Shifting AW4 into reverse while going forward

Family member in a near accident, panic stop freeway, shifted from drive to neutral and thinks it may have gone into reverse (it was dark and the shifter lighting does not work). AW4 Renix 4x4. The engine died when she moved the shifter during the panic stop (reverse???).

What damage might that have done?

How would would check? I am 1000 miles away, so I was asked...feedback

Ecomike said:

Family member in a near accident, panic stop freeway, shifted from drive to neutral and thinks it may have gone into reverse (it was dark and the shifter lighting does not work). AW4 Renix 4x4. The engine died when she moved the shifter during the panic stop (reverse???).

What damage might that have done?

How would would check? I am 1000 miles away, so I was asked...feedback

Click to expand...

Was the shift to neutral or possibly reverse intentional?



The AW4 doesn't have any synchros or gears that physically disengage or engage as it shifts. It's all clutches, brakes, and a couple of one-way clutches. If it's still working in all gears and not making funny noises, I don't think I'd worry too much about it.

Albeit not good for it, I dont see it really causing any serious damage to the trans unless the engine was at WOT or something like that.

So far, it has not manifested any AW4 issues. Fingers crossed.

Maybe you got lucky, my youngest daughter did that doing around 50 MPH, 6 weeks later the tranny grenaded. A half handful of broken bits and pieces laying in the pan.

Ugh, :-( Right now the rig has overheated for the 3rd time in weeks, and just spent 6 hours fiddling with trying to solve a power steering leak...flushing it... 1200 miles away, a day ago. Among other things...

Leaning towards a sticking T-stat...

I wouldn't worry about it unless it starts slipping or explodes either. I looped my 98 XJ in a snowstorm (long story short, snow was coming down hard, highway unplowed, had to get home, rear left tire had been victim to a rock a week earlier leaving me with 3 26" studded snows and 1 29" half bald spare tire, had to run it in 4wd to get any traction... it was VERY squirrely) and caught traction while sliding backwards. All it did was stall the motor, I put another 30k miles on it after that.

I have seen a nearly dead AW4 cause severe sporadic overheating at highway speed (it was slipping and dumping a ton of heat into the fluid) but I would suspect other sources for an overheating problem. AW4s are pretty tough. Hell, Team Petty Cash slammed theirs in reverse by accident on the track and all that happened was they slid off course, stalled the motor, and busted the leaf center pin. Trans was fine.

http://www.fourwheeler.com/events/1705-a-road-racing-jeep/ (search for "accidental")

Wowzers. The overheating was first idling in park a year ago, new clutch fixed it, then about 5 weeks ago making deliveries and long idles in park, etc..... it overheated again. The E-fan works, but I do not think the Temp switch is working. Clutch is a year old (from the last time it overheated in park sitting).

Over heated again sitting in park too long again about 6 weeks ago. Then fine for several weeks (but not allowed to sit and idle in park except at stops), and good for many 60 mile drives.

Is there a freeze plug on the rear of the block? Does the tranny need to be backed off to get to it?

Waiting for more inspection, and running data right now....

there is one on the back of the block inside the bellhousing as well as one on the back of the head.

Both are proper bastards to get at... found a pic but haven't bothered to upload it so I can embed it here.

OK, she just ran a test. Started out with temps around 39 F. Upper radiator hose and T-stat housing hit about 100F at the same time, making me thing the T-stat may be stuck open (some or all, no idea which).
T-stat housing was under 180 F, maybe even 160 F max when coolant started blowing out the bottle (cap was off to try and add coolant). Ambient (Colorado Springs was about 39 F ish?)

I am thinking the block has air in it. Hope its not a head gasket leak.

She thinks (not verified) that the bottom hose/nipple on the coolant bottle may be leaking now, but that is not the main issue!!!!

Plan to pull the upper rad hose at the T-stat this weekend. Then fill the block and radiator from the coolant bottle and vent air through the radiator and upper Rad hose. And then rerun the test to see what happens.

Hoping the air already in the block is the only real problem. Tranny fluid and oil are normal.

You may have already checked, there may be a flow issue. When it gets up to temperature, squeeze the top hose. If it is rock hard you likely have a flow issue. When everything is working well that top hose should collapse with two fingers and a thumb, if it isn't really stiff with age.

Flow restriction is often the radiator, sometimes a hose separates internally.

What I am hearing is with the coolant cap off, just as soon as the T-stat seems to start to open it blows massive steam/coolant mix out the coolant bottle.

This is not a radiator issue.

I also do not think it is a head gasket issue.

But on Renix, the radiator is a trapped loop with no air exit.

I think the bottom of the coolant bottle feeds the water pump inlet (3/4-5/8 hose) and the second hose by passes the T-Stat (driver's side) and lets hot coolant from the head(?) under pressure from the pump pushing coolant to the radiator then to engine block feed/flow, and then through the head, and then to the heater valve Y that splits flow/diverts flow to the bottle or heater core?

So why does it suddenly blow steam out just as the T-Stat gets in the 180 to 190 F range and starts to open?

I am trying to plot the path of the steam eruption through one of the 2 hoses to the coolant bottle to make sense of how it can do that.

Keep in mind I am getting second descriptions from 1200 miles away. I was on the phone step by step, but my data is not perfect with out being there.

The coolant hose going to the heater valve/coolant tank and the return have a secondary function. It allows coolant to bypass thermostat so the hotter coolant get to the thermostat. That loop helps make the thermostat much more responsive.



Way back in my racing days we'd plug that bypass and had heating issues, the motor seemed to run either too hot or too cold in cycles. We learned to make a loop instead of plugs to bypass the heater. It was most prevalent in the first start up cycle on a cold motor. Just a thought, but I've seen some really gunked up heater valves.

Another thought, if you've replaced the thermostat you can't use the supplied (universal) gasket. The Jeep gasket is the only one that will work, it has a cut out for that bypass.

Just had an idea. It may be that the engine block needs to get to a critical temp, say 190 F +/- for the trapped air and or ( and or trapped coolant from a stuck T-Stat?) to boil and steam up (pressure) thus blowing coolant and steam out of the heater hose on the side of the coolant bottle into the bottle and out the bottle hole top side.

Also now wondering if the bottom coolant bottle hose ( it may not be sealing, not sure yet...., but it was starting to look like it might not be sealing there in the last minutes of the tests) may be letting air into the coolant pump that then pumps air bubbles into the block.

Or the bottle emptied when the T-Stat opened, and drained and pushed air into the block in seconds, that led a blow out seconds later?

I have never ever in 45 years seen what she says it did. So I know it is not any of 101 known coolant issues we all know all too well.

Nothing on the entire cooling system has been changed in 24 months, except the heater 3 way valve about 4+ months ago.

I see no way the heater valve could be involved. It is under pressure feed from the coolant pump outlet.

Only other possible path is for steam to go right through the coolant pump outlet to the inlet and back to the bottom of the coolant bottle. With I find highly improbable.

We know there is/was some air in the engine/radiator because we were able to get the bottle to empty as we filled it 2-3 times before the blow outs.

So my plan is to pull the T-stat-Radiator upper hose at the T-stat and heater hose then fill the block and radiator using the Coolant bottle, which has never failed for me. That lets the radiator de-gas fully and the block and head.

Someone using one of our cherokees when the new belt idler crapped out and they kept driving, even after I begged them to pull over and wait after they first heard a bad noise, long story but she broke just about everything in the front belt area where that idler gave out. By the time I met up with her the belt was destroyed, heater outlet pipe on the water pump had a hole chewed in it and my poor Jeep momentarily hit the high mark on the temp gauge before she turned the engine off. When I got there it would vent steam through the reservoir tank (other time I’ve seen this is BHG on another car) . This was a ho Jeep not a renix, so the cooling system is different.

After I got the Jeep home I replaced just about everything I could up front, lots of things were smashed by that damned pulley. once I was done the old Jeep ran good just like it always has. I do remember it being a pain to get the system fully burped. Not as bad as newer cooling systems, but not as simple as I remember it being, this time the block and heater core were really drained, all kinds of pockets of air.

On mikes Jeep I wonder if the block is blocked and if the cooling system is correct for renix, maybe a previous owner mixed and matched.

I’m sort of surprised there isn’t a reverse lock out, but thinking about it on those transmissions I’m not sure how it would be done.




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One owner dealer maintained city rig was the history, little old lady, and we bought it 2 years ago. All OEM stock.

Only thing replaced was the Bottle cap and fan clutch a year ago. Heater valve about 12 weeks ago. Plus some 50:50 old school coolant.

Brake work, one front axle U-joint. Tires, and gas. And a NAPA top end CPS about 12 months ago and then a new battery a week later.

Been a 120 mile a day DD for 2 years running up some respectable miles. Even in the mountains.

1989. Renix. Paid $1600 for here, 4x4.

It’s getting air from somewhere. Freeze plug seeping? Pin hole leak in a hose?

Maybe they can pressure test the cooling system.

Could the water pump be a issue? Reminds me of when ours overheated because of that pulley cutting heater outlet pipe and there was no circulation because the belt was gone.

Ultimately if everything else is good it could be a head gasket issue. Doesn’t have to have white smoke to burn just enough to overheat the block. We assume it’s just burping air and not CO2. Although the 4.0 are hard to kill with brief temp spikes.




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Only visible leaks, ever, have been coolant/steam blow outs at the coolant bottle cap.

New Volvo 21 psi cap and new Clutch fixed it over a year ago.

Last blow out was while trying to fill the system running with no cap. Blow out was just as the T-stat should have been opening (Housing read and had just reached above 190 F, using new IR tester) after running and adding about quart of coolant during warm up, keeping the bottle half full.