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Overheating - Correlations

Old 02-22-2015, 08:53 AM
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Join Date: Jan 2015
Location: Charlotte, NC
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Default Overheating - Correlations

I own the dreaded '91 350SDL. Car runs great - just replaced the radiator with a custom-made all aluminum one - it's a work of art. Old radiator was leaking, and car would get warm (not dangerously hot). Could not find an OEM or good aftermarket, and salvage wasn't an option as I'd still have 24 year old radiator problems. It was running hot, and with the leak, couldn't really pressurize the system, so that was the first thing to get checked/replaced.

I'm still seeing it run over normal temps, even on cold days. They've checked for exhaust gasses in the coolant - none. No coolant in the oil, either, so they don't think it has a cracked gasket or head.

In doing some research, I have found that exhaust blockages can cause an engine to run hot (it runs 100 - 105c) on the highway at 70mph, but it's also winter.

What I have noticed, is a very strange exhaust vibration - around 1800rpms, the exhaust 'rattles' in the rear of the car. Especially bad when it's very cold out, but once the car warms up, it's quieter - but still there. More of a rumble/vibration.

So thinking I either have a collapsing radiator hose that's suck shut, a bad water pump, or an exhaust issue. The only other thing I can think it could be is just a bad coolant temp sender - that's cheap and easy enough to change out - so may do that as first step. Or should I take it somewhere else and have the coolant test re-done?

The car just turned 116K - it uses zero oil, and is in perfect condition otherwise - beautiful car and a total pleasure to drive. I just need to get this overheating issue solved - if it needs a head gasket, so be it. But I don't want to go chasing a rabbit down a hole. Love this car, and in a couple of years would be willing to put a good rebuilt (upgraded) ening, or a 606 in it if I can find a good used one.

Any thoughts out there (aside from sell the car). I know these engines are problematic - but so far it doesn't use a drop of oil, all service has been done on it from day 1) - just want to get the overheating issue solved and get a few more years out of it before replacing the engine.
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