Fan is tight, as is the shroud. It was my first suspicion actually, since Oskar would cool down back to normal as soon I picked up speed...

Most head gasket failures are caused by overheating, and since my engine just started acting this way recently, and hadn't been overheated beforehand, I'm still skeptical about the gasket.

Wouldn't the engine overheat continuously if the gasket was damaged?

I'll try the Block Test Kit tomorrow, grudgingly, since I've just dropped $40 bucks for the acid dip on the radiator, but It's the last sure way I know.

Also, is there a way to test flow in the radiator? Would the acid dip flush out even the most stubborn of clogs?

PvN

If you have a lot of calcite then an acid dip might not get it all out. See what it does cold with the radiator cap off tommorow. You have to have the radiator cap off anyway to do the block test. If it gushes out then dont waste you money on the block test kit, that would indicate the head gasket has failed.

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1981 300D 147k
1998 VW Jetta Tdi 320k
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I love the smell of diesel smoke in my hair

so maybe there is a timing problem.

i am not sure about a diesel but with a gasser if the timing is retarded it will run very hot.

i just dont see how a diesel will run hot at idle. personally i am not sure if you could get it hot enough to damage it by letting it idle even with no water at all. i wouldnt want to try this, though. just making a point. not much heat generated at idle.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I had a similar problem a few months ago with a 123 it was a clogged radiator, at the radiator shop the guy did this “test” with the engine off but engine at operating temperature he squished his hand between the fan and the middle part of the radiator he just touch the middle part and the sides it was cold and hot at the sides, I did the same “test” and he was right on his verdict a partially clogged core so he rod it out and problem fixed, try this “test” and see what happen.

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2005 S500
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61 300 restoring

Personally, I don't believe you have a head gasket problem by your symptoms.

Pressure in the cooling system to the point of overheating won't disappear when you drive the vehicle at a faster speed. It would continue to overheat.......perhaps more so.

I'd get the test kit from NAPA just to rule out any possibility of combustion pressure in the system.

Additionally, after running it and letting it sit overnight, open the cap and listen for escaping pressure. Don't confuse the noise with a slight vacuum which will present a soft "whoosh" and air will enter the system. There will be a definite pressure release if you've got head gasket issues.

Finally, the shop might have done an acid flush of the core, but, did anyone do a thorough cleaning of the external fins? These vehicles have very fine passages through the fins and it takes quite a bit of time and chemical to get them completely clean. I've spent over two hours on the SD's radiator in an attempt to fully clean it. Then, hold it up to the sun and peer through the passages. Any obstructions will be visible. Time to clean........yet again.

I still need to find some professional condenser cleaner to speed this process.

I'm fairly convinced that you still have radiator issues........either external........or internal........no guarantee that the "radiator shop" did the proper job........like everything else in this world.

I wonder if the block test kit will work on a diesel. It detects carbon monoxide in the cooling system and thats something thats almost non existant in a diesel thats not under a heavy load. Years ago we used to just use an exhaust gas analyzer to detect CO in the cooling system if we suspected a bad headgasket but I dont remember it working on diesels.

i agree with brian.

flushing wont help clogged fins.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Replace your radiator.
A head gasket will make the engine run hotter the faster you drive, not make it cool down at highway speeds!
Heating up at idle only is a symptom of a blockage allowing only partial cooling.

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1968 230S Automatic, Elfenbein
1975 O309D Executive Westfalia Camper Bus, Blau/ Weiss
1972 280SEL 4,5 Dunkelrot
1966 VW Type 34 "Grosser" Karmann-Ghia
1963 VW 1500 Variant Pearlweiss
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1971 VW Squareback Automatic, Clementine Orange
2001 E320 4Matic Wagon- Our belated welcome to the 21st century! Polar White
1973 280SEL 4,5 Sliding Roof "The Bomb", Dunkelblau.

I've gotten so many advices, and am very thankful.

I've started the engine cold today, with the cap off of the radiator, and no gushing fountian of green fluid...so...if there is a hole in the gasket, it must be a very small one.

I tend to think I have a coolant problem, not a head gasket problem, (of course I really want a coolant problem at this point!)

I think this way mainly because of the rampant fluctuations of engine temperature, sometimes hot, sometimes not.

Today I checked both the old and new thermostat I have on the stovetop, both opened correctly. The old one was rated for 79C, so I reinstalled that one, and the car seemed to run well, It didn't creep up like I had been doing.
So I'm going to take a drive into a beautiful North Carolina afternoon, and see how he acts...

waht part of NC are you driving through?
I am in the charlotte area, Good luck with the radiator problem, and I am glad no bubbles showed up in the radatiator test. If your rad has already been acid cleaned, a new one may be the only hope. I agree that this does not sound like head gasket problems, but a partially blocked rad. Odd how almost all mechanic shops point to the head gasket when odd overheat/high temp problems happen, even when it fails the bubble test. hot at idle means not enough coolant flow, or not enough air flow across the rad. since you have solid fan, and you are sure the belt is not slipping, start planning a rad replace.
John

It's the intermitteness of the overheating, and the fact that the radiator doesn't get hot, (around the fins, boiling at the top) that is still pushing my buttons..i'm going to make an appointment at the local shop, but afraid they will just charge me for all the same information you guys have given me for free...

Are you sure you filled the system completely with coolant? I had an overheating issue once after flush/fill that we due to air on one side of the thermostat (even though the radiator/overfill tank was full of coolant)...

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1985 MBZ 300DT
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1981 VW Vanagon