Patrol RB30 thermal vacuum valve(TVV) vacuum test

[dom14]

Hi Guys,
I've been wondering whether there's an issue with the thermal vacuum valve(picture below) & whether it is not doing it's job right.
So, I decided to do a vacuum test again with the tester.
Basically, the TVV opens the vacuum passage to the distributor vacuum advance diaphragm once the engine is warmed up to
a certain level.
Since it's only been showing around 10 In-Hg of vacuum when I tested it last time, I've been wondering whether there's an issue
with the TVV.

Here I did the test in a different way this time and uploaded a very short video as well.

https://www.youtube.com/watch?v=QHC9dWJPlsU&feature=youtu.be

I pulled the vacuum line from the distributor vacuum advance diaphragm and connected it to the vacuum tester.
Then I started the engine(cold start) and checked vacuum. There's no vacuum showing which is ok, because the vacuum passage
opens once the engine is warmed up enough. That's the purpose of the TVV.
But, I was hearing this faint hissing noise and assumed it's coming from the top of the TVV(see the picture and the video).
I covered the top of the TVV with the finger and vacuum tester suddenly shows vacuum.
So, it's confirmed the 'vacuum leak' and the hissing noise was coming from the TVV.

Now I'm wondering whether the TVV is actually faulty.
Because I only connected the tester to the top line of the TVV(where it goes to the distributor vacuum advance diaphragm).
If I connected the vacuum tester to the bottom line, there's no vacuum showing in the tester.
This puzzles me.

There's no vacuum in the bottom vacuum line of the TVV when I tested it engine cold running.
so Where did the vacuum that showed on the TVV top vacuum line came from in the first place when I blocked the top hole of the TVV) ??!!!

When I cover the top of the TVV, the vacuum suddenly shows up on the tester. So, this vacuum must have come from the bottom line.
But, it only get activated when I cover the top of the TVV. This is all puzzling.

I am having serious trouble understanding this result.

I've also attached the vacuum diagram of my RB30 Patrol.

Can you guys please help me? There's no stock vacuum diagram for RB30 Patrol for me to have a look and compare.
So, my diagram below is the only one I have for reference.
I'm sure an experienced bloke out there can point me in the right direction.

Thanks guys.

[mudnut]

I just got back from a
long highway run and
there is no change to the revs if
I place my finger on top
of the valve. This indicates
there may be a problem
with yours. I will test it
tomorrow when the engine is
cold.

[dom14]

Thanx mate. I couldn't notice much of the RPM change, but the vacuum jump from zero to 10 in-Hg is obvious.
Since the top of the TVV shouldn't apparently have any connection to the interior vacuum passage of the TVV, this result
does look strange to me. Very little literature can be found about the RB30 Patrol TVV operation.
If you don't have a vacuum tester, do the same as mine. But, instead of the tester, put your finger at the end of the vacuum line to the distributor vacuum advance diaphragm. If there's any vacuum, you should be able to feel it.
Just make sure not to get the hand caught up too close to the fan. I always wear gloves when working on running engine to save some skin. :D

[mudnut]

Dom, the valve does vent to atmosphere
while the engine is cold.

[dom14]

Dom, the valve does vent to atmosphere
while the engine is cold.

Hi Craig,

Yes, I suspected that.
I needed a confirmation as I don't have much understanding of the internals of the Thermal Vacuum Valve.

Valve is producing 10 In-Hg, instead of around 20. So, Is that a problem with the valve?!! I wonder.
In my previous thread i mentioned that the thermal valve vacuum lines were swapped when I checked it with the Haynes manual indicated setting.
I reckon it was done purposely, rather than accidentally to get an advantage on LPG.

BTW, do you know a dizzy rebuilding expert in Melbourne or surrounding areas?

Thanks mate.

[mudnut]

It is quit a bad design,
having an intake vent
under the bonnet of
a 4wd.
I am happy with
the RB30 performance,
But if I had my choice
over again, I would have
bought a TB42.
The RB30 gearbox is, IMHO,
too light for 4wd and
towing duty.

The RB30 has a timing belt
that needs changing out
every 100000ks.
And is open to getting
mud, water and dust
contamination.
As we've just discovered,
the TVV is open to
atmosphere, faces upwards
and can collect moisture and
dust.

If you get another valve,
I would be interested to see
if there is a filter fitted to it.

[dom14]

Dom, the valve does vent to atmosphere
while the engine is cold.

I had to edit my previous post. Somehow, I read DOES as DOES NOT in your post.

I'm wondering mate, what is your opinion?

Can it be right?

Either I have a very little understanding of the TVV's operation or TVV is faulty.

Venting of the TVV means less vacuum to the distributor vacuum advance diaphragm.
The same line is connected to the carby throttle body as well.

I reckon I experiment with blocking the top of the TVV with either sticky tape or silicon and see how it goes??!!

[mudnut]

When my unit is hot
there is no hissing
sound or vacuum
on top of the valve.
Maybe there is a bit
of crud stuck in the
valve of yours.

[dom14]

It is quit a bad design,
having an intake vent
under the bonnet of
a 4wd.
I am happy with
the RB30 performance,
But if I had my choice
over again, I would have
bought a TB42.
The RB30 gearbox is, IMHO,
too light for 4wd and
towing duty.

The RB30 has a timing belt
that needs changing out
every 100000ks.
And is open to getting
mud, water and dust
contamination.
As we've just discovered,
the TVV is open to
atmosphere, faces upwards
and can collect moisture and
dust.

If you get another valve,
I would be interested to see
if there is a filter fitted to it.

I think I start with the blocking of the supposed vent with sticky tape or silicon, and see how it goes.
I reckon a brand new TVV won't be cheap, 'cos I don't think there're any aftermarket ones of them.
It will be the original Nissan one.

My timing belt is due for a change as well.

How does the mud, water, dust, etc get into the timing belt compartment?!

I'm thinking TVV may not supposed to be open to the atmosphere when cold?!!
What do you reckon?
What if it's doing that 'cos it's gone faulty over years of use?

I agree with you 100%. RB30 gearbox is not a bull horse. It's certainly not meant for heavy towing.
I tow a van with mine. But, it's a fairly light 11 footer.
With turbo upgrade, blokes do some heavy off roading in the bush, but I reckon it does wear out or go bang at times.

The reason I went for the RB30 'cos of the fuel economy and the ability to cruise long distances on not so demanding terrain.
And not to mention, well looked after RB30 motor is very reliable. gasket failure is the common thing, which is also a problem with
the TB42s.
TB42 is better with EFI I reckon. If I go for a TB42, I would seek for an EFI one. Carby ones are more trouble than the RB30 and real fuel guzzlers.

[mudnut]

There is some small holes
in the top of the timing cover
and also there is no seal
between the harmonic balancer
and the cover.

I would really consider
the waterless coolant
except that you have
to pull the radiator out
to get to the timing belt.

If you do the belt
yourself it is easy to use a
mirror to get the bottom
timing mark aligned properly.
I had to use the starter to
crack the harmonic balancer
bolt.

[dom14]

Ok, cool.
I'll see whether I can find a way to create a proper seal to prevent the gunk from getting into the timing belt.

What waterless coolant can you use?
Why do you recommend waterless coolant?

I have 3/4 inch rattle gun, but that won't help as I won't be able to fit it in there even with the radiator off.

[dom14]

Not trying to be too cheap,
but wondering whether I can take the water pump out during the timing belt replacement job and examine and sort of recondition it. ??!!
The idea is to extend the water pump life and prevent a sudden failure.

[mudnut]

I have sealed the top
of the cover, drilled a
small hole near the top
and fitted a small nipple
so there in anticipation
of pressurising the cover
and dissy with 1-2 psi
in the future.

[mudnut]

Not trying to be too cheap,
but wondering whether I can take the water pump out during the timing belt replacement job and examine and sort of recondition it. ??!!
The idea is to extend the water pump life and prevent a sudden failure.

Funny, you say that because my
water pump spat the dummy
only 5000 ks after I changed out
the belt and did the head gasket.

[dom14]

I did the head around 40k ago. The water pump is still going.
I should've done the timing belt during that time, but didn't have enough time(or knowledge to know it's vital)
I reckon it's not going to go forever. I thought about dealing with the water pump while I'm doing the
timing belt job. Replacing is obviously the best option.
But, I like the idea of recycling them
1)It's usually the seal that fails which in turn can affect the bearing as well(or vice versa). But, both are replaceable if the parts can be found.
2)New pump is $150 or more. Big difference, comparing the VL commodore one which is $40 mark.

I like the idea of rebuilding the water pump, if it's doable, parts availability wise.

[dom14]

I have sealed the top
of the cover, drilled a
small hole near the top
and fitted a small nipple
so there in anticipation
of pressurising the cover
and dissy with 1-2 psi
in the future.

Do you reckon that might have something to do with the water pump failure rather than the timing belt job?!!

[mudnut]

Nah, as the nipple is still open to
atmosphere. The head
gasket failed as a result
of the mechanic not
setting the timing right.
Another Old School mechanic
explained that silent detonation
caused higher
than normal cylinder temps
which split the fire rings in
two cylinders.
The head was planed, the
gasket replaced and the radiator
was repaired. This left the old
water pump as the weak link
and it failed.

[dom14]

Good point you just brought up there about the silent detonation

Do you know how to detect the silent detonation in motors like the RB30?!

I'm guessing examining the spark plugs closely?

What else can we do?

[mudnut]

The first clue the
good mechanic noticed
was the colour of
the exhaust manifold.
I had no idea what
colour it should be,
but he said it was running
hot. My mate who
runs a dynotune business
reset the timing after
all the work was done.
He had to retard it quite a bit
to get peak power output.

[dom14]

Hi Craig,
Where is your mate located?
I need to get mine dynoed once I finish all the work soon.
Thanx

[mudnut]

Not far from
my place. He actually
specialised in racing
engines. The RB30
was quite a common
engine used down here.
He now has a clean
room and some machines
to rebuild heads and such.
You should be able to
find a good, highly
recommended dynotuner
near you.

[dom14]

I previously thought TVV function is mostly for the EGR. But, studying my own diagram indicates since two vacuum lines go to the TVV from EGR+charcoal canister & distributor vacuum diaphragm, then it can't be just about EGR & charcoal canister. The dizzy vacuum diaphragm must be involved with the mechanism. I am not 100% certain whether the top vacuum line that comes out of the TVV goes into the dizzy(It T's down the line and one goes to the dizzy vacuum & other to the carby throttle body). Is that the way yours connected? I've been thinking it might have been incorrect in mine. May be the dizzy line goes to the bottom line of the TVV. This matters 'cos the TVV vents the vacuum to the air when the engine's cold running, effectively reducing the vacuum to either one of the line. I'm thinking it can't be the dizzy line 'cos that's purely controlled by the engine rpm(whether it'd idling or revving). I don't think dizzy vacuum line function has anything to do with the engine temperature(Correct me if I'm wrong about that).

I'm thinking TVV may be about equalizing the vacuum between dizzy vacuum diaphragm, EGR & charcoal canister once the engine's fully warmed up. . May be it's there to apply only partial vacuum to the EGR & charcoal canister(rather than the dizzy vacuum diaphragm) when the engine's cold, but equalize the vacuum between all three(dizzy vacuum, charcoal canister & EGR) once the engine's fully warmed up. Only issue with that argument is that then there's no need for the dizzy vacuum line to go into the TVV(assuming there in no need to thermally control the vacuum to the dizzy vacuum diaphragm). No argument Nissan engineers got it right and it is an emission control thing(either partially or fully 'cos it's connected to EGR and charcoal canister). The thing I'm confused about is TVV's possible function with the dizzy vacuum advance diaphragm. Since the dizzy vacuum advance line is connected to the TVV, it must be performing some function and it's not clear to me what it is. Whatever it is, it is connected with carby throttle body vacuum lines as well, 'cos two lines come out the TVV connects to two separate vacuum lines on the carby throttle body, obviously for a good reason that has something to do with the carby throttle body internal vacuum function.

[dom14]

There is a discussion about the TVV below about a different car, but somewhat relevant about the function and the trickiness of the TVV.

https://www.corvetteforum.com/forums/c3-tech-performance/2408414-what-is-the-function-of-the-thermal-vacuum-switch.html

[mudnut]

I have only skimmed the surface with regards to the operation and function of the valve, Dom. I found the top was loose and that it screwed off. I found the valve was full of crud. I cleaned it and added a line on the inlet to run up to the diff breathers and fitted a cheap fuel filter on the end. All is good so I am leaving well alone.

[dom14]

I have only skimmed the surface with regards to the operation and function of the valve, Dom. I found the top was loose and that it screwed off. I found the valve was full of crud. I cleaned it and added a line on the inlet to run up to the diff breathers and fitted a cheap fuel filter on the end. All is good so I am leaving well alone.

Thanx mate. I remember you advised me about cleaning it above. Being a slacker at that time I didn't screw it off. I sprayed a bit of WD40 & then hissed some pressurized gas at it. I'll do a proper cleaning job soon.

Craig,
Can you please confirm with me whether the top vacuum line out of the TVV goes to the dizzy vacuum advance diaphragm(via the T down the line) or to the EGR+charcoal canister(via a T down the line again)?
Thanx mate

[mudnut]

I'll try and remember to have a look tomorrow, Dom.

[dom14]

I'll try and remember to have a look tomorrow, Dom.

Any chances, yet? :)

[mudnut]

I have just got back in to have lunch. As I said, my Patrol is running well so I am not gunna change anything. The bottom hose runs to a T piece off which runs the vac advance and a line to the bottom D/S of the carby.

The top hose is to a T off which one line goes to the canister The other runs to another T which goes to just in front of the first line (mentioned above) at the base of the carby. The other branch runs to the egr valves.

The two hoses on the TVV may have been swapped before I got the car, or inadvertantly since. I have no idea.

[dom14]

I have just got back in to have lunch. As I said, my Patrol is running well so I am not gunna change anything. The bottom hose runs to a T piece off which runs the vac advance and a line to the bottom D/S of the carby.

The top hose is to a T off which one line goes to the canister The other runs to another T which goes to just in front of the first line (mentioned above) at the base of the carby. The other branch runs to the egr valves.

The two hoses on the TVV may have been swapped before I got the car, or inadvertantly since. I have no idea.

Thanx mate. No, I didn't ask you to fiddle with it by swapping them. I just wanted to know the way yours is connected.
It's obviously different from mine as well as the diagram I produced two years ago.
As you said, yours might have been swapped or it might have been mine.
I obviously need to acquire more reports of our fellow RB30 Patrol owners(in stock format) before I come to a conclusion about this.
ATM, I'm assuming there is a difference between the top vacuum port and the bottom vacuum port of the TVV.
If there is NO difference, then of course it won't matter which one is plugged into which.
I'll confirm this once for all sometime soon.
I'll be opening a thread to gather information about this soon.

Cheers
Dom

P.S. For starters, I'm gonna swap the vacuum hoses to be consistent with your setup and see whether that makes any difference.
Before that, I obviously need to clean the TVV properly as you indicated.

[dom14]

Have a read of the description that follow the below TVV listing for another car.

https://www.ecklers.com/nova/nova-ac-delco-thermal-vacuum-valve-1977-1979.html

" Engine running rough? Is your check engine light on? It could be a failed Thermal Vaccum Valve on your 1977-1979 Nova. This could be the cause of your problem, because this valve removes the vacuum applied to the distributor advance and disables the EGR valve while the engine is warming up, it's an intentional air leak in those circuits when the engine is cold. If it's broken off, or if one of the ears is broken off it becomes a vacuum leak which will disable both all the time, resulting in poor performance and a fault code "

And apparent issue with mine is the TVV keeps leaking air into the atmosphere even after engine's warmed up, indicating it may be faulty.
I've blocked the vacuum lines that go to the TVV anyway, so it shouldn't be an issue with mine atm, ideally.

[dom14]

I think this is how the TVV function is tested.

To check whether the TVV is working properly, when the engine's cold running, put the tip of your finger on the air vent on top of the TVV. You should be able to feel the vacuum/air hissing into the TVV on your finger tip. Then allow the engine to fully warm up and do the same. This time there shouldn't be any air venting/hissing/vacuum leak. If it's still venting after warm up, then the TVV should be faulty. Either cleaning it or replacing it may be necessary. You can unscrew the top bit carefully and clean the internals carefully with WD40 and a tooth brush.

[mudnut]

Just take it easy while the engine is cold.

[dom14]

Just take it easy while the engine is cold.

Yeah, and I reckon TVV function probably not an issue with mine once I blocked both vacuum lines that go to it, 'cos I removed EGR system in mine ages ago. But, just to be safe, I'll either fix the TVV or replace it and connect the vacuum lines the way it should be.
The only thing that I still don't understand is the TVV function relation to the charcoal canister, 'cos the bottom line off the TVV goes to the charcoal canister & the vacuum port on the carby throttle body. So, I reckon, the TVV function in RB30 carby engine is bit more complicated than the TVV and the explanation I quoted in the above link. So, I still have some understanding to get to with the RB30 TVV function. Looks like I'm pretty close to it. :)