point, but it’s hard by typed word. Look at the link and the car until you see if it’s the same.

One photo of a 2001 era car showed antifreeze on top of the motor, a big leak. On my SIL’s car it only drippped down on the floor.

I think i have the same problem i just changed the water pump on my 1998 trooper which has the same engine as yours.It is leaking again and it is coming down from under the timing belt cover.I can’t believe it would be the water pump so i went out and tried to stick my finger under the water manifold housing and i could feel ailttle antifreeze.Can you tell me where you got the parts i noticed in the link that this site does not have number 29 oring.Also did you replace the thermostat gasket also.Kevin

By e-mail, Migillory says:

“I noticed I have antifreeze on top of my radiator, on
the plastic cover that spans between the front of the
radiator and the grille. I’m not sure how it is getting
up there. I think the leak only occurs when I run
the heater and the trooper is not overheating so I’m
not “too” concerned right now.”

I don’t know any way to get coolant there except from the cap if it is close, or a bad radiator. Any ideas?

I still don’t know what my problem is. I haven’t had time to look hard.
The water on top of the radiator was coming from the radiator cap though.
I checked and the radiator was almost empty. I don’t know why it didn’t
occur to me to look before, but it was overheating and pressure was blowing
water out the cap. I let it run and it took a lot to fill it back up. Some water
bubbled up out of the radiator a couple times leading me to believe the problem
was head-gasket-related. However, once I got it properly filled the bubbling out
stopped and hasn’t happened again. I have driven a few hundred miles since
then with no leakage or overheating. I really don’t know what the problem is. ~mjg

Note this was November, 2008. Two weeks ago, my SIL noticed an antifreeze smell. He couldn’t find the leak this time, so he took it to a mechanic, who concluded it was perhaps freeze plugs somewhere around the transmission. So, I think he said they pulled the transmission, and discovered there were no freeze plugs.

With more searching, they learned there is ANOTHER O-RING, this one under the exhaust manifold. I will quote his e-mail in a minute. They also discovered one of the new o-rings he put on in November is bad already. I think they found o-rings in Brownsville, and my SIL had to take off work and drive down to get them.

Quote from his e-mail:

Let the readers know that there is another o ring o a water pipe the is connected
to the back of the thermostat area. this is a larger o ring than the one the is
connected to the water manifold. it is located under neath the intake manifold.
to get to it you must remove the intake manifold, gas rails to the fuel injectors, and the egr valve. this is a big job and will take much time.

Also the leak will show as if the truck has a leak between the transmission and the engine. There are no freeze plugs between the engine and the transmission on the 2001 trooper, so they will not have to remove the transmission. the reason it show as if you have a leak from there is the on the top of the engine block there are 3 raised sections or compartments.

One compartment where the thermostat is located somewhere near the middle of the block. the other one is near the rear or next to the fire wall. these compartments have a hole drilled at the bottom of the compartment so the if any water gets in them it will drain.

Hope this helps

End quote.

Personally, I will not recommend anyone buy a used Isuzu because of this outrageous design flaw, for what it’s worth.