Loosing Coolant

[MIKE_JAMES]

I have a 1983 Chev Pickup with a 1984 6.2L Diesel
I have recently had a transmission overhaul and a new fuel pump fitted. The first trip I did after this the motor overheated after about 100 kilometers distance while doing 100ks per hour,I slowed it down to about 50ks for a short distance and the needle came down so I took it back up to 80 ks and stayed at that for the rest of the trip. When I stopped the truck the radiator appeared to be under pressure and discharged water through the overflow tank. This has happened several times since then.
There is no sign of any water in the engine oil, no moisture blowing out of the exhaust, the radiator fluid appears to be normal,we took the glow plugs out and turned the motor over, there was no signs of water, yet the radiator is under pressure. Any ideas??? HELP

[ZZ]

Check to see if the coolant in the overflow tank is swirling/gurgling while the engine is idling. This is the 1st & easiest check for a blown head gasket or a cracked head. If either is the case, the exaust blows into the cooling system.

[TimK]

Mike,

It's normal for the radiator to be under pressure when the engine is operating. Even some gurgling of the coolant into the overflow tank is normal. However, excessive pressure is not normal. This may be as simple as a bad coolant thermostat.

TimK

[MIKE_JAMES]

Thanks for the replies. The thermostat appears to working but I do have bubbles in the overflow tank. This is probably a silly question but does anyone know if air could get in through the inlet manifold, as this was off when the truck was in the shop to get the fuel pump done. We had no problems with the cooling until the day after it came out of the shop. We can't take it back to the shop it took six weeks and lots of $$$ for them to do the pump and we need the truck now!!

[john8662]

The intake manifold does not have coolant ports in it like the SBC gassers do. Why did you have the Injection pump replaced, due to a certain running condition? From your description it sounds like it is head gasket time.

[MIKE_JAMES]

Had the injection pump replaced as the motor would just cut out when driving at normal speed and would rev like crazy but go nowhere when stopped at traffic lights etc. This fixed the problem, the truck goes like stink normally great get up and go.
We decided to bite the bullet and took the heads off today we can see a small amount of pitting on the back righthand side and the front lefthand side on the outer side of the cylinders. We also found very small cracks around the glow plug ports. We are thinking of having the heads planed before we put the new gaskets on.We have to wait for the gaskets to come from America anyway so we have plenty of time. Last time we did a job like this was on a 6cyl petrol motor in 1976!! Will keep you posted

[DmaxMaverick]

....We also found very small cracks around the glow plug ports....

If you mean small cracks radiating from the flash hole on the pre-cups, they are normal as long as they don't cross the head gasket fire ring. As long as there are no chunks coming loose and the cracks are hairline, usually near the corners of the hole, they are not an issue. Pitting in the may be indicative of something else, not necessarily coolant, and could be from a previously repaired problem. Pitting takes time to manifest, and usually requires a long period of sitting. This can happen during storage, and moisture can develop in higher humidity areas with significant temp swings. Could be the engine was stored for a period under those conditions.

With a head gasket failure, the engine can pass a lot of coolant and leave no sign of it. If the coolant loss is a recent issue, I would discount what you've found so far as a contributor.

Good luck, and keep us posted.

[mhagie]

I had a 5.7 Olds diesel that I had the engine blueprinted and I know for it if you surfaced the heads to true them up you used a different Fel-Pro head gasket that was slightly thicker to make up for lost material and keep the compression ratio from climbing.
Does that apply to the 6.2 as well?
Merle.

[DmaxMaverick]

Originally posted by mhagie:
I had a 5.7 Olds diesel that I had the engine blueprinted and I know for it if you surfaced the heads to true them up you used a different Fel-Pro head gasket that was slightly thicker to make up for lost material and keep the compression ratio from climbing.
Does that apply to the 6.2 as well?
Merle.

Yes. There are oversize head gaskets for that purpose. Some here have even considered using them to lower the compression ratio (thicker gasket, no milling), as opposed to lower C/R pistons.

[arveetek]

I believe that you only need the thicker head gaskets if you have the block resurfaced, not the heads. I'm in the middle of my engine rebuild project right now, and I specifically asked Benny Avant about this question. He said resurfacing the heads doesn't really bother the compression ratio, but resurfacing the block does.

When you plane the heads, you're not changing the combustion chambers all that much. However, on the 6.2L, when you plane the block, the pistons stick up out of the block farther than before, causing higher compression ratio, and perhaps even having the piston contact the heads/valves.

You should be fine using standard thickness gaskets and having the heads resurfaced.

I'm having both the heads and the block resurfaced. Benny is building me custom pistons that have the wrist pin located higher in the piston to compensate for the lower deck height. He's also shaving another .010" off the pistons to lower the compression ratio. The pistons will then be ceramic-coated to be heat-resistant. Even though I'll have a planed block and heads, I'll be able to use standard head gaskets due to the custom pistons.

Thicker head gaskets worry me, as they might be weaker and blow out down the road sometime.

Casey

[DmaxMaverick]

Oops. Wrong engine. Had a senior moment (practicing).

Thanks, DD......You're not so dummy

[ 03-26-2005, 10:03 PM: Message edited by: DmaxMaverick ]

[dieseldummy]

Dmaxmaverick, Your theory of .010" of either side is the same isn't exactly true. When .010 is milled from the block the pistons phsicly stick out that much further. When .010 is taken off of the head all that changes is the valve resesses are smaller and the precup opening is a little smaller as well because our heads are flat. Any good rebuilder will correct the valve issue by grinding the seats to offset the lost material on the head surface and the little bit lost in the precup opening wont amount to much in the end. The majority of the combustion chamber is in the precup its self and the remainder is in the recardo resess on the piston. Not to start a fight here, but that's the logic behind Benny's advice.

[MIKE_JAMES]

Thanks for all the advice we have certainly learned a lot in a short time. Since last time we have found out the truck was stored for a few years.The heads have been hot water pressure tested at the machine shop, they held the pressure OK so decided to have them planed to remove slight pitting we found earlier. We are ordering a new set of gaskets from Northern Autos but they have to know if it is a light or heavy duty engine - that tells them which intake gasket we need. We have no idea how to determine if it is heavy or light, all we know is the intake manifold is cast aluminium has no 14071075 on it.
HELP!!