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

On Wed, 25 Oct 2006 00:46:32 +0000, Stephen N. rearranged some electrons to form:

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

snipped-for-privacy@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.

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...

David M wrote:

Not so. The condition as described indicates constant full coolant flow. This indicates a constant open thermostat as David M. posted.

Dave D

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.

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

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.

Stephen N.---> prolly anyway...

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

SC Tom

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...

On Wed, 25 Oct 2006 06:24:23 -0400, SC Tom rearranged some electrons to form:

That's the symptoms the OP reported.

On Wed, 25 Oct 2006 16:26:37 +0000, Stephen N. rearranged some electrons to form:

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:

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

". . . 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

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 >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...

I will be changing the thermo today and post

snipped-for-privacy@gmail.com wrote:

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 ?