Intermittent cooling problem in a Dodge 2.5

What could cause an intermittent cooling problem in a Dodge 2.5 ('94 Caravan)?

This car has eaten several heads, but I haven't been around to watch the temp
gauge as they were destroyed. Tuesday night I got my chance. The car had
been on for about 2 miles of slow (30 mph) driving. About the point where
the thermostat would open and clamp the temp gauge (about 1/3 scale), it just
kept climbing. It climbed fast, and in the 1/2 mile or so it took to find
a safe place to get off of the road, it had gone full scale and triggered the
"check gauges, dummy" light and chime. The head felt hot, but not too hot
(not as hot as summer driving with things working correctly). The top
radiator hose was cool, and when I opened the cap (cool to the touch) water
sprayed out, but not hot water. None was boiling out until then.

The next day, I went back and visually inspected everything. Started it up,
and it warmed up as normal. Drove it 10 miles home, gauge came up to normal
position. At home the top hose was hot. Seemed fine.


I'd say it was a thermostat, or the temp sensor EXCEPT that the car has
been hard on heads, and the thermostat is only a month or so old. It was
installed, along with a new head, when the car overheated in August. After
replacing the head I idled the car quite a bit, with the heat all the way on.
I properly filled and burped the cooling system. Had "OK" heat. I ran it
for a month or so with the heat off mainly, occasionally turned it full on
to check that I was blowing hot air (no bubble in heater core). The night
it acted up was actually the first cool night in awhile, and the first time
I had the heat about halfway on. A google search previously had previously
revealed someone claiming that a blocked heater core caused his 2.5 to over-
heat. (So when I started it and drove it home yesterday I kept the heat all
the way off). Looking at the way it is plumbed up, only a small part of the
cooling water would go through the heat core -- can this really be a problem?

Also, when it overheated in August, I was up in the mountains of Colorado
(probably 7-8000 feet). I replaced the thermostat then, and boiled both the
old an the new T-stat in a pan of water first. Both opened, but only about
3/8ths of an inch. I realized that boiling water isn't that hot at altitude,
and put the new one in.


So, either my water pump isn't pumping, or my thermostat isn't opening
SOMETIMES. I don't want to just replace the T-stat and ignore it, since
next time somebody else might be driving and not notice the gauge creeping
up (the head seems fine now, I think I got off the road in time).

So, either my water pump isn't pumping, or my thermostat isn't opening
SOMETIMES. I don't want to just replace the T-stat and ignore it, since
next time somebody else might be driving and not notice the gauge creeping
up (the head seems fine now, I think I got off the road in time).

I guess I could pull the water pump, and take it apart. The impeller could
be loose on the shaft? What else could cause an intermittent problem like
this? I'll isolate the heater core and flush it out, but the coolant looked
clean (1 year old) when it blew up in August, and I flushed it and it looked
fine in September after I put it back together.

I'd really like to see the cause of the problem (vs. replace a couple of
parts) so that I can convince myself that it's really fixed this time.

Any ideas?


Thanks,


Bob

On 14 Oct 2004 06:36:44 -0700, (Bob Fourney) wrote:

>What could cause an intermittent cooling problem in a Dodge 2.5 ('94 Caravan)?
<snip>
>I'd really like to see the cause of the problem (vs. replace a couple of
>parts) so that I can convince myself that it's really fixed this time.
>
>Any ideas?
>
>
>Thanks,
>
>
>Bob

My money's on the water pump, since you say that when you popped the
radiator cap what came out was not hot. That tells me the water is not
circulating through the radiator.

I ain't no mechanic, but that's how it looks to me.
Mike

Mike Patterson
Please remove the spamtrap to email me.
"I always wanted to be somebody...I should have been more specific..." - Lily Tomlin

On 14 Oct 2004 06:36:44 -0700, (Bob Fourney) wrote:

>What could cause an intermittent cooling problem in a Dodge 2.5 ('94 Caravan)?
<snip>
>I'd really like to see the cause of the problem (vs. replace a couple of
>parts) so that I can convince myself that it's really fixed this time.
>
>Any ideas?
>
>
>Thanks,
>
>
>Bob

My money's on the water pump, since you say that when you popped the
radiator cap what came out was not hot. That tells me the water is not
circulating through the radiator.

I ain't no mechanic, but that's how it looks to me.
Mike

Mike Patterson
Please remove the spamtrap to email me.
"I always wanted to be somebody...I should have been more specific..." - Lily Tomlin

>
> This car has eaten several heads, but I haven't been around to watch the
temp
> gauge as they were destroyed. Tuesday night I got my chance. The car had
> been on for about 2 miles of slow (30 mph) driving. About the point where
> the thermostat would open and clamp the temp gauge (about 1/3 scale), it
just
> kept climbing. It climbed fast, and in the 1/2 mile or so it took to find
> a safe place to get off of the road, it had gone full scale and triggered
the
> "check gauges, dummy" light and chime. The head felt hot, but not too hot
> (not as hot as summer driving with things working correctly). The top
> radiator hose was cool, and when I opened the cap (cool to the touch)
water
> sprayed out, but not hot water. None was boiling out until then.
>
> The next day, I went back and visually inspected everything. Started it
up,
> and it warmed up as normal. Drove it 10 miles home, gauge came up to
normal
> position. At home the top hose was hot. Seemed fine.
>
>
> I'd say it was a thermostat, or the temp sensor EXCEPT that the car has
> been hard on heads, and the thermostat is only a month or so old. It was
> installed, along with a new head, when the car overheated in August.
After
> replacing the head I idled the car quite a bit, with the heat all the way
on.
> I properly filled and burped the cooling system. Had "OK" heat. I ran it
> for a month or so with the heat off mainly, occasionally turned it full
on
> to check that I was blowing hot air (no bubble in heater core). The night
> it acted up was actually the first cool night in awhile, and the first
time
> I had the heat about halfway on. A google search previously had
previously
> revealed someone claiming that a blocked heater core caused his 2.5 to
over-
> heat. (So when I started it and drove it home yesterday I kept the heat
all
> the way off). Looking at the way it is plumbed up, only a small part of
the
> cooling water would go through the heat core -- can this really be a
problem?
>
> Also, when it overheated in August, I was up in the mountains of Colorado
> (probably 7-8000 feet). I replaced the thermostat then, and boiled both
the
> old an the new T-stat in a pan of water first. Both opened, but only
about
> 3/8ths of an inch. I realized that boiling water isn't that hot at
altitude,
> and put the new one in.
>
>
> So, either my water pump isn't pumping, or my thermostat isn't opening
> SOMETIMES. I don't want to just replace the T-stat and ignore it, since
> next time somebody else might be driving and not notice the gauge creeping
> up (the head seems fine now, I think I got off the road in time).
>
> So, either my water pump isn't pumping, or my thermostat isn't opening
> SOMETIMES. I don't want to just replace the T-stat and ignore it, since
> next time somebody else might be driving and not notice the gauge creeping
> up (the head seems fine now, I think I got off the road in time).
>
> I guess I could pull the water pump, and take it apart. The impeller
could
> be loose on the shaft? What else could cause an intermittent problem like
> this? I'll isolate the heater core and flush it out, but the coolant
looked
> clean (1 year old) when it blew up in August, and I flushed it and it
looked
> fine in September after I put it back together.
>
> I'd really like to see the cause of the problem (vs. replace a couple of
> parts) so that I can convince myself that it's really fixed this time.
>
> Any ideas?

I'd go for the radiator or the electric fan (if it is indeed an electric
one) that cools the radiator. If the fan is not turning on (or is
intermittently not working when needed) that will cause an overheat. Also
if the radiator is clogging up that will reduce the cooling capacity also
causing the symptoms you described.

>
> This car has eaten several heads, but I haven't been around to watch the
temp
> gauge as they were destroyed. Tuesday night I got my chance. The car had
> been on for about 2 miles of slow (30 mph) driving. About the point where
> the thermostat would open and clamp the temp gauge (about 1/3 scale), it
just
> kept climbing. It climbed fast, and in the 1/2 mile or so it took to find
> a safe place to get off of the road, it had gone full scale and triggered
the
> "check gauges, dummy" light and chime. The head felt hot, but not too hot
> (not as hot as summer driving with things working correctly). The top
> radiator hose was cool, and when I opened the cap (cool to the touch)
water
> sprayed out, but not hot water. None was boiling out until then.
>
> The next day, I went back and visually inspected everything. Started it
up,
> and it warmed up as normal. Drove it 10 miles home, gauge came up to
normal
> position. At home the top hose was hot. Seemed fine.
>
>
> I'd say it was a thermostat, or the temp sensor EXCEPT that the car has
> been hard on heads, and the thermostat is only a month or so old. It was
> installed, along with a new head, when the car overheated in August.
After
> replacing the head I idled the car quite a bit, with the heat all the way
on.
> I properly filled and burped the cooling system. Had "OK" heat. I ran it
> for a month or so with the heat off mainly, occasionally turned it full
on
> to check that I was blowing hot air (no bubble in heater core). The night
> it acted up was actually the first cool night in awhile, and the first
time
> I had the heat about halfway on. A google search previously had
previously
> revealed someone claiming that a blocked heater core caused his 2.5 to
over-
> heat. (So when I started it and drove it home yesterday I kept the heat
all
> the way off). Looking at the way it is plumbed up, only a small part of
the
> cooling water would go through the heat core -- can this really be a
problem?
>
> Also, when it overheated in August, I was up in the mountains of Colorado
> (probably 7-8000 feet). I replaced the thermostat then, and boiled both
the
> old an the new T-stat in a pan of water first. Both opened, but only
about
> 3/8ths of an inch. I realized that boiling water isn't that hot at
altitude,
> and put the new one in.
>
>
> So, either my water pump isn't pumping, or my thermostat isn't opening
> SOMETIMES. I don't want to just replace the T-stat and ignore it, since
> next time somebody else might be driving and not notice the gauge creeping
> up (the head seems fine now, I think I got off the road in time).
>
> So, either my water pump isn't pumping, or my thermostat isn't opening
> SOMETIMES. I don't want to just replace the T-stat and ignore it, since
> next time somebody else might be driving and not notice the gauge creeping
> up (the head seems fine now, I think I got off the road in time).
>
> I guess I could pull the water pump, and take it apart. The impeller
could
> be loose on the shaft? What else could cause an intermittent problem like
> this? I'll isolate the heater core and flush it out, but the coolant
looked
> clean (1 year old) when it blew up in August, and I flushed it and it
looked
> fine in September after I put it back together.
>
> I'd really like to see the cause of the problem (vs. replace a couple of
> parts) so that I can convince myself that it's really fixed this time.
>
> Any ideas?

I'd go for the radiator or the electric fan (if it is indeed an electric
one) that cools the radiator. If the fan is not turning on (or is
intermittently not working when needed) that will cause an overheat. Also
if the radiator is clogging up that will reduce the cooling capacity also
causing the symptoms you described.

"saabturbo" > wrote in message >...

> I'd go for the radiator or the electric fan (if it is indeed an electric
> one) that cools the radiator. If the fan is not turning on (or is
> intermittently not working when needed) that will cause an overheat. Also
> if the radiator is clogging up that will reduce the cooling capacity also
> causing the symptoms you described.

I'd think a radiator or fan problem would have the water in the
radiator, and the top hose, hot. Also it was a cool night when the
gauge pegged (after not overheating on 75 degree days the previous
week).

"saabturbo" > wrote in message >...

> I'd go for the radiator or the electric fan (if it is indeed an electric
> one) that cools the radiator. If the fan is not turning on (or is
> intermittently not working when needed) that will cause an overheat. Also
> if the radiator is clogging up that will reduce the cooling capacity also
> causing the symptoms you described.

I'd think a radiator or fan problem would have the water in the
radiator, and the top hose, hot. Also it was a cool night when the
gauge pegged (after not overheating on 75 degree days the previous
week).