overheating issue

[scout man]

I am having a problem with the scout 345 v8. It keeps overheating at an idle. Started a few months ago, and seems to be becoming more of a problem. I can cruise up a mountain pass at almost redline with no problem, but if it sits and idles for a few minutes the coolant will boil out of the reserve reservoir. I even have an auxilliary electric fan in front of the radiator, and even with that on it will over heat at idle. I noticed the last time it happened, that the upper radiator hose was bulging really bad, and about to explode. Also frightening, I noticed last time that the fuel in my inline filter, which is at the front of the block, appeared to be boiling. I am not hugely knowledgable when if comes to engine stuff. SO what am I probably looking at here, water pump? clog somewhere? thanks!

[Rmart74]

I am no mechanic, but if your coolant is boiling I think it may be a clog somewhere as it is letting the fluid sit to a boiling point. Sorry I cannot be more help.

[Rob]

I think it may be a clog somewhere

I'm no mechanic, either, but that'd be my vote.

[Robert B]

the weird part is if ur moving its fine??? maybe the water pump is working then for somereason but not at idle ?? or it is pumping badly and at redline the speed it is turning is overcoming the bad pumping ?? ahh i know its kinda waste of gas but can you sit still and run it at say 2 or 3 thousand rpm for a few mins and its fine ??? but let it drop to idle and see if it will then overheat ......

[Cr33p3r]

it could also be the t-stat has a weak spring and while moving it has enough rotational force (pumping coolant) to hold the stat open and while stopped it does not and lets the stat close causing it to overheat.

[Chris]

The primary function of the fan is cooling at idle so it's probably the t-stat. A clog wouldn't be selective and happen only at idle. Lots of hot rods run w/o a fan just fine because the driver shuts of the motor at idle. Keep it simple and start with the t-stat Steve.

[Hypoid]

Does it still have the fan shroud?

[wakkjobb]

Which way does the aux fan move the air? Also one vote for thermostat, start easy.

Edit:
After re-reading this, it reminds me of a Camaro I had that did the same thing. It ended up being the water pump. When moving, the airflow would cool the radiator fine but when stopped (no flow) it would get hot as crap. If you end up replacing the pump, it's a good idea to replace the hoses/t-stat as well since the excessive heat will have damaged them and shortened their lifespans.

>>Dan

[Patrolman]

My vote has the water pump. At least that is my first thought. For some reason it likely isn't moving the coolant at idle, but able to spin enough at higher RPM. It is possible the impeller is damaged or corroded. Either that, or there is a clog keeping the coolant from moving quickly enough, but I would lean toward the water pump. Good news is that it is easy to get to on these engines. This article makes several other good points as well...

http://www.ehow.com/about_6317755_car-overheat-idling_.html

[Hypoid]

I still think it's air flow, but, how old is the radiator cap?

[Roostercruiser]

That's what mine doing
It was a blocked radiator. Works great now
$75 to have it dipped
.

[ROKTAXI]

Radiator cap???

[scout man]

It does not have a fan shroud on it, but hasnt since I bought it, and this is a new issue.

The aux fan is on the outside, but is definitely blowing air through the radiator. The mechanical fan is still active as well.

I have heard some thioughts here that were along the lines of my thinking. I was thinking the pump is not pumping, but when I am moving it doesnt matter because it is still getting cool enough... or the pump is picking up a little bit at speeds. Ill have to dig into this and get it fixed before moab. thanks.

[4finger]

but when I am moving it doesnt matter because it is still getting cool enough...
maybe because of the winter temp wind flowing around the engine??????? honestly, just a thought. im not as good with engine compartments as i should be.

[Hypoid]

What I know at this point is that the cooling system is not shedding enough heat at idle. 4finger has a valid point about the ambient temps being cooler over the past few months. Ever notice the cars on the side of the highway when the average temps change by 20 or 30 degrees? Some problems can be masked by weather trends.

If the water pump was losing it's capacity to move fluid, the engine would overheat under load. That's not happening.

If the thermostat were stuck closed, the engine would overheat quickly, under most any operating condition. If the thermostat were stuck open, especially in that big iron block, the engine would never reach operating temperature. A small aluminimum engine would be more likely to overheat with the T-stat stuck open.

What you have told me at this point, is that the cooling system has a diminished threshold for shedding heat. That narrows the problem down to adequate airflow, or reduced surface area inside the radiator. I'm leaning towards Rollies suggestion, but recommend removing the electric fan from the vehicle to see what happens. I've read more than a few threads started by someone who thought an electric fan would cure any percieved problem, only to be disappointed. If the engine still overheats at idle, while the engine is running, touch the front of the radiator to see if there are any cool spots. An area that is cooler while the engine is running is likely to not have any coolant flowing through it.

Did you ever look at the underside of the radiator cap?

Does this beast have a clutch fan?

Any problems with driveability, does it act sluggish?

[scout man]

touch the front of the radiator to see if there are any cool spots. An area that is cooler while the engine is running is likely to not have any coolant flowing through it.
WIll do.


but recommend removing the electric fan from the vehicle to see what happens
The fan has been on there for a long time. I am not convinced that the fan has made a difference, since it was on there a long time without creating and overheating issue. It was added on just for the extra air flow while crawling at low RPMS.


Did you ever look at the underside of the radiator cap?
No, what am I looking for?


Does this beast have a clutch fan?
No, fan is always on when the engine is running.


Any problems with driveability, does it act sluggish?
Its always sluggish, but I havnt noticed it being worse than usual

EDIT: thinking back on it, it maybe has been a little more sluggish than usual.. hard to say

[Patrolman]

I don't believe any of the Scouts have a clutch fan. I would have to look to confirm. Just FYI, a clutch fan is built into a mechanical fan. You can then spin the fan by hand with the engine off. One that does not have a clutch fan wouldn't spin by hand with the engine off. It is basically a direct drive then and has to spin the belts in order to move.

The underside of the radiator cap should be in good shape. No cracking of either rubber gasket, etc. I had one with a really good split in the lower gasket. The lower gasket keeps the pressure to keep the radiator from boiling over at normal operating temps, since it is under a certain PSI. If it is cracked or worn, it can't hold that PSI. The upper gasket allows the radiator to draw coolant back in from the overflow tank rather than the outside air. Also forces the coolant into the overflow when it warms up.

My understanding is that the cap wouldn't be the problem. There isn't coolant gushing all over the place and boiling out. Also, the coolant level seems to stay at the proper level when checked cold. Sounds like the only problem is it runs warm and the hose starts to bulge...

[scout man]

There isn't coolant gushing all over the place and boiling out. Also, the coolant level seems to stay at the proper level when checked cold. Sounds like the only problem is it runs warm and the hose starts to bulge...

Actually it does boil out. It overheats and boils out of the reserve reservoir.

[Patrolman]

In that case, I would just replace the cap. It can visually look good, but still be bad. They can be tested for PSI, but frankly, for a few bucks, a new one might be in order.

[scout man]

thanks, Ill do that and see where it gets me.

[Robert B]

It can visually look good, but still be bad
yes my truck had one of these (only part of my prob)

[Hypoid]

The underside of the radiator cap should be in good shape. No cracking of either rubber gasket, etc. I had one with a really good split in the lower gasket. The lower gasket keeps the pressure to keep the radiator from boiling over at normal operating temps, since it is under a certain PSI. If it is cracked or worn, it can't hold that PSI.
Yup! Raising the pressure, raises the boiling point. It's pretty common to have someone say that their car is overheating when it's just a cap that needs replaced.

When you check the radiator for cool spots, you are looking for coolant tubes that are clogged. The cool spot would run from tank to tank.

The thought behind the sluggish engine can stay under my hat for the time being. I've only seen it once, and it was not the primary cause of that vehicle's problems.

[scout man]

so, now that I have had a chance to look closer, it does actually have a clutch fan, and I noticed the fan was spinning REALLY slow at idle. I think the clutch is bad. Question.. is it possible to just weld up the fan so its no longer a clutch fan? or, how hard is it to replace... I also have another engine in the garage that has a fan without a clutch that I could maybe swap in... but I dont like that fan as much. thoughts?

[Patrolman]

Should just be 4 bolts to undo the fan. Easy to do. I think you can swap in a non-clutch fan. If you just want to buy one, here is one.
http://denver.craigslist.org/pts/2253604013.html

[scout man]

hahaha, I have been looking at that damn guys post for a year now, reposted every 4 days, wondering when the hell he would just give up.... and now I might need something from him :rolleyes:

Does the clutch vs non-clutch make a big difference for any reason? Would one be better than the other for my application? I am tempted to just try the non-clutch I have sitting in the garage. Only reason I dont like it is it has a non-symmetrical fan on it, but was definitely made that way, which is just weird to me. ill take a pic of it tomorrow

[scout man]

decided to go ahead and take pics now. At first it looks like a blade is missing or bent, but it was definitely made this way, not sure why. Not sure if it will be a problem or not.

[foxtrot]

weird, seems like it wouldn't be very balanced for how fast it spins.

[scout man]

my thoughts exactly. Thats why I am shying away from it until someone tells me there is some logic to it. I mean, its on an identical engine, from one year newer, so I would assume it would work, but you just never know I guess

[Brody]

Steve

Almost all of the rigs that I have had with the exception of a few, have had a fixed blade fan, including a couple that weren't symmetrical like your picture. I have never had any problems with them at all. The design is based on the air flow and I believe that the ones like your pictures are designed that way to flow more air. The main difference in the clutch vs non clutch fan is that the fan offers less drag until your engine reaches a certain temp and also allows the fan to 'freewheel' when it isn't needed. It is also a 'quieter' fan.

The non clutch designs starts spinning as soon as your engine starts, which causes drag, and also causes the engine heater to take more time to warm up as it forces cool air through the radiator as soon as it starts spinning. Also a non clutch fan is spinning all the time, whether your engine needs the cooler air or not. Take for instance driving along the highway when the temp is cool. Your fan may not be needed due to the cooler air being pushed through the radiator. A clutch fan will stop and freewheel, while the non clutch fan will simply continue to pull the air through the radiator. A lot of the clutch style fans are also tied into a thermostat control of some sort so that the clutch 'knows' when to engage or disengage.

I am using a thermostat controlled fan on the Yota as an extra fan for slower crawling. I got rid of the thermostat control and wired it up to a simple on/off switch so I can simply turn it on and off as needed to keep the temps down.

Here is a very good article that explains it a little better than my explanation:

http://www.rowand.net/shop/tech/ThermostaticClutchFan.ht

If it were me. I would just mount the non complicated fan (read: one less thing to go wrong, cheaper to replace..) and deal with the slower warm up times. The difference isn't that much.

[scout man]

that explanation makes sense, but also makes me wonder. I think I need to let the engine warm up then and see if the clutch ever engages, if not, it could possibly be the thermostat? Obviously it could still be the clutch too. I probably will just mount the solid fan, because like you said, it is just a lot less to go wrong

[Patrolman]

My 74 Scout with the 258 had a fixed fan, as do all the Nissan Patrols that I have had. All other vehicles I have had were on a clutch.

The BIGGEST reason to go with a clutch in my opinion is for water crossings. With a clutch the fan can actually stop while the engine is running. When I was in ASE classes, the teacher (smart guy) said you can actually start an engine with a fan clutch and hold the fan still while the engine runs. It is all centrifical force, and it can't overcome someone holding it. On the other hand, don't put your hand in there when it was already spinning. That would be a bad thing. SO, with water crossings, the water can essentially stop a fan. With one with a clutch, no problem. With a fixed fan, it basically becomes a boat propeller and drives forward into the radiator, completely shredding the radiator. Bad idea...

[scout man]

makes sense. I am not horribly worried about it, since that would have to be some pretty darn deep water to hit my fan, but good to know.

[Robert B]

oh and steve since my fan is now easy to see since the shroud is out my fan has that same nonsymetrical design to it and its run fine for the last couple months and 3 trails :) so it is normal