Block Test Kit - Overheating 300SD

[cousindave76]

Has anyone successfully used a block test kit on a 617 engine to check for hydrocarbons? The reason I ask is because the instructions for the kit I have found (NAPA kit) says to test from the radiator cap, but since there is not a radiator cap but rather a cap on the overflow tank, I was wondering if it could be tested from there? Also, what kit is recommended? I've seen lots of folks on this forum use the kit and post an "inconclusive" test result.

Why you may ask? If you're interested, continue reading below for the full scoop.

For the first 6 years of owning my 83' 300SD my temp gauge stayed rock solid on 80 degrees Celsius. I live in Dallas so I never hill climbed. But cold or hot outside, 80 degrees and that was it! A year ago I started having the engine temps rise. Now, in hot weather I cannot sit in traffic. The temp gauge will peg red if I let it. When it's freezing to mild temperatures outside, the temp gauge will balance out around 100 Celsius. I've gone through this forum and tried just about every thing. I've flush the cooling system with the soap and descale solutions. I've removed my water pump for inspection, it was fine. I've had three different 80c t-stats. No luck. I've tried many ways of burping the system... including having the front end tilted up higher than ramps can get it. It's burped. Recently I've read many posts saying the temp gauge is likely faulty. In fact, I see many OP's being told that is almost without a doubt a bad temp reading or faulty gauge. With that in mind I bought a an infrared temp gun and found that when my temp gauge is sitting on the 100 degree Celsius mark, the infrared showed the block at 98.5 Celsius. It's been really cold outside since I bought the gun and I have not had a chance to try it when my temp gauge gets REALLY high but I can be pretty sure that this mean when my gauge is saying my engine has hit 120, it is! So if you have a suspected overheating engine, don't let folks tell you it's just a faulty gauge and don't worry about. You MUST shoot the block with a temp gun to find out the facts or you risk blowing your head or worse. I've also checked my aux heater water pump, works fine. I've traded out my fan clutch, no change.

This brings me to the one last thing I can think of that might be causing my over heating. Blown head gasket. But due to the size of the job, I want to be sure. The engine runs fine. It warms up normally. The cooling system seems to be holding the right amount of pressure. I don't have a way of measuring the cooling system pressure but the upper radiator hose is firm and there is no antifreeze being forced out the overflow tank unless the engine gets really hot. The radiator is about 4 years old. The neck of the old one broke off while I was under way and the engine overheated at that time. That's one of the reasons I suspect head gasket. Perhaps overheating the engine a while ago weakened the gasket and now it is finally showing up? Thus, I really need to be able to check for hydrocarbons in the coolant to see if this is the problem.

Long post I know. But I bet many of you out there having this problem can understand the frustration and why I wrote so much.

HELP! If you have any ideas other than what I have tried above I am ALL ears