seasoned_geek

I've only had this Jeep for a couple of months. Yes, I had my local mechanic pull the dash out replacing heater core and A/C unit as well as the blend doors. Gotta love the bean counter who went with that foam supplier. Even wrote a blog post about the repair.

4.7 High Output V8

Has a mysterious coolant loss though. I think it had the coolant loss problem before I bought it as coolant low warning came on when first started. I don't "smell" antifreeze nor do I see it dripping anywhere. Various searches turn up mention of an infamous "coolant loss while A/C running" but I cannot find any details on it. Kind of like an urban legend we are all supposed to know. Does someone have a link to the exact details behind that?

Oil is clean.

No smoke or funny smelling exhaust.

No sweet smell in cabin nor does the carpet seem wet on passenger side. I mean the heater core is new so unless it was junk from the factory...

At first I was willing to write the coolant loss off to air trapped in the new heater core. I'm almost done adding my second jug though. The core cannot hold that much.

No heat problems. Gauge never goes above 210, most times doesn't even reach there.

Weather is hot now so been running with A/C set to auto and 70 degrees whenever I drive it. Since I don't see anything on the ground when letting it idle I'm interested in finding out more about this "coolant loss with A/C running" issue.

XJRed96

Try renting a coolant system pressure tester from your local auto parts store and going from there. If there isn't any visual leaks or the system holds pressure, I would begin to suspect a bad head gasket and/or intake manifold gasket.

dave1123

Welcome to CF!

If you're only loosing about a quart a week, I think I know the answer to that. Instead of the normal "weep" hole on the water pump bearing like the older ones have, the newer ones have a "weep chamber", a small pocket that holds about a tablespoon of coolant leakage that's allowed to evaporate instead of run down the front of the engine. This was designed to protect the serpentine belt from getting contaminated and flying off. When the leak gets large enough, in drips into the back of the pulley and is thrown off on startup. I found this out with my 4.0 when I started it up on the lift to bleed the brakes. As soon as the engine started, there was a torrent of coolant that spilled down the front of the engine, then stopped! Looking at a catalog for a replacement pump, the AC Delco ad mentioned this chamber. WTF? What crazy engineer designed this? Anyhow, changed water pump, end of mysterious coolant loss. I hope this helps.

seasoned_geek

Thanks for responses. It's a 4.7 HO not a 4.0 so should have completely different water pump. I know the 4.0 I had in the 90 Wagoneer Ltd. was unique. Water pumps for it only fit a few years and newer ones spun a different direction.

While it was hot I stuffed a piece of card board under the engine area. As of last night no drips of any kind. Same thing just now. Later today I may take it somewhere so will see if anything splashes onto the cardboard after starting. The serpentine belt looks okay but is starting to sound like it either needs conditioner or replacement. Could be unrelated though.

Surfing around yesterday did turn up this link where a Jeep mechanic of several decades says the 4.7 HO has a unique problem. I'll quote it here in case of link rot.

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Hi,the front timing covers on those blow the gaskets on the water passages,rarely seen head gaskets because they are a multi layered steel gasket.Intake do not have any coolant through them.To replace the timing gasket figure about 2.5-3 hrs of labor + parts

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dave1123

Okay, I just threw that out there as a possible problem because of it's design. I personally have never even been in the presence of a 4.7 so I couldn't tell you much about one.

XJRed96

do you have any wetness inside the cabin? does it smell like coolant with the heat on? short of the engine gaskets I mentioned earlier the heater *Core* is the only other part that would leak and leave no evidence under the engine. I would still recommend pressure testing the system.

seasoned_geek

No worries. I really don't know what happened to the 4.0. The original ones were rock solid. Change the oil regular and you could easily get 300K out of one, especially when paired with an AW4. Something changed after the 1990 model year. Before that the same oil filter worked for both the 4.0 and the AMC 360. Some time in the 1991 model year the engine changed. Takes a different oil filter and many other different parts. Now I see all of these stories about cracked heads long before 200K along with other anomalies.

The 4.7 HO (not to be confused with a regular 4.7) is a sweet engine. Yes, it gets near zero mileage. I think the best I've done is 18. Yes it will burn base gas but premium is recommended.

dave1123

I think you're a little off. The major change was for the 99 models with the 0331 head, relocated oil filter and motor mounting bosses, and the addition of the coil pack. With the exception of the new cylinder head, the original AMC engine continued until 2004 with only those changes (motor mounts and oil filter).

seasoned_geek

No wetness in cabin. The entire HVAC system, sans the A/C compressor was just replaced. Thanks for the feedback though.

seasoned_geek

Major or not I know my 1990 Jeep Grand Wagoneer with AMC 360 and 1990 Jeep Wagoneer Ltd. both took the same filter so I bought a flat of them on-line. A year or two after getting both of those Jeeps I had a chance to purchase an Uber-sweet 91 xj with the supposedly same 4.0. Thankfully I went on-line to a few auto parts places and looked up the filter. It was different.

When I purchased a shiny new long block for the little guy from PowerPro2000.com (back when they existed) the guy on the phone told me they had one in stock local for a 91 but had to ship one for my 90 "from the warehouse" which was actually Performance Products, at the time the Mopar factory reman center.

It is possible both things lied to me but...I was buying the engine no matter what. The dude had nothing to gain by saying the "local inventory" one wasn't right. Instead of a 4+- hour delivery time the engine arrived at 4 p.m. the next day. My mechanic had to finish the engine replacement they had going on before they could start mine so even 3-days shipping wouldn't have mattered.

Back in the day when the 4.0 came out it was considered the most solid engine ever made this side of the AMC 360. Way before the Internet I knew/met hundreds of people who had them and you never hear of them failing with less than 300K on them if the owner kept the oil changed. Now, when I search on-line for this coolant loss issue I stumble into tons of videos and articles about "notorious head crack" and other anomalies that all seem to be for 4.0 motors built after 2000.

seasoned_geek

Oh. I drove the Jeep to town yesterday and parked on the cardboard in the shed when I got back. Saw nothing dripping. This morning there was a large wet spot on the cardboard under where the coolant tank is in the passenger rear. Yes, the coolant was once again low. Not low enough to trigger an alarm, but much lower than it was the day before.

True the air conditioner drains back there as well, but I parked the Jeep around 5pm last night and didn't look until after 8am this morning. Water from the A/C _should_ have had time to dry.

Removed the radiator cap. Radiator clear full, but the cork under the cap looks bad. In all my surfing I did find a post about this model engine having an odd radiator cap failure. The oddity is that the failure only manifests when engine gets to 2000 RPM. Lets too much coolant out into reserve container causing it to overflow when ramping up to highway speed.

My next "fix" attempt will be to replace the radiator cap.

I have also stumbled on to many reports of reserve tanks cracking but seems odd a plastic tank could crack in such a way it would only leak when hot.

Yes, a pressure test once I try a new radiator cap is a good idea. It "could" be leaking into a cylinder which would explain why I never see any on the ground. The thing runs so good though an it is getting around 18 MPG like it should.

Thanks for everyone's ideas and suggestions. Will keep you posted. If it is going into a cylinder will drive it until it fails. I'm a firm believer in the motto "don't pull a head, swap the engine."

dave1123

Okay here's the skinny on the 0331 head, just for your edification. Also explains why a 90 and your 91 are different.

From 87-90 they had the 2686 head on them
From 91-95 they had the 7120 head on them
from 96-99 they had the 0630 head on them
And after that, they had the redesigned 0331 head. Most of the differences on ALL these heads is in the valve ports. The 0331 valve passages were enlarged for better airflow that resulted on weak spots in the casting. This was fixed in 02 by casting the head in a different material. These are known as the "TUPY" head. Chrysler never admitted they had a problem with the 0331 head, but somehow they remedied the problem.

The basic engine lower half has remained unchanged until 99.

seasoned_geek

Thanks!

seasoned_geek

Well,

Last night I dropped the Jeep off at my local mechanic. Just got off the phone with him. Pressure testing found a pin-hole leak on the driver's side of the radiator. Only leaked under high pressure. Getting new radiator. Will let you all know if that was the only point of coolant loss.

As many Jeeps and other vehicles as I have owned over the years I have never seen a radiator leak from the front only under high pressure. First for everything I guess.

Batman229

Question about the heads...

I have a 2002 Grand cherokee laredo. Mines had the same coolant loss with no appearent leaks. Mechanic said replace radiator cap. Did that now still same thing. Did they roll over using the 0331 heads in the 2002's to get rid of them? Or is there a certain date of manufacturer they stopped using them?