Avoided an engine disaster yesterday

[V8Limited4wd]

So I recently had my timing belt and water pump replaced, along with the radiator, a/c condenser, thermostat and all the hoses - basically the entire front end of the engine. I had it done by my brother who is a mechanic who did it for free - just gave him money for the parts. After driving Bessie back to VA from Philly, I checked the coolant tank and noticed it was low, so I filled it back up. I also noticed that the top radiator hose had moved a little on both ends. For the next three weeks I drove it around while constantly checking the coolant tank and refilling it, as well as adjusting the hose. So I was able to determine the leak was coming from the Koyo radiator - so I figured, oh it's a bad radiator so that will be easy to replace.

The other day I was sitting in traffic after picking up my daughter from daycare, and I hear this loud POP from the engine bay and see steam coming out. Thankfully I was near a huge exit ramp and pulled over to the shoulder. I open the hood and saw that the top hose detached from the radiator and sprayed coolant everywhere. Luckily I had my leatherman tool and extra coolant, and even more lucky that the engine didn't overheat.

Turns out the thermostat was stuck closed, causing excessive pressure in the system. This caused the radiator to start leaking, and also a tiny leak in the area under the intake manifold where the thermostat is. I'll be driving up to Philly to get the radiator and thermostat replaced, but was told to have the thermostat completely removed before driving up. I didn't think the thermostat was an issue since the engine temp always stayed in the middle the entire time I was driving. Apparently it is still able to release the heat through the heater core. And since most of my driving was on the highway, it kept the coolant temp/pressure low enough.

Anyways, just wanted to share just in case anyone else is having similar issues after replacing their radiator/thermostat. I really dodged a bullet there.

 

[RonJR]

Sounds to me like the upper hose wasn't clamped down properly. You mentioned it "moving around".

The pressure cap should relieve pressure at about 14psi, so there is no way a stuck thermostat can generate enough pressure to blow a properly installed, healthy coolant hose.

 

[pjku79]

I agree with Ron.

 

[V8Limited4wd]

Sounds to me like the upper hose wasn't clamped down properly. You mentioned it "moving around".

The pressure cap should relieve pressure at about 14psi, so there is no way a stuck thermostat can generate enough pressure to blow a properly installed, healthy coolant hose.

I would check the hose clamp everyday and make sure it was on tight. So you think maybe the pressure cap is bad? And he had put in the OEM red undiluted coolant. Would that also cause more pressure in the system?

I'm just wondering what caused the excess pressure in the system which probably caused the leak in the radiator and forcing the hose to pop off.

Just sucks after all these years of reliability I'm having this kind of issue. I hope I can figure this out.

 

[RonJR]

There's a ridge (or should be) on the stub pipe out of the radiator, that the coolant hose slides over. The clamp goes on the radiator side of the ridge, so that, when properly tightened, the clamp and hose can't slide off the pipe. If the clamp was inadvertently placed on top of the ridge instead of behind it, you'd get an unstable (moving) connection and a high probability of blowing off under pressure, no matter how tight the clamp was cranked down.

I'm still thinking improper hose installation. Glad you caught it immediately when it blew.

 

[V8Limited4wd]

There's a ridge (or should be) on the stub pipe out of the radiator, that the coolant hose slides over. The clamp goes on the radiator side of the ridge, so that, when properly tightened, the clamp and hose can't slide off the pipe. If the clamp was inadvertently placed on top of the ridge instead of behind it, you'd get an unstable (moving) connection and a high probability of blowing off under pressure, no matter how tight the clamp was cranked down.

I'm still thinking improper hose installation. Glad you caught it immediately when it blew.

Yup I know exactly what you're talking about. I made sure that the clamp was in front of the ridge. So maybe I need to get new clamps? Now the hose moved on both ends, but popped on the radiator side.

 

[RonJR]

You can easily have the pressure cap tested at Autozone, etc., or just buy a new one for a few bucks if you don't trust it. Normally they fail the other way - they don't hold enough pressure, rather than failing by refusing to release pressure.

I'm also skeptical that the thermostat was really stuck, since the coolant temperature remained normal. The thermostat is what regulates that temperature, and the valve mechanism has to be moving to do so. Think of it this way. When you start your engine in the morning, the thermostat is closed. How long does it take for the coolant to go from ambient temperature to 180 deg (normal operating temp)? About 5 minutes max. If the thermostat stayed closed, the temperature would just keep climbing at that same rate and you'd be overheated, with the gauge in the red, in less than 10-15 minutes.

 

[V8Limited4wd]

You can easily have the pressure cap tested at Autozone, etc., or just buy a new one for a few bucks if you don't trust it. Normally they fail the other way - they don't hold enough pressure, rather than failing by refusing to release pressure.

I'm also skeptical that the thermostat was really stuck, since the coolant temperature remained normal. The thermostat is what regulates that temperature, and the valve mechanism has to be moving to do so. Think of it this way. When you start your engine in the morning, the thermostat is closed. How long does it take for the coolant to go from ambient temperature to 180 deg (normal operating temp)? About 5 minutes max. If the thermostat stayed closed, the temperature would just keep climbing at that same rate and you'd be overheated, with the gauge in the red, in less than 10-15 minutes.

That's what confuses me. The temp needle didn't budge past the center the entire time driving it. I had taken a recent trip to Philly to take a look at the leak and he told me he noticed a lot of pressure in the front hose. He told me that some fluid did bypass enough to maintain the engine temp, and that the heater core also dissipated the heat - so maybe it's opening enough to let some coolant through but not opening all the way. I'm driving up to Philly next week to drop it off for a month, hopefully it all gets fixed during that time.

 

[Whammy]

Glad you caught it! Hopefully you can fix it soon!

 

[V8Limited4wd]

So I took a 3+ hour trip to Philly again with stop and go traffic. I was a bit anxious about it but I checked the hoses after the drive and they haven't moved at all. I did notice some coolant that leaked out around the neck of the coolant tank line right below the radiator cap. So that means that the cap is releasing pressure, but the hose probably needs to be replaced. I'm guessing there was an air pocket that caused the top hose to come off the radiator. Hopefully after my brother replaces the radiator and the thermostat everything will be good to go. Only reason why I'm holding on to the 4Runner is because of its reliability!

 

[catrains]

I would check the hose clamp everyday and make sure it was on tight. So you think maybe the pressure cap is bad? And he had put in the OEM red undiluted coolant. Would that also cause more pressure in the system?

I'm just wondering what caused the excess pressure in the system which probably caused the leak in the radiator and forcing the hose to pop off.

Just sucks after all these years of reliability I'm having this kind of issue. I hope I can figure this out.

I had the pressure cap not release pressure . so what happened was the engine ran a little hotter and the upper rad hose was expanding too much . I squeezed the hose and I felt it was too hard .. this happened gradually during the summer as the temps got higher .. I cleaned the radiator cap and the pressure dropped / hose not hard.. then I also replaced the upper hose since it did get damaged from the pressure ..

I would clean/replace the pressure cap... then see if the hose is with less pressure when hot.

 

[nevada]

So I took a 3+ hour trip to Philly again with stop and go traffic. I was a bit anxious about it but I checked the hoses after the drive and they haven't moved at all. I did notice some coolant that leaked out around the neck of the coolant tank line right below the radiator cap. So that means that the cap is releasing pressure, but the hose probably needs to be replaced. I'm guessing there was an air pocket that caused the top hose to come off the radiator. Hopefully after my brother replaces the radiator and the thermostat everything will be good to go. Only reason why I'm holding on to the 4Runner is because of its reliability!

the cap will vent the excess pressure into the overflow bottle. if its leaking at the radiator, the cap IS bad.

also, the thermostat being stuck shut would for sure cause you to overheat the engine. the heater core can take SOME of the heat, but not enough to prevent overheating. also, its august, are you even using the heater now? or is your heat selector set to the cold side? if so, the heater core is being bypassed, no coolant is going through it.

I highly doubt the thermostat is the problem.

 

[V8Limited4wd]

I had the pressure cap not release pressure . so what happened was the engine ran a little hotter and the upper rad hose was expanding too much . I squeezed the hose and I felt it was too hard .. this happened gradually during the summer as the temps got higher .. I cleaned the radiator cap and the pressure dropped / hose not hard.. then I also replaced the upper hose since it did get damaged from the pressure ..

I would clean/replace the pressure cap... then see if the hose is with less pressure when hot.

Well I'm getting the radiator replaced, so I'm guessing it will come with a new radiator cap. I'm thinking that the cap is the issue too. Thanks for the info!

 

[V8Limited4wd]

the cap will vent the excess pressure into the overflow bottle. if its leaking at the radiator, the cap IS bad.

also, the thermostat being stuck shut would for sure cause you to overheat the engine. the heater core can take SOME of the heat, but not enough to prevent overheating. also, its august, are you even using the heater now? or is your heat selector set to the cold side? if so, the heater core is being bypassed, no coolant is going through it.

I highly doubt the thermostat is the problem.

Yeah I agree, if it was the thermostat, the temp would have gone up a little with the summer heat and stop and go traffic. Doesn't the coolant still go through the heater core even if the heat is not being used?

 

[catrains]

Yeah I agree, if it was the thermostat, the temp would have gone up a little with the summer heat and stop and go traffic. Doesn't the coolant still go through the heater core even if the heat is not being used?

coolant flow is always threw the heater core.......

there are some that install a shutoff coolant control valve on other cars in the very hot regions so that the ac puts out colder ..engine vac coolant control valves were used in older vehicles a long time ago.

I knew one person 40yrs ago that would disconnect the vac line to this valve in the summer heat ..then when it got cooler connect it back up.

did not effect engine temps.

 

[nevada]

Yeah I agree, if it was the thermostat, the temp would have gone up a little with the summer heat and stop and go traffic. Doesn't the coolant still go through the heater core even if the heat is not being used?

maybe. but even if it did, there is no air blowing across it to remove heat. it wouldn't do anything to prevent overheating.

coolant flow is always threw the heater core.......

there are some that install a shutoff coolant control valve on other cars in the very hot regions so that the ac puts out colder ..engine vac coolant control valves were used in older vehicles a long time ago.

I knew one person 40yrs ago that would disconnect the vac line to this valve in the summer heat ..then when it got cooler connect it back up.

did not effect engine temps.

its possible it no longer has a control valve. I haven't actually looked. I do know that pretty much every vehicle used to have them.

 

[RonJR]

The heater core is probably less than 1/10 the size of the radiator, plus the heater fan (even when it's on and pulling air through the core) moves much less air than the radiator fan.

Bottom line, the heater core can't begin to cool your engine. If the thermostat is stuck closed, you will overheat, and rather quickly. Conversely, if you're not overheating, the thermostat isn't stuck closed.

 

[catrains]

maybe. but even if it did, there is no air blowing across it to remove heat. it wouldn't do anything to prevent overheating.

its possible it no longer has a control valve. I haven't actually looked. I do know that pretty much every vehicle used to have them.

the new vehicles I have worked on have temperature doors. I have had to fix a few . the doors can stick, the step motors can fail, the venting plastic can distort over time and the heat causing them to bind.

if the two heater hose pipes are hot [under dash] then there is no control valve with the ac on max cool..............

 

[nevada]

the new vehicles I have worked on have temperature doors. I have had to fix a few . the doors can stick, the step motors can fail, the venting plastic can distort over time and the heat causing them to bind.

if the two heater hose pipes are hot [under dash] then there is no control valve with the ac on max cool..............

yeah, blend doors. older rigs had those too.

right. thanks. I am aware on how to check. like I said, I haven't.


either way, the heater core isn't enough to keep it from overheating. especially if the t-stat was stuck shut.

 

[V8Limited4wd]

Turned out to be a stuck thermostat which was replaced - wouldn't open up all the way as it was at an angle. Radiator stopped leaking as well. Hope that solves the problem!