Thermostat Leak?

I should have looked at the pictures first. I need to find a diagram of the Nissan motor like this. It would be consistent with the way this thermostat is mounted - right at the EXIT from the radiator.

OK, so let’s assume this is how the VG30E works…what would cause this? Your Benz had this problem?

The only reason I had the problem was because someone had installed it backwards, your post just reminded me of that. It’s unlikely your engine has the same strange design, it was a long shot. If you installed it per the manual, you should be OK. Honestly, I would find a good independent shop that specializes in nissans, they may have seen this before. Do you know any active nissan forums, they might be helpful.

I guess it’s possible that you got two bad thermostats, but unlikely. If you do want to pull it apart again, you might want to try an OEM thermostat from the dealer, instead of an after-market one. It does sound like you need someone very familiar with the nissan design. Sorry I can’t be more help.

I finally found someone who had a diagram of the cooling system. Googled the correct words!

http://www.cardomain.com/ride/748507/8

It is a very similar if not the same system. Nissan went nuts with complexity on this motor. Could be why this motor has such a reputation for reliability.

Now I just have to make sense of it. I know the t-stat works because I boiled it with the OEM. So now I need to figure out the very complex system. I hope I don’t have to go to Nissan, I’m poor!

Is anyone else intelligent to see what could cause this problem?

Brickhead:
First: let me apologize for overtaking your post. My only intention was to be sure that you were not given incorrect information.
Second: I have reviewed the information you posted and it appears that your nissan has a conventional cooling system. The water pump pumps water through the block, heads, and heater core via the bypass hose until the thermostat opens. After the t-stat opens hot water from the block is allowed to move to the radiator to be cooled and cold water from the radiator is allowed to move to the engine to absorb heat. The only logical explanation I have come up with at this point is that the new t-stat is open.
Before installation did you verify it was closed?
How hot did you get the t-stat when you boiled it?
Did you flush the cooling system when you had it apart?
Did you notice a large amount of rust or anything in the t-stat area while it was apart?
~Michael

I looked at the reference you posted, what a complex maze! Anyway, one of the things I noticed was that it allows some flow through the rad at all times. Perhaps the rad flow is a red herring. I would expect it to be a light flow though and not a gushing stream.

If it were my problem, I might be inclined to try something that would help to isolate the cause. If you were to take one of the old thermostats and make it so it stays shut no matter what, if the engine then heats up normally, you will know for sure it’s opening and allowing flow.

Good questions, I don’t really have much to add.

I still have the t-stat I pulled out. I never checked with a thermometer (didn’t have one handy) but I checked the original and the new one side by side (OEM 170F, Slant 180F - They use the hotter one in Canadian models, and PA is a lot like Canada…as far as cold goes). They had to be close if not right on the correct temp, the water was HOT. I could go check the original one now but I’m lazy.
There is almost no way (despite what it sound like) that it is stuck open. You can see a tiny hint of light through the old one if you look really hard…but… I still think it could be leaking past the new one, but why? The guy that I linked to that had gathered all that data on this motor said to clamp the top radiator hose to verify the problem. How to do that…
I dunno…If I don’t have a conclusive diagnostic test I will have to break down and go to a dealer. I would rather blow $300 now then $1000+ later on a blown motor or head (plus being stuck on the road, in a blizzard, with a crazy AAA tow truck driver…). I can’t risk it. That, and if it IS another cold winter I WILL FREEZE TO DEATH!!!

Well, I understood it!

-Matt

Brickhead, my theory is that if the heater is blowing burning hot air, then you’re not overcooling. The temperature sender may just be reporting the gauge position wrong. What’s the margin here? How far off of the correct temperature is the gauge reporting?

It is entirely possible that you are seeing radiator flow because this thermostat is designed to come off of its seat a little bit shortly after starting. As the water pump spools up, the pressure inside the cooling system within the engine is going to rise. The thermostat may be forced off its seat by pressure, serving not only as a theromstat but a bleed valve to regulate cooling system pressure.

My best suggestion to you would be to test the temperature sending unit. The instructions for testing will be in that Haynes manual. If you’d like to determine if you truly have an overcooling problem, then take a temperature reading at the radiator (and IR thermometer pointed at the fins will do it, or just a touch thermometer pressed between or against two fins) and compare it to the “full open” temperature of the thermostat as listed in the Haynes manual. That manual gives you the necessary information to determine if you really have a problem. Make good use of that!

My last item to bring to question would be a thermostat seal. Is there a rubber seal that goes around the thermostat? Maybe there SHOULD be one but it’s no longer there becuase this thermostat was replaced once already. Look into that. Again, the information should be in that book.

-Matt

are you COMPLETELY sure you have an OEM stat???

the reason i ask is it seems CRINGE (like your mercedes friend) your nissan may use a two step stat. one opening opens the cool engine loop, and full open circultes through the whole engine.

did you get the stat at nissan??

This problem is hard to diagnose in person! I don’t think we’ll get anywhere unless someone else has had the problem. It doesn’t help that I am not good at explaining things! ;-|

I am fairly sure the TSU is correct because the amount of heat that comes from the heater core is right in line with the gauge. In the winter - nada, spring, heat - summer- really hot (Like I wish in winter!)

I believe that it is a two stage system. I posted a link on the previous page that shows the only info I could find on the 'net about the coolant flow path. Again, no definitive test=spend $$ and fix it right or blow motor. I never liked the bitter-sweet smell of a blown head gasket…

Shall I throw in the shop towel? I was hoping that this could find someone, oh, that special someone who knew. Good-bye world! It’s been great! (OK…I thought I should finish with some melodrama :slight_smile:

I’ll check back a few more times I guess. And hey! RENAME YOUR SUBJECT WHEN YOU POST!!! My RSS feed has the same subject for each one. I just realized you can change it. Then I will actually know when there is a NEW post! Thanks everyone!!!