OEM temp gauge readings

L

lw8000

Member
Jul 30, 2012
217
14
18
Hello all:
Not too long ago our fan clutch completely locked up and we needed a replacement. I am not entirely sure which clutch it had. We ended up putting on
an AC Delco 15-4947 after reading on it here, there was a thread by Ken Burton where he did some research and found this seemed to be the best
replacement regarding the specs of the fan and setup on the GMC, and also after reading success and failures of Hayden clutches here too.

I haven't put many miles on the coach with this new clutch but this past week we were in temps up to about 88 degrees out. (In MI, that's what we
call HOT :) ). With the old clutch in this temp range , the needle would barely pass the quarter mark on the gauge, but it would also kick in quite
often even on the highway and I'd hear the fan. Now, with the 15-4947 clutch, I noticed the gauge has gone as high as just between the quarter and
half mark while on the highway, and I never hear the fan roar like the old one. But, when getting off the highway or slowing to 55 MPH or so, the
needle settles back to the quarter mark.

I believe I've read that once it hits the half mark on the gauge, it's already overheating. Should I be concerned with the readings I'm getting?

Thanks in advance as always!
Chris

--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
> Hello all:
> Not too long ago our fan clutch completely locked up and we needed a replacement. I am not entirely sure which clutch it had. We ended up putting
> on an AC Delco 15-4947 after reading on it here, there was a thread by Ken Burton where he did some research and found this seemed to be the best
> replacement regarding the specs of the fan and setup on the GMC, and also after reading success and failures of Hayden clutches here too.
>
> I haven't put many miles on the coach with this new clutch but this past week we were in temps up to about 88 degrees out. (In MI, that's what we
> call HOT :) ). With the old clutch in this temp range , the needle would barely pass the quarter mark on the gauge, but it would also kick in quite
> often even on the highway and I'd hear the fan. Now, with the 15-4947 clutch, I noticed the gauge has gone as high as just between the quarter and
> half mark while on the highway, and I never hear the fan roar like the old one. But, when getting off the highway or slowing to 55 MPH or so, the
> needle settles back to the quarter mark.
>
> I believe I've read that once it hits the half mark on the gauge, it's already overheating. Should I be concerned with the readings I'm getting?
>
> Thanks in advance as always!
> Chris

Chris,

Assuming that the coach still has the factory temperature sensor, then yes, half scale is a worry. The other problem with the long standard
thermostatic fan clutch is that it has little or no relation to the actual coolant temperature. There is also the issue that most of those clutches
are now produced off-shore and the calibration is problematic at best.

Do you own an IR temperature gun? If not, grab one on sale for ~20$us and measure the temperature at the thermostat housing.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
One person's idea of overheated coolant, is another person's idea of proper
operating temperature. 241° degrees farenheit is DEFINITELY overheated,
where 205° might be considered "Normal". 165° - 180° might be considered
not fully warmed up by others. The correct temperature is that temperature
at which all of the air/fuel mixture possible is controlled burned with no
preignition or detonation. Just sayin'
Jim Hupy
Salem, Oregon

On Sun, Aug 16, 2020, 9:01 AM Matt Colie via Gmclist <

> > Hello all:
> > Not too long ago our fan clutch completely locked up and we needed a
> replacement. I am not entirely sure which clutch it had. We ended up
> putting
> > on an AC Delco 15-4947 after reading on it here, there was a thread by
> Ken Burton where he did some research and found this seemed to be the best
> > replacement regarding the specs of the fan and setup on the GMC, and
> also after reading success and failures of Hayden clutches here too.
> >
> > I haven't put many miles on the coach with this new clutch but this past
> week we were in temps up to about 88 degrees out. (In MI, that's what we
> > call HOT :) ). With the old clutch in this temp range , the needle
> would barely pass the quarter mark on the gauge, but it would also kick in
> quite
> > often even on the highway and I'd hear the fan. Now, with the 15-4947
> clutch, I noticed the gauge has gone as high as just between the quarter and
> > half mark while on the highway, and I never hear the fan roar like the
> old one. But, when getting off the highway or slowing to 55 MPH or so, the
> > needle settles back to the quarter mark.
> >
> > I believe I've read that once it hits the half mark on the gauge, it's
> already overheating. Should I be concerned with the readings I'm getting?
> >
> > Thanks in advance as always!
> > Chris
>
> Chris,
>
> Assuming that the coach still has the factory temperature sensor, then
> yes, half scale is a worry. The other problem with the long standard
> thermostatic fan clutch is that it has little or no relation to the actual
> coolant temperature. There is also the issue that most of those clutches
> are now produced off-shore and the calibration is problematic at best.
>
> Do you own an IR temperature gun? If not, grab one on sale for ~20$us and
> measure the temperature at the thermostat housing.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I have to ask what temperature sender your using. If you still have the st=
ock unit then you need to change it out to a NAPA TS-6469 unit. Check out =
the following information. Temperature Sender This may be old news =
for most but doesn't hurt to be told. The original temp. sender on all G=
MC Motorhomes at : 1/4 is 225 degrees, 1/2 is 250 degrees, =
3/4 is 270 degrees, and H is 280 degrees. This has caus=
ed a lot of engine damage when engine starts to overheat. Go to NAPA and ge=
t a TS-6469 sender and it will show: 1/4 180 degrees, 1/2 =
215 degrees, 3/4 240 degrees, and H 255 de=
grees. Since the standard pressure cap raises antifreeze solution boilin=
g point to 250 degrees this will be more accurate readings. I don't know wh=
y they did this but it is a serious problem. Info from GMC Motorhome News p=
ublished by Cinnabar, Dec. '95 issue. I did this and it agrees exactly with=
my VIP digital readout. If you are using the 7 blade metal fan the=
n a 2747 ish is an acceptable fan clutch. I run one of the newer 10 blade =
fiberglass fans and I found that I needed to us a 2797 ish fan clutch as th=
e 2747 doesn=E2=80=99t have enough clutch to turn it. I know this from per=
sonal experience. EXAMPLE: I had installed one of John Biwersi 10 bla=
de fiberglass units. We drove the coach out to AZ to spend the winter and =
of course the temps were cool and cold on the way out. In the spring when =
we were coming back we decided to go to Page, AZ to see the Glen Canyon Dam=
and sandstone caves and canyons. The trip to Flagstaff was uneventful as =
the temperature was in the low 70=E2=80=99s, Going north on 89 into the hi=
gh desert the temps were in the High 80=E2=80=99 to low 90=E2=80=99s and we=
were motoring along when I noticed that water temp was rising to 1/2 on th=
e gauge. Remember that I said that I use the TS-6489 temp sender. Well I =
said maybe I got a bad fan clutch, so I stopped at the next rest area that =
happened to appear about 2 miles down the road. I alway carry a spare fan =
clutch and proceeded to change it out and go on our way north on 89. About=
15 minutes later the same temp rise happened again. Once again much was in=
our favor as we entered Cameron AZ and they had an AutoZone and they had a=
2797 rated fan. 45 minutes later new fan clutch and we were on our way ag=
ain to Page, AZ. I run a 180 thermostat and it was locked in the rest of t=
he trip and I still have that fan clutch install and yes I do have a spare =
2797 type fan clutch in storage. What I learned from this experience was t=
hat the 10 blade fan requires more fan clutch engagement than the 7 blade =
fan. I gave my 2747 type units to my traveling GMC friend. He had a clutc=
h failure so he got 2 fan clutches, one to install and one for a on the roa=
d spare. J.R. Wright GMC Great Laker MHC GMCGL Tech Editor GMC E=
astern States Charter Member GMCMI 78 GMC Buskirk 29.5=E2=80=99 Stretch=
75 GMC Avion (Under Reconstruction) Michigan > On Aug 16, 2020=
, at 11:11 AM, Chris S. via Gmclist wrote: > =
> Hello all: > Not too long ago our fan clutch completely locked up an=
d we needed a replacement. I am not entirely sure which clutch it had. We =
ended up putting on > an AC Delco 15-4947 after reading on it here, there=
was a thread by Ken Burton where he did some research and found this seeme=
d to be the best > replacement regarding the specs of the fan and setup o=
n the GMC, and also after reading success and failures of Hayden clutches h=
ere too. > > I haven't put many miles on the coach with this new clutc=
h but this past week we were in temps up to about 88 degrees out. (In MI, =
that's what we > call HOT :) ). With the old clutch in this temp range ,=
the needle would barely pass the quarter mark on the gauge, but it would a=
lso kick in quite > often even on the highway and I'd hear the fan. Now,=
with the 15-4947 clutch, I noticed the gauge has gone as high as just betw=
een the quarter and > half mark while on the highway, and I never hear th=
e fan roar like the old one. But, when getting off the highway or slowing =
to 55 MPH or so, the > needle settles back to the quarter mark. > > =
I believe I've read that once it hits the half mark on the gauge, it's alre=
ady overheating. Should I be concerned with the readings I'm getting? > =
> Thanks in advance as always! > Chris > > > -- > Chris S. =
- > 77 Kingsley, 3.70 FD, mostly OEM - > S.E. Michigan > > _____=
__________________________________________ > GMCnet mailing list > Unsu=
bscribe or Change List Options: > http://list.gmcnet.org/mailman/listinfo=
/gmclist_list.gmcnet.org
 
This is great info all, thank you.

I am not 100% sure but guessing I have the OEM sending unit. Is there any way to tell for sure? Normally my gauge is right at the quarter mark, once
things have run long enough to warm up, even when starting it and letting it idle for a bit. But, if that's 225 and above "normal" I need to confirm
my sending unit and temp.

I think I will do as Matt suggested and measure the temp at the thermostat housing to see where I'm at to compare against my gauge reading and go from
there. Gotta go get a temp reader but will post back findings soon.

Thank you!
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
Just buy and install the updated temp sender. All coaches should get this update. Not expensive. With a 195 Flowcooler stat, that puts the needle at
about 1/3 when sitting on the stat throttling point.
A basic go/ no go clutch test is you should have fan roar for first 60 seconds at least, after sitting overnight. This is because the silicone fluid
redistributes by gravity partly into the working chamber. With the temperature spring cold the valve will be set to have the rotation pump the fluid
back to the non working chamber. This takes a minute or so. If no fan roar at cold start fast idle, clutch may have lost too much fluid or be
defective.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
"... I noticed the gauge has gone as high as just between the quarter and half mark while on the highway, and I never hear the fan roar like the old
one. But, when getting off the highway or slowing to 55 MPH or so, the needle settles back to the quarter mark."

This appears to be a case of a bad (clogged/scaled) radiator. The fact it cools off at lower speed to me rules out the fan as a problem, as you
normally need the fan more at LOW speed than on the highway. Of course the execrable aerodynamics of our GMC engine compartment and grill make the
fan necessary at all speeds. Of course the engine needs more cooling under load. If the radiator is clogged up or internally coated with scale or
rust, it can't transfer enough heat to the passing air. In an extreme case the air might not even be warmed enough in passage at speed to get the
cooling fan thermostat to engage. I suspect this may be your situation.

Many years a go I had a Citroen which I loved dearly, and a beautiful young lady I wished to impress. She wanted to go to the beach one hot summer's
day, so off we went. It was over 90F, and any time I went over ~50mph, my temp gauge would climb, so we drove down and back with the heat on to
prevent boiling over. Needless to say, she was not impressed. Next day, I pulled the radiator and took it to a shop to be cleaned ("rodded out").
Problem fixed, but too late for that "one that got away". ;)

Unless some other cause presents itself, (double-check the thermostat) I'd recommend removing the radiator and taking it to a radiator shop (if you
can find one these days) for disassembly and cleaning. Or you could replace it. You may be able to see down into the tanks with a borescope or
something to examine the core passages.

My 2¢,, HTH
Rick Staples
--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
 
Got it on the new sending unit and radiator. I too was wondering if the radiator is OK as I thought the same thing (temp drops quickly after slowing
down). I do have the Robertshaw/Flowkooler 195 thermostat.

Once I have a laser themometer to check this I will follow up. Thanks again!
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
> Got it on the new sending unit and radiator. I too was wondering if the radiator is OK as I thought the same thing (temp drops quickly after
> slowing down). I do have the Robertshaw/Flowkooler 195 thermostat.
>
> Once I have a laser themometer to check this I will follow up. Thanks again!

Chris,

I fear you are stuck under a preconceived misconception.....
The thermostat in the cooling system does not determine how hot the engine gets, but how cold it runs. If you think that way, thinks will go better.
195°F if the temperature when the coolant starts to go out to get cooled. When you stop putting heat into the system, it will (relatively) quickly
return to that temperature.

If you have any reservations, I could come along on a ride-around (and bring my own IR gun) and we can check things. Your sig says SE-MI like mine,
well we live in the shadow (really) of DTW and if it would quiet any nerves, I would love to help.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
> > Got it on the new sending unit and radiator. I too was wondering if the radiator is OK as I thought the same thing (temp drops quickly after
> > slowing down). I do have the Robertshaw/Flowkooler 195 thermostat.
> >
> > Once I have a laser themometer to check this I will follow up. Thanks again!
>
> Chris,
>
> I fear you are stuck under a preconceived misconception.....
> The thermostat in the cooling system does not determine how hot the engine gets, but how cold it runs. If you think that way, thinks will go
> better. 195°F if the temperature when the coolant starts to go out to get cooled. When you stop putting heat into the system, it will
> (relatively) quickly return to that temperature.
>
> If you have any reservations, I could come along on a ride-around (and bring my own IR gun) and we can check things. Your sig says SE-MI like
> mine, well we live in the shadow (really) of DTW and if it would quiet any nerves, I would love to help.
>
> Matt

Thanks Matt! Yes I do understand that and was referencing that we have the 195 thermostat compared to the other replies. This should be simple
enough but if I run in to any dilemma I can reach out. I've been meaning to pick up one of these laser temp readers for a long time, now I have an
excuse to get one :) Thank you for the offer!

Take care,
Chris
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
Finally got a laser temp gun. Warmed up the engine for about 15 minutes to let it get nice and hot. Opened the hatch while engine running, and while
the gauge is on the quarter mark, and I measured the temp at the outlet at about 193 degrees. Next step will be to get the Napa sending unit and put
that on to see where that one lies.
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
Just dropped in the Napa sending unit today. In taking temp readings now, the Napa unit is spot on with what J.R. posted. I ran the engine and let
it idle up to normal temp for a good 20 minutes. The highest the gauge showed was now just slightly above halfway between the quarter and half marks.
My readings right at the sending unit on the manifold was about 201-202 degrees.

Now that it's a little more accurate I will have to watch the gauge very closely to see if it's running too hot. Based on the feedback, if this gauge
now gets up around the 3/4 mark, I may be in trouble (~240 degrees)?

Thanks again!
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
 
Rule of thumb, what the gage shows do not go much more than 1/8 more than
normal.
Sometime one can try to go 1/4, but risky.

On Wed, Sep 16, 2020 at 4:36 PM Chris S. via Gmclist <

> Just dropped in the Napa sending unit today. In taking temp readings now,
> the Napa unit is spot on with what J.R. posted. I ran the engine and let
> it idle up to normal temp for a good 20 minutes. The highest the gauge
> showed was now just slightly above halfway between the quarter and half
> marks.
> My readings right at the sending unit on the manifold was about 201-202
> degrees.
>
> Now that it's a little more accurate I will have to watch the gauge very
> closely to see if it's running too hot. Based on the feedback, if this
> gauge
> now gets up around the 3/4 mark, I may be in trouble (~240 degrees)?
>
> Thanks again!
> --
> Chris S. -
> 77 Kingsley, 3.70 FD, mostly OEM -
> S.E. Michigan
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
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