MummifiedCircuitry
Adventurer
Old cap and new cap
Gen2 overheating when driving slow hills
- Thread starter MummifiedCircuitry
- Start date
After my commute home from work, so fully warmed up, with an IR thermometer gun, at idle just a few minutes after getting in the garage, I measured a 45 degree temp drop between the radiator inlet (top) and exit. For what it is worth......what is your truck getting? The heater core hoses were balanced, and were about 10 degrees cooler than the radiator input, blower not on. And my temp gauge has always operated right in the center for as long as I can remember. My normal operating temp is about 200-205F, taken from scan gauge.
Last edited:
MummifiedCircuitry
Adventurer
Do you know what the pressure rating is on the new cap? Radiator caps are designed as pressure/vacuum relief valves but if the spring is too heavy it might not function properly:
I'm assuming you've tried it with the old cap installed?
The new cap is 13psi, same as the old one. I just tried the old cap on the new radiator and took it for a drive, it didn't overheat, but did get a bit hotter than normal temp at the steepest slowest section.
MummifiedCircuitry
Adventurer
Thank you for checking, I don't have a temp reader to check mine though. I'm also running a 170 degree thermostat, which is 10deg lower than OEM I believe. My temp has always sat just below halfway before and after i upgraded the cooling system. After putting the old cap on, I just took it up a dirt road that is 5mph and steep, the temp stayed at the point the whole way except right before the road ended it started going up and got to the halfway point.
MummifiedCircuitry
Adventurer
Unfortunately, I don't have anything to read temp with. I've been eying a scangauge, I might have to pick one up at least for temp alone.
After I put the old radiator cap, it went up just above the halfway mark, but it just started as I reached the end of the road, so I couldn't continue to see how hot it'd get.
toyrunner95
Explorer
I have worked on a bunch of different cooling setups. The cooling system in a vehicle is fairly simple. Lets start with the basics, I am sure you already know that but outside eyes help.
Coolant warms up in the block until the thermostat opens and allows it to circulate through the radiator. In the bottom out the top. (or vise versa depending) the the water temp sensor is in the manifold usually on the cold side of the thermostat. So the gauge reads the temp coming out of the motor not at the radiator.
The fan pulls air across the fins of the radiator thus cooling it. The water pump combined with the expanding fluid creates pressure opening the radiator cap and allowing excess to flow into the bottle. When the system cools it sucks the over flow back in.
Here is my theory. You are not getting enough air movement across the fins. The fans are blocking air flow. HOWEVER, this problem occurred with the stock fan as well. This tells me the same issue.
Lets do a easy driveway bench test. With the truck cold take the cap off the radiator and put a thermometer in it. Start the truck and record the temp and mark the time when you start. When the temp starts to rise with the thermostat opening mark the time as well. Let it idle until it gets up to operating temp and record it.
From there rev the engine at about 2k RPMs with the throttle assembly. In neutral record the time from start to when the fans kick on and the temp. Then see how low the temps get till they turn off. Check these temps against the fan settings and factory settings.
You may have the fans coming on too late and not cooling enough. OR they are pushing the air, flow is important. Furthermore most electric fans don't work with stock radiators. Most upgrade to a thicker radiator dissipating heat faster.
The fact of the matter is the coolant is not cooling. All of this points to something with the radiator. It could be clogged. It might be the water pump not circulating enough coolant as well. Either way you need a baseline.
The water pump..... is this the factory unit? original? replacement? Aftermarket? Do you hear any noises? Belt squeals, bearing screech?
My parents had an older jeep grand Cherokee that had what we called the super fan. when we would tow it bumped up the fan speed by almost triple. It was loud.
Coolant warms up in the block until the thermostat opens and allows it to circulate through the radiator. In the bottom out the top. (or vise versa depending) the the water temp sensor is in the manifold usually on the cold side of the thermostat. So the gauge reads the temp coming out of the motor not at the radiator.
The fan pulls air across the fins of the radiator thus cooling it. The water pump combined with the expanding fluid creates pressure opening the radiator cap and allowing excess to flow into the bottle. When the system cools it sucks the over flow back in.
Here is my theory. You are not getting enough air movement across the fins. The fans are blocking air flow. HOWEVER, this problem occurred with the stock fan as well. This tells me the same issue.
Lets do a easy driveway bench test. With the truck cold take the cap off the radiator and put a thermometer in it. Start the truck and record the temp and mark the time when you start. When the temp starts to rise with the thermostat opening mark the time as well. Let it idle until it gets up to operating temp and record it.
From there rev the engine at about 2k RPMs with the throttle assembly. In neutral record the time from start to when the fans kick on and the temp. Then see how low the temps get till they turn off. Check these temps against the fan settings and factory settings.
You may have the fans coming on too late and not cooling enough. OR they are pushing the air, flow is important. Furthermore most electric fans don't work with stock radiators. Most upgrade to a thicker radiator dissipating heat faster.
The fact of the matter is the coolant is not cooling. All of this points to something with the radiator. It could be clogged. It might be the water pump not circulating enough coolant as well. Either way you need a baseline.
The water pump..... is this the factory unit? original? replacement? Aftermarket? Do you hear any noises? Belt squeals, bearing screech?
My parents had an older jeep grand Cherokee that had what we called the super fan. when we would tow it bumped up the fan speed by almost triple. It was loud.
MummifiedCircuitry
Adventurer
Thank you for taking the time to respond. I really need to get a thermometer to do some testing. This thread is a bit long so I don't expect you to read it all, but the short of it is while sitting stationary the truck never overheats, while driving highway speeds, slow on flat ground, fast on steep hills, etc it won't overheat. I've only had it do it to me on slow 5mph hills, which is a problem because I've been driving them often. My fans aren't wired to a thermostat, they are single speed and wired to toggle switches so they're always on. As far as I know, the water pump is original, the previous owner never mentioned it being replaced. Normally a water pump is quite simple to replace, but on these monteros you basically have to disassemble the whole front of the engine and remove the timing belt, it's quite a job, or else I would have done it already. I don't hear any strange noises to indicate problems or worn bearings in the pump. It seems like switching to my old cap helped a bit, but it still warms up above normal on low speed hills. My next step is to trim my stock fan shroud and try to mount it to the e-fans, or switch to a volvo/taurus setup which is a rowdy fan that'll damn near fly away if it's not bolted down.
nckwltn
Explorer
I think we remember your cluster photo showing 200k+ miles.... You aren't on the stock water pump... And if it hasn't been done recently, you probably better plan on doing it soon.
The job isn't too bad, but it does take a long time, and some bolts are a pain to undo (ac compressor comes to mind)
The FSM has a good step by step process and the parts are just a few hundred for name brand.
The job isn't too bad, but it does take a long time, and some bolts are a pain to undo (ac compressor comes to mind)
The FSM has a good step by step process and the parts are just a few hundred for name brand.
While I agree that you might want to consider doing the water pump if you don't have any history on it (usually done with timing belt job), I don't think it has anything to do with your problem right now. Unless it is slipping (and in that case I think you would have bigger problems than what you have had so far), the water pump speed changes right along with RPM's. It's working. More RPM's = more coolant flow. Coolant is always circulating around the block regardless of the thermostat's condition. When the thermostat opens it allows some of the coolant to pass through the radiator. I don't think the thermostat is an on/off system, it is variable with temperature. The hotter the coolant, the further it will open.
MummifiedCircuitry
Adventurer
Good news, I tracked down the email correspondence with the previous owner when we were discussing the truck and found this:
4) Timing belt, crank shaft position sensor, and water pump were all replaced about 15-20K miles ago.
5) Only twice has the car gotten hot and boiled coolant out of the reservoir. Both times, I was towing our 23’ camp trailer. It has never gotten hot at any time other than those two times. There is NOT water in the oil or oil in the water, or white exhaust. The coolant that boiled out looked old/dirty, so I flushed the radiator multiple times, and it’s better, but I would not tow again with it without replacing the radiator. There are no known coolant leaks.
I spoke with the gentleman for a few weeks before purchasing and he mentioned every SINGLE little issue with this rig before I bought it. He was an extremely honest guy, so I really do trust what he says unlike most people I've bought vehicles from. I knew it had a newer timing belt because I remember the conversation when I was inspecting the vehicle, but I had forgotten anything about the water pump.
4) Timing belt, crank shaft position sensor, and water pump were all replaced about 15-20K miles ago.
5) Only twice has the car gotten hot and boiled coolant out of the reservoir. Both times, I was towing our 23’ camp trailer. It has never gotten hot at any time other than those two times. There is NOT water in the oil or oil in the water, or white exhaust. The coolant that boiled out looked old/dirty, so I flushed the radiator multiple times, and it’s better, but I would not tow again with it without replacing the radiator. There are no known coolant leaks.
I spoke with the gentleman for a few weeks before purchasing and he mentioned every SINGLE little issue with this rig before I bought it. He was an extremely honest guy, so I really do trust what he says unlike most people I've bought vehicles from. I knew it had a newer timing belt because I remember the conversation when I was inspecting the vehicle, but I had forgotten anything about the water pump.
MummifiedCircuitry
Adventurer
I did them all at once, I was sure one of them would fix the problem. I feel like the engine runs hotter than most, so a small change such as maybe not enough air flow or no shroud is making just enough difference to heat up too much. I'm going to attempt to trim the shroud to fit my electric fans and see if that helps. I took it out for 2 drives yesterday after putting my old cap back on and it didn't get hot in some of the places it usually does, so I think that was part of the problem.