Overheat coolant - SD25 D21 1987 Nissan

[asavage]

this morning i looked under the hood and discovered that the resevoir was full but the rad was low.

The usual reason for full reservoir and low coolant in radiator is an air leak. As the coolant expands, it goes to the overflow reservoir. When the engine cools, a vacuum is formed but if there's a leak, air is drawn in instead of pulling coolant from the reservoir.

Some leaks, esp. at the water pump seal, can leak a lot in one direction (under vacuum) and little in the other (under pressure).

Food for thought.

Another thing: it's very common for there to be residual air in a cooling system after it's been opened up, that works its way out to the reservoir. That's why the reservoir's level commonly drops quite a bit after cooling system work: you start out with it full, and it blows air out of the cooling system into the reservoir as it's running, pulls coolant from the reservoir back into the cooling system as it cools.

The vacuum evacuation method I mentioned earlier alters that behaviour, because there's almost no air left to "work out" when you begin with a partial vacuum when refilling the cooling system.

SDs do not seem to trap much air though. If you continue to have to fight this, I'd suggest disconnecting the coolant loop for the WVO system for a few days, to see if the symptom changes.

[philip]

-SNIP- The hoses all seemed proper, very hot to the touch. the rad is cold near the top, warm elsewhere.

Is the ambient temperature very cold out? How can the radiator be "cold near the top" while "all the hoses are very hot to the touch"? This alone suggests coolant trying to enter the radiator is being restricted or displaced.

I stopped and turned the rad cap to release pressure and lots of bubbles were sent to the resi.

This is normal ... once or twice. Continued air/gas/pressure accumulation will result in overheating because coolant will be forced to the overflow tank.

I remind you that the rad specialist tested for combustion gasses coming from the rad with a colour/fluid test

Whoopie doo. As I recall ... those testors are for carbon monoxide which diesels produce very little. That's why there is a different test fluid for diesel. Maybe the radiator guy doesn't know.

Diesel-specific combustion gasses detector, Lisle No. 75500, $28, $37
http://www.sjdiscounttools.com/lis75500.html
http://www.autobarn.net/licoledefl.html

Diesel-specific testing/detecting fluid, Lisle No. 75730, $6
http://www.sjdiscounttools.com/lis-75730.html

[after oil]

Is the ambient temperature very cold out?

its been 45-5o today

How can the radiator be "cold near the top" while "all the hoses are very hot to the touch"? This alone suggests coolant trying to enter the radiator is being restricted or displaced.

where does it displace to?

there is a different test fluid for diesel. Maybe the radiator guy doesn't know.

the fluid bottle said one colour for gasoline gases and another colour for diesel gases

Whoopie doo

thats funny.
this guy has been in business over 40 years in the same location. his family, originally chinese immigrants, are the oldest business owning family in town. off topic, sorry

[after oil]

today's update:

today the truck behaved pretty much as it has been behaving, and i fooled around with it the way i have been.

the wvo heating system has been removed from the equation.

the water was low in the rad. so i filled it just till i could see water collecting above the top of the fins. the engine warmed and the rad bubbled a bunch.
i opened the plugged coolant-to-wvo-heater tee to let air and fluid pass through. the temp gauge was much higher than normal. the hoses were hot, but not the rad.the lower rad pipe heated up.
but the rad isnt heating up.

i let some pressure off here and there.

temp gauge returned to normal, things seem fine again.

checked after the engine cooled and the rad is low again.

[after oil]

asavage wrote:

Some leaks, esp. at the water pump seal, can leak a lot in one direction (under vacuum) and little in the other (under pressure).

hmmmm...

today she got real hot, according to the temp gauge, just parked but under load sometimes. the engine got hot, but not the heater hoses or the rad.

the rad was definitely under pressure, and the fluid and gasses that came out were not hot.

i was considering now bypassing the heater.

i hope i havent worn out my welcome here with this one. ive been dealing with this for over 2 weeks!

[philip]

This problem is not complicated. For two weeks worth of foolin' around ... nothing has been accomplished. Take the truck to your respected radiator professional and spend the money to get an accurate diagnosis. Posting more observations here won't fix it.

[after oil]

This problem is not complicated

this morning a mechanic took one look and suggested that my fan belt was worn, and not always engaging the water pump. he said the pulley looked like it came from a tractor and it didnt fit the belt just right. the belt is fairly new.
i replaced the belt, and everything seems a-ok ,for now. i took it for a long drive, and went up a bit of a mountain on a logging road.


ill see about posting a photo of the pulley

[asavage]

I don't know about the sheave, but the water pump sure looks different from the 720's SD. I'd like to see a pic taken just a little bit further out.

[philip]

This problem is not complicated

This morning a mechanic took one look and suggested that my fan belt was worn, and not always engaging the water pump. he said the pulley looked like it came from a tractor and it didnt fit the belt just right. the belt is fairly new.

This "mechanic" of yours is ... clueless. With a loose drive belt, the ALTERNATOR is going to slide first. You would have squalling belt noise in the morning while the system recovers from the glow plug and starter drains.

[after oil]

well, anyway, it seems not to be fixed. i might get the rad pulled out and tested on friday

[asavage]

today she got real hot, according to the temp gauge, just parked but under load sometimes. the engine got hot, but not the heater hoses or the rad.

It is very difficult to get a diesel hot at idle. What do you mean, when you say, "under load sometimes".

This problem does not feel to me like a radiator with diminished capacity. Those get gradually worse, and only under a significant load. It's winter up here! I assume (as you're only a couple of hundred miles north of me) that you are seeing relatively the same weather temps as I.

Given that, I would not be suspecting the radiator.

Have you performed a cooling system leak-down test? This device attaches to the radiator where the cap resides, has a hand pump and a gauge. Pump up the pressure to 15 PSI (engine off), and watch it. Do this on a warm engine, you might find water in the oil, or a leak where you didn't expect one.

Any place that services radiators will have a cooling system pressure check device such as this. We had three (for the various adapters for different radiators).

Cooling system pressure tester

[after oil]

by under load i mean i'm holding the throttle open part way.

Have you performed a cooling system leak-down test?

yes. that was done pretty early on. today someone said i should try it with the injectors out.

the weather here is pretty decent. colder today.

[after oil]

22 days since my first post. if this is supposed to be simple.....?

with new thermostat, temp gauge reads H for a few km, then returns to normal

pressure builds, releases out the resevoir. gasses or steam are displacing coolant.

two areas i want to discuss right now: fan and head

fan: what makes the fan turn?
is it always supposed to turn?
a heat activated clutch?
a sensor that turns it on?

whats it doing you may ask? when the engine is warm, (but off of course) it spins a little when i spin it. engine cold: i can turn it, but theres drag, so it doesnt spin. it turns freely from the pulley. (ie i can turn the fan but not the pulley)

head:

The SDs do not have a history of leakage at the head gasket area, even when overheated.

If you run the same coolant for four, five or even more years, corrosion will happen, and the head gasket interfaces are vulnerable.

i dont know the history of the rad, ive had the truck 1 1/2 years only. the rad guy says it aint blocked at all.

a parts guy says there could be a crack in the cylinder head.

someone suggested torquing down the head.

thanks, after oil

[philip]

22 days since my first post. if this is supposed to be simple.....?

I sense stress.

With new thermostat, temp gauge reads H for a few km, then returns to normal

Pressure builds, releases out the resevoir. gasses or steam are displacing coolant.

Signs of overheating ... insufficient coolant flow and/or gases displacing coolant.

Two areas i want to discuss right now: fan and head

fan: what makes the fan turn?
is it always supposed to turn?
a heat activated clutch?
a sensor that turns it on?

1. Rotation transmitted through a viscous fluid.
2. It always will turn but ... at an rpm less than the water pump pulley. The amount of slippage is governed by a thermostatic viscous clutch and engine RPM.
3. When there is a coil spring or a bi-metalic spring on the clutch, then yes ... by temperature. But RPM also plays a very significant roll.
4. See #3.

Whats it doing you may ask? when the engine is warm, (but off of course) it spins a little when i spin it. engine cold: i can turn it, but theres drag, so it doesnt spin. it turns freely from the pulley. (ie i can turn the fan but not the pulley)

Normal.

I dont know the history of the rad, ive had the truck 1 1/2 years only. the rad guy says it aint blocked at all.

A parts guy says there could be a crack in the cylinder head.

Someone suggested torquing down the head.

thanks, after oil

What do the church ladies say? This vehicle with an SD diesel is NOT going to overheat in the manner you have described at length PROVIDED:

1: The radiator is actually good
2: The thermostat is the correct part and actually good.
3: The water pump is sound and the drive belt properly tensioned.
4: The hoses are sound ... not collapsed inside.

I've run my 720 around in the southern california SUMMER with the A/C ON and experienced no overheating until stuck in 95*+ weather at speeds under 25 mph ... WITH NO FAN INSTALLED. So use that as your baseline.

That you continue to get air/gases blowing coolant into your reservior over short driving distances tells you what's haywire.

[asavage]

If I read that right, Philip, you are suggesting that there is a combustion gas leak into the cooling system, one that the previous (diesel) fluid test didn't catch.

Head gasket or crack, eh? Sounds like Snakelady's problem again, possibly.