Overheating

[tmr416]

I went on a big road trip this summer from Seattle WA to Montana, Wyoming, Utah, and Colorado. My '99 4.0L had never had overheating problems until one day after playing in the mud in Jackson WY. I came down out of the hills and noticed at slow speeds my fan was louder than normal. Then, later that evening when I was climbing back up the trail to find a camping spot, my engine almost overheated. At first, I thought it might be that my engine and/or radiator was coated in mud and having a hard time letting heat escape. I washed the engine/engine bay/radiator as best as I could (while being careful not to soak my ignition coil/battery/air intake). This didn't help. I kept on having cooling issues the rest of my trip.

At highway speeds I was fine. I'd get hot climbing hills, sitting in traffic at red lights, moving slow through cities, etc.

For more context, I put 33x10.5R15 tires on my rig before the trip with Pro Comp steelies. I did not re-gear my axles and have factory 3.73 gears. Could bigger wheel/tire without re-gearing could be more labor on the engine? It could be a bad fan clutch?

I've had issues with my 4.0L in the past with "soft misfires" and a check engine light that coded for a new ignition coil/plugs/wires and had that done almost a year ago. Since then, I've experienced the "soft misfires" again once or twice. Usually, the engine runs smooth and I don't feel any reductions in power. I want to do a compression test to see if I'm losing compression in any of my cylinders. Basically, my biggest fear is that my head is cracked which I understand is common in the high mileage 4.0's. I have 217.5K on my engine.

Any advice on troubleshooting would be appreciated. I haven't had as much time to get out in the garage and troubleshoot since getting back from my trip but am going to start with a coolant flush and thermostat replacement.

 

[Roert42]

I would say that if you are overheating while sitting in traffic you have either, not enough air flow ( clogged radiator or fan problem ) Or not enough coolant flow ( water pump issue, thermostat issue, or a clog somewhere internally )

When the engine gets hot, is the fan spinning? Do you feel the fan drawing air through the radiator?

If you want to replace the thermostat as a troubleshooting method, be careful. I've had three aftermarket thermostats not work properly out of the box, installing parts that may or may not work is not a good troubleshooting method. Go Motorcraft.

OR just pull out the thermostat and test it before replacing it.

 

[Shran]

Couple things... does it get hot with the AC on? off? I suspect you have mud built up in the AC condenser, radiator, both, or in between the two. Might be worth pulling your radiator out and really washing everything and making sure the fins on both aren't bent over to the point where air can't flow through.

I am having misfire issues with one of my 4.0s as well. I think it's actually "carbon knock".... if you google 4.0 OHV pinging you will see what I'm talking about. Caused by carbon buildup and apparently there's even a TSB to fix it with Seafoam or similar product. It's bad enough that it will set off my check engine light under a heavy load. Maybe that's what's going on with yours too.

 

[tmr416]

I would say that if you are overheating while sitting in traffic you have either, not enough air flow ( clogged radiator or fan problem ) Or not enough coolant flow ( water pump issue, thermostat issue, or a clog somewhere internally )

When the engine gets hot, is the fan spinning? Do you feel the fan drawing air through the radiator?

If you want to replace the thermostat as a troubleshooting method, be careful. I've had three aftermarket thermostats not work properly out of the box, installing parts that may or may not work is not a good troubleshooting method. Go Motorcraft.

OR just pull out the thermostat and test it before replacing it.

Thanks for the advice about parts. Just called my local Oreilly's to see if they had thermostats and I'll check to make sure it's Motorcraft. I'll have to double check while troubleshooting to answer the questions you asked about if the fan is spinning or not.

 

[tmr416]

Couple things... does it get hot with the AC on? off? I suspect you have mud built up in the AC condenser, radiator, both, or in between the two. Might be worth pulling your radiator out and really washing everything and making sure the fins on both aren't bent over to the point where air can't flow through.

I am having misfire issues with one of my 4.0s as well. I think it's actually "carbon knock".... if you google 4.0 OHV pinging you will see what I'm talking about. Caused by carbon buildup and apparently there's even a TSB to fix it with Seafoam or similar product. It's bad enough that it will set off my check engine light under a heavy load. Maybe that's what's going on with yours too.

It gets hot with the AC on. For most of my trip, unless I was cruising the highway, I would go oldschool and roll the windows down and keep the air system off AC and let it blow warmer to help displace hot air. I think it'll be worth it for me to do what you suggest and pull everything out and wash it thoroughly. I got lots of mud in the engine bay

I've heard about the Seafoam treatment before. Might be worth me looking into and giving it a try. Thanks, I appreciate the advice.

 

[Shran]

My 92 Explorer gets hot with the AC on and only when the AC is on and only when I'm moving slow or idling. I think a combination of half the condenser fins folded over and a custom front bumper, winch, and lights blocking part of the grille does not help. There is also a baffle that goes around and in front of the condenser that is missing on mine. Make sure that's present on yours, it helps direct air through... there also should be two foam "seals" on the sides between the radiator and condenser that also help direct air through both. But it's amazing how much dirt and leaves and crap get caught in there.