1991 Dodge Shadow Cooling System Issues

I have a 1991 Dodge Shadow ES convertible with 2.5 Turbo engine. I have recently encountered a strange problem with the cooling system. Or at least the symtom of my problem appears in the cooling system.

When ever I start the car cold after letting it sit more than 24 hours, I encounter the following scenario:

For the first three miles of driving, the temperature gauge will slowly climb from C to full H. Then it will quickly drop to the first hash mark at the low end of the driving range, then settle at the second hash mark, approximately 1/3 up the gauge from C.

When I have caught this at the right time, I discovered that the upper radiator hose was cold to the touch while the temperature gauge was hovering at H. When the gauge drops, the upper radiator hose is now warm, indicating that the thermostat is staying shut while it heats to H.

After it did this to me the first couple of times, I instinctively replaced the thermostat (thought it was bad) and flushed the cooling system. Now, with new thermostat and new coolant, it is doing it again. It won't do it if I drive the car daily, only when it sits over 24 hours. Since I flushed the cooling system, the water level in the overflow tank has dropped slightly, but there is no evidence of an external leak.

Has anyone else out there experienced anything like this before? I have heard of engines acting this way if you don't bleed the air out of the thermostat chamber after a flush. Could I somehow have an internal coolant leak causing an air bubble behind the thermostat after it sits for 24 hours?

Any thoughts on this would be greatly appreciated.

I have a 1991 Dodge Shadow ES convertible with 2.5 Turbo engine. I have recently encountered a strange problem with the cooling system. Or at least the symtom of my problem appears in the cooling system.

When ever I start the car cold after letting it sit more than 24 hours, I encounter the following scenario:

For the first three miles of driving, the temperature gauge will slowly climb from C to full H. Then it will quickly drop to the first hash mark at the low end of the driving range, then settle at the second hash mark, approximately 1/3 up the gauge from C.

When I have caught this at the right time, I discovered that the upper radiator hose was cold to the touch while the temperature gauge was hovering at H. When the gauge drops, the upper radiator hose is now warm, indicating that the thermostat is staying shut while it heats to H.

After it did this to me the first couple of times, I instinctively replaced the thermostat (thought it was bad) and flushed the cooling system. Now, with new thermostat and new coolant, it is doing it again. It won't do it if I drive the car daily, only when it sits over 24 hours. Since I flushed the cooling system, the water level in the overflow tank has dropped slightly, but there is no evidence of an external leak.

Has anyone else out there experienced anything like this before? I have heard of engines acting this way if you don't bleed the air out of the thermostat chamber after a flush. Could I somehow have an internal coolant leak causing an air bubble behind the thermostat after it sits for 24 hours?

Any thoughts on this would be greatly appreciated.

How old is the new thermostat? I have seen some that fail in a month, these are the cheap aftermarket ones. I would switch to a Mopar thermostat if for no other reason, just to eliminate a problem area. Some thermostats also have a small hole or valve on the flat plate that alows air to pass through.

could be a head gasket . As in getting exuest bubbles into the cooling system . To check when cold take the rad cap off and start the engeine and rev it up if the coolent shoots up in the air then your gasket is probly shot. Wont do it when worm because the gasket seals better .

Hey guys, thanks for the advice. Here is an update as of today. I removed the thermostat, which is only two weeks old, and drilled a 3/32 weep hole in the body to allow for air release. I put it back together and took it for a drive. No overheating problem as of yet. But a few minutes after I parked it, I saw coolant dripping on the ground. I opened the hood and found a pinhole leak in the radiator, along the seal between the plastic side tank and the core. Now I know where the coolant has been disappearing. This morning, I popped off the radiator cap and started the engine cold. Coolant did not escape or even rise in level, so I think the head gasket is good for now.

Does anyone know if anybody makes an "all-metal" radiator for these cars? This is the second plastic radiator that has leaked on me like this since I bought the car 13 years ago.

I don't know of one offhand; just Google Dodge Shadow radiator, there are numerous sites.

Thanks for the reply. I did just that and got a new radiator delivered to my door for 45% less than what I paid for the last radiator five years ago. Unfortunately, there are no "all-metal" replacements available. I replaced the radiator last weekend. So far, it has worked just fine. This time I found a fatigue crack in the metal along the metal edge that crimps around one of the plastic tanks. Looks like I'm good for another five years.

Five week progress report:

My Shadow runs just fine with the new radiator, with no more overheating problem.

Five week progress report:

My Shadow runs just fine with the new radiator, with no more overheating problem.


Good work! Thx for getting back to us.:)

Two month progress report:

No overheating problems since the last update.

I have noticed a strange condition with my cooling system, however. When the car is warm and idling in the driveway, I notice a steady stream of bubbles coming up through the coolant in the overflow tank. Then, when I removed the radiator cap (when warm) with the car idling, the bubbles pop up out of the coolant in the radiator. When I raise the rpm, the coolant becomes ariated with small bubbles and gets a little foamy. Drop it back to idle again, and the steady stream of bubbles occurs again. Now, if I remove the cap when it is cold and start the car. I don't see the bubbles like I did when it was warm.

Also, I now have a granular residue coating the inside of the radiator. This residue is dark brown and feels mushy. Strange to have this, especially since I replaced the radiator and flushed the system only two months ago.

Is this condition indicative of a head gasket beginning to fail? This is a 2.5 Turbo with 116,000 miles. The head has never been off since I have owned it and I bought it in 1993 with only 12,000 miles on the odometer.

Any thought out there would be appreciated.

The sludge could have been in the system, and has now gotten loosened up and is showing up in the radiator.

You may have trapped some air in the system; try parking the vehicle facing uphill. Take off the cap, start it up and let the thermostat cycle several times, keeping it full. The bubbles should pretty much quit.

Thank you for the comment about the trapped air. That theory seems plausible if I had just refilled the system. But after two months of operating the car since the radiator replacement, I would expect any trapped air to have expelled long ago. But then again, anything is possible.

Are there any other opinions out there on this subject?

Well folks, I decided to visit my local auto parts store to ask them about my problem and how to investigate it further. They sold me a device called a Universal Block Tester. This consists of a glass tube with rubber plugs on each end, that you insert into the opening of the radiator, while the car is hot and idling. You then pour into the tube, a pre-measured amount of blue fluid. Then you sit there and watch as gases bubble up from the cooling system and through the blue fluid. If the fluid turns from blue to yellow, then you have confirmed a combustion gas leak into the cooling system, from either a cracked head, cracked block or bad head gasket.

Well, I took it home and performed the test on the bubbly radiator in my Shadow. The fluid turned yellow!! The directions recommended that after a positive initial test, that you disconnect one spark plug at a time and retest with each cylinder dead to see if the leak can be isolated to a specific cylinder. Each time I tested this way, the fluid turned yellow, indicating that I am leaking on more than one cylinder. This condition is indicative of a bad head gasket.

So, my problem is a head gasket which is going away. Time to get my hands dirty.

BTW, after finishing with the test on my Shadow, I fired up my 1964 Chrysler 300 convertible and tested this beast to see if I have problems with this car as well. Well, the fluid remained blue on this old beast, even though it has the original 383 with 132,000+ miles on the clock.

I recommend this test kit for everybody and suggest testing all your cars whether you suspect problems or not.

Another two month progress report.

My poor Shadow has been sitting in the garage for the past two months, waiting for me to get my hands greasy. Earlier this week, I finally pulled the top end of the 2.5L. This included the head, intake manifold, exhaust manifold and turbo as one unit. Much easier to do it this way than to disassemble each part in the car.

At 116,000 miles, I discovered absolutely no ridging on the cylinder walls. The cross-hatch finish of the cylinder walls was clearly visible. This it a good testimonial for changing your oil every 3,000 - 4,000 miles.

I took the turbo charger to a turbo rebuilding shop. I figured, since I had it out of the car anyway, I should have it refurbished. Up to this point, it has operated flawlessly, except when the vacuum line to the waste gate sprung a leak and kept the wastegate closed. Well, the guy at the shop looked in at the impeller (shiny clean and looking brand new), then spun the impeller with his finger. He put it back in my box and told me to "Put it back on the car"! Good, another testimonial for changing the oil every 3,000 - 4,000 miles.

Next, I took the head to the local machine shop to have it inspected. That's when I found out my poor Shadow was sicker than I thought. The first problem that was obvious to me during disassembly, was a scored path on the cam lobe and follower for the #3 exhaust valve. This required a new cam and followers for the head. Next, all four exhaust valve guides were toasted and required replacement. And last, put not least, all four exhaust valve seats were cracked. I was blowing exhaust gases through cracks in all four exhaust valve seats! I suspect that all of this damage most likely is the result of driving this car for a year and a half with disfunctional waste gate.

Anyway, the head is due back from the shop today. Once I reassemble and fire it up, I will report again.

Hope you'll be back on the road soon...with a new head gasket and all the work done on the head, I'm thinking that your cooling problems should be past.

And while I'm not real knowledgeable about turbos...I do know that driving with the wastegate disabled = :nono:

Well folks, after several months of delays, my Shadow is back together and running. And it is running great! And, of course, no more issues with the cooling system.

Prior to noticing the exhaust bubbles in the cooling system, the car ran well most of the time, as compared to a standard 2.5L. But it just didn't seem quite as strong as it used to. Then, when I punched it to wide open throttle, it would wind up to 4,000 rpm, then stumble and miss and hiccup until I backed off the throttle. Now when I punch it, it will quickly accelerate past 5,000 rpm and upshift to second without hesitation. What a difference!

I did learn one little quirk the hard way. The turbo has both an an oil and coolant supply lines that are held in place by a clamp, which is bolted to the rear end of the head. I had the rubber sections of these lines replaced while they were off. The clamp did not fit over the replacement rubber sections of hose, so I didn't reinstall the clamp or bolt. When I started the engine for the first time, all eight lifters continued to clack like they had no oil pressure, even after the oil pressure was up in the rest of the engine. I then noticed a puddle of engine oil collecting on the ground. It turns out the bolt for this hose clamp also caps the end of a pressurized oil gallery in the head. Once I installed the missing bolt, the lifters were quiet.

I have logged approximately 75 miles on the car since yesterday afternoon and no gremlins have appeared so far. I will keep you posted as time goes on.

Thanks for replying to my thread. I replaced the head gasket and no more bubbles in the reserve tank. I still have a bubble somewhere in the system but I'm working that out. The only problem is now my car doesn't accelerate correctly. I can punch it to the floor and it still goes like i'm barely on it. I checked the Haynes Manual and I checked the fluid so that is not the problem. There are no grinding noises or sliding noises while acclerating and the car still shifts alright but I can't acclerate at all. The book said it could be the Fuel injection system, incorrect ignition timing or maybe the spark plugs (those are easy to check). The thing is with the car in neutral it revs perfectly. It sounds great but when I try to drive it it will not acclerate at all. It takes me about 15-20 second just to get to 25 mph with it floored. I'm not sure what it could be. I'm gonna post up a thread and call around. If you have any suggestions that would be greatly appreciated. Thanks again.

Sounds like the cam sprocket is off by one tooth of the timing belt. You have to really be careful to double and triple check the alignment of the timing marks on all three sprockets after adjusting the timing belt tensioner. My mechanic screwed up when he replaced the timing belt in my Shadow the first time and I had to correct by installation at least once when I put my Shadow back together myself. When it comes to the timing belt, measure twice, assemble once.