[Doug D]

Could be a radiator scaling up. Might be very early signs.

When I have had a radiator that had become clogged or scaled up, the typical symptom was running hot at highway speed (gauge at 3/4 or so), but not overheating and then dropping to normal (about 1/3 or so) when idling in traffic. A new radiator and fresh coolant cured the issue. This happened on both Acclaims I had ('90 &'92). The '90 did have some fins missing or corroded. I don't recall any fins missing on the '92 when its radiator was replaced, but that was long ago - my memory is somewhat hazy on that.

I'm assuming it is the original radiator. Correct? If it is, it certainly wouldn't hurt to replace it since you just replaced the HG and the vehicle has nearly 200K. I wouldn't want to redo the HG just because of an overheating issue that could have been prevented.

 

[Bob ONeill]

If you are idling or in traffic the fan may not come on because the coolant temp isn't high enough. I try to never run the car without the A/C running. This causes the fan to pull air through the radiator. Even so, the coolant gauge will creep up to about half sometimes especially if the fan doesn't come on. As soon as the car is moving again the temp falls back to 'normal'. So in other words, I think you're dealing with a normal event with the exception of the heater core issue.

 

[Bob Lincoln]

No, Bob, this is definitely not normal. Remember, it's been single-digit temps up here, and today it did hit 34F.

These cars have NEVER hit the 2/3 mark on the temperature gauge for me, unless there is a problem. And they rarely have gone to the halfway mark. Since doing the head gasket last March, the temperature has been almost exclusively at the warm mark, and no higher than the 1/3 mark, ever, in all these months.

No, it's acting more like trapped air. However, this business of the radiator being cold at the cap after 40 miles of driving just doesn't make sense. Tonight it crept almost to the 2/3 mark, and then fell back to just below halfway. At highway speeds it's been staying in the normal range, between warm and 1/3. Until the past couple of weeks, it's been there all the time.

The heat is normal and constant from the core. Since I replaced the jug, there's been no coolant loss or odor. But I had removed the heater hoses from the core to bypass it, before I discovered the jug leak, so I did introduce some air. I burped it as always, but nothing really bubbled up at the cap. The level just climbed as I ran it, until it started to spill over and I put the cap on.

When I got home tonight, it was at the 1/3 mark, and I let it idle a minute or two until it hit the halfway mark. It stayed there, so I turned on the defroster to force the fan on. The fan cycled on 5 seconds, off 5 seconds, repeatedly. That doesn't seem normal, either.

 

[deder_2]

Is it possible the temp sensor is bad. My wife came home the other day from shopping and I had some errands to run so I grabbed her car. Got a couple miles down the road and the temp gauge was at 3/4. Pulled over and it started to climb, so turned the heat on high(I live in MN so the heat was already on) and it barley moved. Drove home and popped the hood. Noticed the fan was on, but not on high. Felt the cap, ice cold. Weird I thought. Let the car run with my hand on the cap, never got hot enough to take off before the fan came on. To make a long story short, I got a new water pump, radiator, thermostat. Guess what, the f***ing problem still happened. Replaced the temp sensor that was replaced 2 weeks before because it just failed, and the temp was normal. I never really messed with a car when its this cold out, but I would of thought the cap would still get hot enough that you couldnt hold the hand there. Guess I was wrong. The thing that probably could have saved me some time was that if I turned the car off and immed turned the key to run not start, so the gauges would come up. The temp gauge wouldnt come to the same position as when the car was running before i turned it off.
Im sure this may have nothing to do with your problem, but please look at the simple things first. Do as I say, not as I do..

 

[bamman]

When I got home tonight, it was at the 1/3 mark, and I let it idle a minute or two until it hit the halfway mark. It stayed there, so I turned on the defroster to force the fan on. The fan cycled on 5 seconds, off 5 seconds, repeatedly. That doesn't seem normal, either.

That would be normal if your A/C wasn't charged. The fan only turns on when the a/c clutch is engaged. The a/c clutch is only engaged if the low pressure switch is closed. The low pressure switch is only closed when there enough freon in the a/c system.

 

[ChargedDust]

Have you checked the little hose from the overflow bottle to the radiator to see if it's clogged, or maybe the nipple on the radiator itself.

 

[Bob Lincoln]

Yes, they are fine. Now that the jug leak is gone, the radiator siphons fluid back from the jug as it should. Cap appears to work normally. It's just cold after a long ride, when it should be uncomfortably hot.

This morning, it was 41F, so it warmed up faster, got to the 1/3 mark within 2 1/2 miles, and on the highway part of the ride (about 30 miles) it stayed about halfway between warm and 1/3, very stable. At the end, in 2 miles of traffic, it crept about a needle's width beyond the 1/3 mark, whereas yesterday at the same point, it was just a hair above the halfway mark. So maybe air is purging still. The heat was strong and normal with the outside temperature so much warmer today. It's supposed to hit 55F by noon.

That would be normal if your A/C wasn't charged. The fan only turns on when the a/c clutch is engaged. The a/c clutch is only engaged if the low pressure switch is closed. The low pressure switch is only closed when there enough freon in the a/c system.

A/C is fully charged and works fine. Thermostat works fine, new last year. The temperature sending unit, I trust. The engine itself gets to normal temperature fine and feels hot to the touch, as does the top radiator hose. Thanks for the input. The next few days should tell me if it's stabilized or if something is still wrong.

 

[CudaPete]

Sounds like a circulation issue. Is the water pump good? Do you have a lot of calcium build up in the radiator?

 

[Bob Lincoln]

The water pump, thermostat, all hoses and belts, coolant were all new last March when I did the head gasket - 9,000 miles ago. The radiator looks fine from what I could see down the neck, and the fins are all intact and not blocked. If need be, I have a spare radiator from my 92, which I replaced in 2004 and has 70,000 miles on it.

Today it behaved better, so maybe the air is gradually bleeding out. If it doesn't go to the halfway mark tonight, I'll feel better about it. But no antifreeze smell, no window fogging, so I think that was all due to the leaking coolant vaporizing and getting sucked in the cowl. So at least the heater core appears to have been a false alarm.

 

[Bob Lincoln]

All the way home tonight it was between warm and 1/3, with the worst excursion in traffic being about one needle's width beyond the 1/3 mark. Never got near the halfway mark, and it was 57F today. Changes in reading were slower. Heat was normal. The radiator cap was much warmer, but tolerable to the touch. All hoses hot, with the expected differential between in and out on both the heater core and the radiator. The overflow jug was down a little, the radiator was full. That tells me that it burped a little air and the fluid from the jug was sucked back into the radiator to replace the volume. I topped off the jug tonight and will monitor it.

Tomorrow night I do a lot of city driving, so that will be the ultimate test. I have coolant with me, but don't expect any trouble. Seems as if the entire experience was a cracked overflow jug combined with trapped air. I've never had any trapped air from cooling system work beyond the initial bleed, which is why this puzzled me. But I've never disconnected just the heater hoses and reconnected them again without draining the whole system.

 

[Doug D]

Sounds like it's back to normal. After my commute home (58 miles one way) I checked the cap on the Ram - it was lukewarm. Not cold, not hot.

 

[1991spirites]

Temp gauge issue sounds normal to me. On every 2.2/2.5 car I have ever owned, sitting in traffic the temp gauge hitting halfway is normal since that is were the fan kicks on.except for my Spirit turbos in which it would go pass half way before the fan kicks on. Once the temp comes down which is 1/4 on the gauge the fan kicks off. Normal highway driving is about 1/4 on the gauge and stop and go half way on the temp gauge.

 

[Bob Lincoln]

For a car which has everything in good working order, that wide a range is not normal. But most of these cars run hotter than mine due to a combination of missing fins, blockage, deteriorating head gasket, etc. Since I replaced the head gasket, up until recent weeks it has not gone over the 1/3 mark ever, under any conditions. It's been remarkably stable. Part of that may be the Stant Super Stat thermostat, which is a higher-quality, better performing thermostat than most out there. It's also $17.

 

[1991spirites]

Maybe the sensor for the gauge is acting up, or maybe the actual cluster is acting up. 90-93 Clusters are know to start acting funny from time to time. Pretty much all my cars over the years acted the same weather they had 46K miles on it with new everything to 150K miles on it that have been neglected. My Chrysler 200 acts the same way, temp gauge fluctuates quite a bit from city vs highway driving.

 

[Bob Lincoln]

Nope, all's good now.