Using a Block Tester

One of my recently-acquired CUCVs has paperwork in the truck indicating that it has at least one blown head gasket. I bought a block tester kit at NAPA to help me figure out whether it really has a blown head gasket, or if that was just written on the paperwork to make the truck fail so that the unit could get a new truck. I've seen a block tester used before (back when my HMMWV blew its head gaskets), but I haven't used one myself. I'd like a bit of advice from sombody who has used one before.

The instructions say to warm up the vehicle until the thermostat opens, and then remove the radiator cap to use the tester. That seems like a good way to get burned to me.

1) Can I just take off the cap before I start the engine, and let it warm up with an unpressurized system?

2) How will I know when the thermostat has opened?

3) Will my 6.2 diesel warm up enough sitting and idling? I recall that my HMMWV usually takes a good 10 miles of driving to get up to full operating temperature, but I don't know when the thermostat opens up.

I'm crossing my fingers that the gaskets aren't quite as blown as the paperwork claimed. Another CUCV from the same batch supposedly had a slipping transmission, but I think it just needed a new cap on a vacuum line tee.

Thanks in advance for advice!

It's been years since I used one (still have it somewhere) but, removing the cap while under pressure is dangerous, so warm it up without the cap. Two ways to tell is to watch the coolant start to move (thermostat opens), and by checking coolant temp with a thermometer in the radiator neck.

Ditto on removing the cap and warming up. Does it have coolant in the oil? Sometimes diesels don't show up on the block testers, the end combustion result is different than a gasser.

Would an oil analysis show coolant in the oil? Might want to have that done if the block tester shows negative.

I haven't seen oil on top of the coolant or coolant droplets on the dipstick, but I haven't run the engine yet. I tried to change the belts today (right alt belt is missing), but I got hung up on the PS pump belt for lack of a 15mm deep socket. I plan to pull the glow plugs before I crank it for the first time, in case there is coolant in the cylinders. I bought a couple of oil analysis kits at NAPA the other day. A friend of mine thinks there's not much use in analyzing the old oil since it could have extra crud and water in it from sitting for who knows how long, but if the oil analysis checks specifically for antifreeze then I figure it's worth the $14 just to check for that and ignore the rest of the analysis.

Will it warm up enough to open the thermostat just idling in park?

Will it warm up enough to open the thermostat just idling in park?

Click to expand...

Yes, give it about fifteen minutes or so, but watch the coolant when the cap off.

Re: RE: Using a Block Tester

319 said:

Will it warm up enough to open the thermostat just idling in park?

Click to expand...

Yes, give it about fifteen minutes or so, but watch the coolant when the cap off.

Click to expand...

I'll wear safety glasses and hum "Shake Hands with Danger"!

RE: Re: RE: Using a Block Tester

Blocking airflow threw the radiator with a piece of cardboard will help it heat up faster. If these have a gauge watch it at the same time and see how wel it seems to work.

RE: Re: RE: Using a Block Tester

No gauge, unfortunately. Just idiot lights. Great, big 2" diameter idiot lights where there ought to be gauges.

I plan to keep the truck mostly stock, but I'm tempted to add some more gauges to it.

RE: Re: RE: Using a Block Tester

You can also tell when the thermostat opens by feeling the upper radiator hose. It will become very hot & you will see coolant circulating. When the thermostat opens, she's up to temperature.

RE: Re: RE: Using a Block Tester

Mark, try to turn the engine 1 full rev by hand....a wrench.... If it turns over, there is no coolant in the cyls. Are there any signs of external coolant leaks under the truck, by the pan rail? Hows about the radiator? Is there any signs of carbon on the cap or floating on top of the coolant?

RE: Re: RE: Using a Block Tester

Thanks for the advice! I'll take a look underneath for leaks when it's light outside. I haven't noticed any carbon on the coolant or cap so far.