Thermostat Leak?

heating

#1

I have a 95 Nissan Pathfinder (VG30E 6 cyl.) that under-heats. I changed the thermostat which seemed to be OEM. I checked the new and old in hot water and the OEM seemed OK. I put the new one in and… same problem.



It can’t be stuck open twice. I stuck my finger in the radiator then started the car and the coolant started warming in less than 60 second. It’s the only test I could think of!!! It appears that it is letting the coolant leak by it. Why would the thermostat leak? I’m the third owner, so I don’t know if it was ever changed. I doubt it did this from the time that it was new.


#2

Why do you think it is running cool? Maybe it is running at the correct temperature, but the gauge or whatever you are using to determine the temperature is low, is the problem.


#3

It is REALLY cold in the winter. I could run it for 20 minutes and it would not warm up. Of course it was 2 degrees out…

However, the heat blows HOT when the gauge comes up to normal. Hot enough to make your hand uncomfortable like my Altima. It heats up way faster in warm weather. Still not as fast as normal. This is my second Pathfinder. Last one was in AZ, this one in PA.

Also, in addition to my wacky finger in the radiator test, when you start it cold and rev the motor you can see coolant flowing.

So, I’m 75% sure I know what is going on…but WHY is it happening. I can’t just keep changing the thermostat. It is REALLY hard to get the bolts in!


#4

Dumb question: are you sure the thermostat is installed in the correct direction? I bought a car several years ago that was running to cool, when I replaced the thermostat, the installed one was backwards, it would have been easy to instal the new one the same way.


#5

Craig:
The only reason that is a dumb question is because if you put a t-stat in backwards the car would over heat.


#6

Craig:
The only reason that is a dumb question is because if you put a t-stat in backwards the car would over heat.

Interesting, but wrong. If you knew what engine I was discussing you might understand.

I don’t know how the cooling system on the OP’s engine is designed, but on some engines installing the thermostat backwards is possible and can cause flow to bypass to the radiator when the engine is still cold. An overcooling condition is almost always related to some problem with the thermostat.


#7

Did it ever work right for you? You may have some restriction in the normal recirculation path that exists to warm the engine when the tstat is closed. This causes increased water pressure and overcomes the spring pressure of the tstat.


#8

2 degrees? When I lived in North Dakota we used to have to put cardboard or a blanket in front of the radiator to get the engine to warm up enough to get some heat when the outside temp was near zero. Since the engine is heating up, as evidenced by your description of the output from the heating vent, I’m incline dto suggest that the system is operating normally.

Or am I missing something? Darn it’s hard to write answers without being able to see the post I’m answering!

  • mountainbike

#9

Had to think for a second…

I don’t know if this motor is an odd design, but the thermostat is where the water returns from the radiator, it is attached to the suction tube (as I think the technical term is…). Rather than let water into the radiator it opens so it can suck water out of the radiator. I had to run this through my mind a couple times…I don’t understand why if you take the cap off and rev the motor it doesn’t blow coolant all over. Maybe because you keep the same volume in the motor all the time and it doesn’t have any left over to blow???

My Haynes manual only has a diagram for Nissan’s 4 cyl. But I am fairly sure I am correct.


#10

It doesn’t work that great at 50 degrees either. Also, I owned a Pathfinder just like it in Arizona and it could get down into the 40’s at night in January…that motor stayed warm.


#11

My theory is that the t-stat is not seating correctly. But if the one I pulled was the original (It was an OEM part at least…)why was it doing the same thing?

How do you make sure that it is seating correctly without having to keep disassembling/reassembling the front of the motor?


#12

Oh, yeah. I installed the large side toward the engine block. That diagram is in the Haynes manual. I followed their directions. The bolts, however, are very hard to get in, which leaves the possibility that it didn’t seat right…but again…we come back to the original one not working either…


#13

It’s probably installed correctly if it isn’t leaking. I guess it’s possible, but unlikely, that both are bad. Maybe someone who works on a lot of nissans has seen this before.


#14

Craig:
It is my understanding that when you install a thermostat you install the spring end into the engine side of the t-stat housing correct?
The purpose of the t-stat is to block the flow of coolant from the block to the radiator correct?
If the t-stat is closed no circulation. water in the block stays in the block and water in the radiator stays in the radiator correct?
Tell me what car uses a t-stat to allow water to stay trapped in the block when installed properly but allows constant unrestricted flow when installed backwards.
Come on smart guy enlighten us fools.


#15

Tell me what car uses a t-stat to allow water to stay trapped in the block when installed properly but allows constant unrestricted flow when installed backwards.
Come on smart guy enlighten us fools.

Ok I’ll try to enlighten, the car is my 82 benz 300D (617 diesel engine). The cooling system design is probably a little different from what you are used to, there is a bypass line associated with the thermostat housing so the position of the thermostat does not simply open or close the flow to the radiator, it also controls the bypass flow around the radiator. In other words, the thermostat functions like a 3-way valve and controls both the flow through the radiator and the bypass. It just so happens that installing it backwards allows additional flow through the radiator, resulting in the engine running about 20C too cool.


#16

Craig:
Please provide more information.

It just so happens that installing it backwards allows additional flow through the radiator, resulting in the engine running about 20C too cool.

When you put the t-stat in backwards it makes the hoses bigger? It makes the water pump turn faster? How does it allow additional flow? Also if the spring is on the radiator side how does it ever open? How does the car disipate the heat from the coolant block? Please help me understand as I am just simple folk that don’t understand fancy foreign cars.


#17

When you put the t-stat in backwards it makes the hoses bigger? It makes the water pump turn faster? How does it allow additional flow? Also if the spring is on the radiator side how does it ever open? How does the car disipate the heat from the coolant block? Please help me understand as I am just simple folk that don’t understand fancy foreign cars.

Assuming that you actually want to know, I will explain how the system works. I put the pages from the FSM on a web site here:

http://homepage.mac.com/cbaronxxx/PhotoAlbum5.html

If you look at the diagram, you will see that the thermostats actually has two parts; one in the return line from the radiator to the block, the other in the by-pass flow-path from the block to the water-pump inlet. The thermostat is not installed in the supply to the radiator like most american cars.

When it is cold, the return from the radiator is closed and the bypass line is open. As the thermostat heats (starts opening at 80C, fully open at 95C) it opens the return line from the radiator and closes the bypass line. As you can see from the diagram, installing it backwards would allow flow through the radiator return line all the time (sorta like running an american car with the thermostat completely removed).

When mine was installed backwards, the engine temperature would not get above 60C in cold weather, it’s supposed to run between 80C and about 95C. I doubt the OP has a similar issue on his car, but I was just trying to point out that not all cooling systems are designed the same way.

The actual thermostat looks like this:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.mercedesshop.com/&cookieid=1CQ0J3JZ424X0L0J57&year=1982&make=MB&model=300-DT-001&category=All&part=Thermostat

Hope that helps.


#18

Craig:
Thank you very much for the education on this system. I can see by looking at the pictures you provided that when the t-stat is installed backwards it would have the same effect as not having one at all. This would of course allow full unristricted flow at all times. In fact it appears that if the t-stat is installed backwards you would have additional flow do to the fact that the water no longer flows through the t-stat but around it. I have never had the pleasure of working on this system. Again thanks for taking the time to educate me on the proper operation.
~Michael (Dartman69)


#19

It is a weird design, it can also get people in trouble because they think they can “fix” an overheating car by removing the thermostat (like an american car). Unfortunately, if you remove the thermostat you also open up the bypass and you can actually reduce the flow to the radiator. There are a few things on that engine that are a tad “over-engineered,” but they work.


#20

Woe! The D-man is getting a little snippy… down boy! I started this discussion. Be respectful.

Can anyone find a diagram of the Nissan VG30E motor? I thought about the 3 way bypass deal. I didn’t pay close attention when I installed the last t-stat. It may be how this motor works because, as I posted here somewhere, the t-stat is on the OUTPUT side of the radiator facing in toward the block. But it still makes no sense to me. The flow starts right away. It’s not like it heats up a little then doesn’t work right.

But it is NOT installed backwards. Spring side in, that parts easy. The Haynes book also shows a diagram, but only of the t-stat, housing, and where it bolts to the block. I have searched all over the net and haven’t found anyone with this problem in the VG30E motor. I saw one post about a guy who’s problem sounded similar but the post was 2yrs old with no resolution to the problem.

Some Nissan nut needs to help me out so I don’t go taking apart my motor AGAIN only to have it not help at all! Please!!!