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Car Forum / Ford / Ford Trucks / October 2006

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98 Mazda B4000 (4.0L) Upper Radiator Hose HOT Lower COLD ??

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ndccpf1@gmail.com - 25 Oct 2006 01:08 GMT
Upper (left) big hose is HOT and the lower (bottom Right) hose and
radiator is COLD after driving for 1/2 hour. Temp gauge always on COLD.
My water pump ?
Stephen N. - 25 Oct 2006 01:46 GMT
Your thermostat is probably stuck shut.

> Upper (left) big hose is HOT and the lower (bottom Right) hose and
> radiator is COLD after driving for 1/2 hour. Temp gauge always on COLD.
> My water pump ?
David M - 25 Oct 2006 02:24 GMT
> Your thermostat is probably stuck shut.

If the engine is not heating up, the thermostat is stuck OPEN.

>> Upper (left) big hose is HOT and the lower (bottom Right) hose and
>> radiator is COLD after driving for 1/2 hour. Temp gauge always on COLD.
>> My water pump ?

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David M  (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14  has been up 27 days 9:25

Stephen N. - 25 Oct 2006 04:44 GMT
It sounds like the engine is heating up and the heated coolant is getting
TO the radiator but not THROUGH it.  Generally though, the coolant flows
from the top hose of the rad through the Tstat and back into the rad
through the bottom hose.  So I find it odd that the top hose is hot and
the bottom is cold.

If there is coolant in the system, the water pump may not be
functioning.  In any case it really seems like there is not proper
coolant flow.  There aren't a lot of reasons that would cause that.

Stephen N.---> more than enough though, it seems...

>>Your thermostat is probably stuck shut.
>
[quoted text clipped - 3 lines]
>>>radiator is COLD after driving for 1/2 hour. Temp gauge always on COLD.
>>>My water pump ?
SC Tom - 25 Oct 2006 11:24 GMT
> It sounds like the engine is heating up and the heated coolant is getting
> TO the radiator but not THROUGH it.  Generally though, the coolant flows
[quoted text clipped - 7 lines]
>
> Stephen N.---> more than enough though, it seems...

Doesn't coolant flow from the bottom hose TO the engine, then through the
thermostat back into the radiator? If the t'stat is stuck open, the temp
will be higher on the top hose and cooler on the bottom because the water
doesn't have enough time in the engine to get up to temp, then looses what
heat it did gain traveling down through the radiator, as is the case here, I
believe.

SC Tom
Stephen N. - 25 Oct 2006 17:26 GMT
>>It sounds like the engine is heating up and the heated coolant is getting
>>TO the radiator but not THROUGH it.  Generally though, the coolant flows
[quoted text clipped - 14 lines]
> heat it did gain traveling down through the radiator, as is the case here, I
> believe.

Depending on the vehicle, it is sometimes possible to see the direction
of coolant flow into rad through the top hose.

Here's a simple diagram of a coolant schematic.  I couldn't vouch for
the system in question but I think most are similar to this one.

http://ep0niks.ctech.ca/vw/eva2/GE02/ch1.html

Stephen N.---> prolly anyway...
SC Tom - 26 Oct 2006 02:06 GMT
>>>It sounds like the engine is heating up and the heated coolant is getting
>>>TO the radiator but not THROUGH it.  Generally though, the coolant flows
[quoted text clipped - 24 lines]
>
> Stephen N.---> prolly anyway...

I guess it is vehicle dependant. This was the one I was thinking of:

http://www.binderbulletin.org/faq/3.htm#3

SC Tom
Stephen N. - 26 Oct 2006 02:34 GMT
> "Stephen N." <Steelystephen@coldmail.com> wrote in message
>>Here's a simple diagram of a coolant schematic.  I couldn't vouch for the
[quoted text clipped - 5 lines]
>
> http://www.binderbulletin.org/faq/3.htm#3

Well, that seems quite opposite doesn't it?  Coulda bin one of those
stupid arguments between two lesser fellas eh?  lol...

Stephen N.---> 'course your site's prolly rong...
David M - 26 Oct 2006 09:53 GMT
>>>It sounds like the engine is heating up and the heated coolant is getting
>>>TO the radiator but not THROUGH it.  Generally though, the coolant flows
[quoted text clipped - 24 lines]
>
> Stephen N.---> prolly anyway...

In your link, it is not possible to tell which hose is the
top and which is the bottom.  

If you read a little further down, your link says:
http://ep0niks.ctech.ca/vw/eva2/GE02/ch4.2.html

A thermostat stuck open will cause the engine to warm up slowly and run
below normal temperature at highway speed.

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David M  (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14  has been up 28 days 16:50

Stephen N. - 26 Oct 2006 17:42 GMT
>>Depending on the vehicle, it is sometimes possible to see the direction
>>of coolant flow into rad through the top hose.
[quoted text clipped - 14 lines]
> A thermostat stuck open will cause the engine to warm up slowly and run
> below normal temperature at highway speed.

It's true the hoses are not marked as top and bottom but in my limited
experience I've usually found the thermostat to be on top of the engine,
connected to the top of the rad with a fat hose.  This was also true of
Mitsubishi 4cyls common in Chrysler cars and minivans.

I have to admit this is mostly on older V8's and inline 6's and I
haven't had to have a good look at the coolant system in my truck.

But back to the OP's observation.  He says:

>Upper (left) big hose is HOT and the lower (bottom Right) hose and
>radiator is COLD after driving for 1/2 hour. Temp gauge always on COLD.
>My water pump ?

If the top hose is hot it can only have been heated by the engine.
If the rad is cold then hot coolant is not flowing through it.
This suggests there is little or no circulation and that points to:
- a thermostat that is stuck closed
- a water pump that is not circulating coolant, or
- inadequate quantity of coolant.

Of those, only a non-operational temp sensor or lack of coolant would
cause a cold temp reading.

I can't think of what other causes there may be.

Stephen N.---> but I never said I had all the answers...
David M - 26 Oct 2006 09:46 GMT
> Doesn't coolant flow from the bottom hose TO the engine, then through the
> thermostat back into the radiator? If the t'stat is stuck open, the temp
> will be higher on the top hose and cooler on the bottom

That's the symptoms the OP reported.

Signature

David M  (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14  has been up 28 days 16:47

SC Tom - 26 Oct 2006 11:20 GMT
>> Doesn't coolant flow from the bottom hose TO the engine, then through the
>> thermostat back into the radiator? If the t'stat is stuck open, the temp
>> will be higher on the top hose and cooler on the bottom
>
> That's the symptoms the OP reported.

". . . down through the radiator, as is the case here, I
believe."

That's what I was alluding to at the end of my reply.

Have a good one!

SC Tom
Rodan - 25 Oct 2006 02:39 GMT
ndccpf1@gmail.com wrote:         98 Mazda B4000 4.0L

Upper (left) big hose is HOT and the lower (bottom Right)
hose and radiator is COLD after driving for 1/2 hour. Temp
gauge always on COLD.   My water pump ?
______________________________________________

There may be some information missing.    The condition
described indicates there is no coolant flow.   The engine
would overheat and the radiator would boil over if the car
was driven for 1/2 hour without coolant flow.

Is it possible that those hot and cold hoses are actually
the heater hoses and not the radiator hoses?

Rodan.
Dave and Trudy - 25 Oct 2006 08:30 GMT
> ndccpf1@gmail.com wrote:         98 Mazda B4000 4.0L
>
[quoted text clipped - 12 lines]
>
> Rodan.
Not so. The condition as described indicates constant full coolant flow.
This indicates a constant open thermostat as David M. posted.

Dave D
Joe S. - 25 Oct 2006 09:21 GMT
> Upper (left) big hose is HOT and the lower (bottom Right) hose and
> radiator is COLD after driving for 1/2 hour. Temp gauge always on COLD.
> My water pump ?

I can't speak for the temp of the hoses -- but -- my 97 B4000 temp gauge
stayed on cold, barely moving off the C.  Problem was the thermostat --  
replaced thermostat and gasket and it's humming along.
ndccpf1@gmail.com - 28 Oct 2006 11:18 GMT
I will be changing the thermo today and post

> Upper (left) big hose is HOT and the lower (bottom Right) hose and
> radiator is COLD after driving for 1/2 hour. Temp gauge always on COLD.
> My water pump ?
ndccpf1@gmail.com - 29 Oct 2006 11:21 GMT
Replaced thermo yestereday..temp guage now working, interior heat
EXCELLENT now..

only thing now I see is that the temperature knob when put to
COLD.....continues to send HOT air inside the truck, I looked inside
the engine are area to see what looks like a vacumm controlled vavle
attached to firewall hoses. I removed the heater control panel and see
that the temperature dial is not directly vacumm controlled but appears
to be a rheostat.

Ideas ?
 
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