Temp gauge flucuates

My 90 shadow with the 2.5 engines temp gauge flucuates from normal to
almost red line when driving back and fourth, I have replaced the
thermostat,the fan works and the system is full. I have checked for fault
codes and only get the 12 and 55. Can someone tell me what is wrong

 

Do you get plenty of heat from the heater core? If not you may have a
blocked heater core causing the flucuation.

 

Chrysler uses a modular plug which all the dash components plug in to. The
extreme heat in the summer makes the plastic plug expand and looses it's
shape. The male part of the plug is nothing more than a thin plastic strip
with copper glued on the strip and it bends in the femal slot to make
contact. Over a period of years the femal plug looses its ability to keep
good contact. Pull the dash out and use a thin scribe to bend up the
contacts in the femal plug then slide it back together.

HarryS

 

Er...no. That is not the cause of this guy's problem. If it were, his
temperature gauge would periodically drop from Normal to Low.

 

Assuming you properly bled the air from the cooling system, your head
gasket is most likely going or gone.

DS

 

A blown headgasket would cause loss of coolant I believe he stated that the
system was full.

If the heater core is stopped up, it will cause temp fluctuation, If the
coolant does not flow thru the head as designed. Once again, you would have
to experience these type of problems in the field to see this. I have
replaced many head gaskets for a similar problem in the past but the
customers normally complain of adding coolant and not seeing where it is
going.
I have replaced many heater cores because of lack of heat and temp
fluctuation

 

I dont have much heat at all coming from the heater. I had the head gasket
replaced last year and just recently replaced the thermostat to get more
heat.But that didnt help.
How would I be sure it is the heater coil causing this

 

You could disconnect the heater hoses from the core and connect
them together to form a bypass loop, then drive the car and
observe the temperature gauge behavior.

If the car has AC, you could set the controls to recirculate,
this should switch the bypass valve in the heater hoses to bypass
the core.

I've had positive results doing a chemical back flush on these
heater cores when they plug.

You could perform a cylinder leakdown test with the radiator cap
off, watch for any bubbles at the radiator fill neck, the bubbles
may be small or , you may get a gusher of coolant once compressed
air is applied to the cylinder, either indicate a combustion
chamber leak. You might get the same results by removing three
spark plugs and cranking the engine and watching for bubbles at
the fill neck, repeat for the other three cylinders.

Just because the head gasket was replaced last year doesn't mean
there isn't still a problem, the job could have been done wrong;
a warped cylinder head may have been ignored, the head bolts may
have been reused, improper torque procedures may have been used,
the surface finish on the head may have been wrong, the gasket
may have been damaged upon reassembly or the cylinder head may be
cracked.

 

Remove the hoses from the heater core and connect them together and drive
the vehicle as you would normally do and see if it corrects the problem. My
guess is that it will. If you had a cracked head, or any type of internal
leak you would be adding coolant. Dont waste your time on those test right
now. If the core is stopped up, remove and replace it,

 

Thank you Max. I removed the hoses from the coil as you suggested and
connected them. Temp gauge never went above normal as I drove it. So now
that I know it is the heater coil is it worth replacing and how much would
that cost

 

Thats a decision you have to make as far as is it worth it, It has been
about 10 to 12 yrs since I pulled the dash on that particular vehicle, The
shop may charge you anywhere from 4 to 6 hrs to do it

 

Assuming you properly bled the air from the cooling system, your head
gasket is most likely going or gone.



er no Daniel that is not the cause of this guys problem. If it were. he
would be adding coolant, please read the post correctly

 

Hate to be the bearer of bad news, but it sounds like your head gasket
is on its last legs. When I was having early symptoms of head gasket
failure, I went through four thermostats in a 1 month period because I
thought they were just bad since I was having temperature swings. One
way you can lessen the temperature swings is to take the thermostat out
and drill a 1/8" hole. Install the thermostat with the hole at the top.
This will allow any air from the head gasket to escape allowing the
thermostat to open better. However, the head gasket will still need to
be replaced

Other ways to confirm a bad head gasket:

1) When the engine is warm and at normal operating temperature after
driving for about 15 minutes, park the car, but don't shut the engine
off. Open the hood and go to the overflow bottle by the radiator for
the engine coolant. Take a good look at the fluid in there. If you see
some bubbles, then your head gasket is going bad. When my head gasket
started to go, this was the first symptom I had. Also, check for
foaming/bubbling in the radiator while the engine is running with the
radiator cap.
2) Do you see any clouds of white smoke from the exhaust even after
engine is warm? If so, this is caused by coolant being burned in the
cylinders. If this is happening, expect to have problems with catalytic
converter and O2 sensor later on after getting head gasket repaired.
Coolant will poison them.
3) A blown head gasket will cause combustion pressure gases to get into
the cooling system. This is most likely the reason why your temperature
gauge is swinging. The gases cause the thermostat to stick closed
making the engine overheat before it opens. Do you notice coolant
puking from the overflow bottle especially after driving for a while?
If so, this is from the extra pressure due to leaking combustion.
4) Check your oil for contamination. A blown head gasket, when bad
enough, will leak water/coolant into the crankcase. If so, your oil
will look like chocolate milk. Also, check under your oil cap for white
residue. When water gets into the oil, it can create white goblets
under the valve cover. Anyway, if these haven't happened yet, don't
wait until your oil becomes chocolate milk before you change the head
gasket. If this did indeed happen, though, get it fixed IMMEDIATELY!
That stuff will eat up the bearings and bottom end of the engine fairly
quickly.

 

Thats a good way to blow your radiator seams also, not to mention alot of
other problems. but the OP stated he had his headgasket replaced. Then
posted and e mailed me that it was his heater core. After he bypassed it
the problem was gone. He is now in thr process of replacing his heater core.
Glenn Beasley
Chrysler Tech

 

Are you SURE you have ALL the air out of the system? Many of the 2.2/2.5
cars were notorious for doing exactly what you describe if they had a
bubble of air trapped in the system after a fill/flush.

FWIW- the 2.2/2.5 do sometimes blow head gaskets, but its not NEARLY as
common on them as it is on the later 2.0/2.4.