Frost on vaporizer

[Fisherguy]

Hi, first post hre, got a problem I'm hoping you can help me with. I have a 1990 F250 SC 4X4 with a 460 5 spd running on propane (only) with an OHG mixer.

I've had my 460 on propane for years, never had this problem before.
Yesterday I went out, got about 3 blocks from home, the truck started running terrible, finally stalling.
I pulled over and found the vaprizer was covered in frost as wll as the hose going to the OHG mixer which was also covered in frost.
After many attempts I finally got it running on the side of the road a few times, eventually the engine warmed up so the vaporizer had war coolant going through it and that seemed to thaw things out.
This morning I fired it up in my driveway and watched, same thing until the engine got warm.

Never had this problem before, but noew that I think of it why doesn't it frost up all the time until the engine gets warm, what's sposed to prevent this and what's causing it now?

I have noticed my coolant needs topping up every week, could my vaporizer be leaking coolant into the propane so I'm acyually burning some coolant in my fuel?

thanks
Will

[Frank]

The reason your vaporizer is frosting up is because there is insufficient coolant flow through the heat exchanger in the vaporizer. I don't know why you would have this problem only when it's warm but I think when you find the location of the leak, you might find the answer.

If your vaporizer is an Impco Model E or a vaporizer very similar to it, I think that it is very unlikely that coolant is mixing with the fuel. On an Impco, the propane in the heat exchanger will be at about the same pressure as the tank so fuel would leak into the coolant rather than the other way around.

Do a pressure test on the engine (without the engine running) and try to determine the location of the leak. I would also check the nozzles on the engine, the hoses, and any wyes or tees for blockage. Rather than disassembling the heat exchanger right away, see if the water side of the heat exchanger is blocked with a garden hose while you have the hoses off. Since you have been driving your truck for years, flush out the entire cooling system and refill with fresh coolant once you have fixed the leak.

Let us know how you make out.

Frank

[Guest]

Yah, that's what it was, I recently changed the rad and had a bit of a leak at the lower rad hose, tightened it up, added some A/F and good to go.

BTW, I had my conversion done back in 92 or so, propane conversions aren't as popular as they used to be are they?
I have no regrets, I think my valves are shot though, if I idle at a light for a long time I get a big puff of blue when I start off.

Thanks
Will

[Guest]

Yah, that's what it was, I recently changed the rad and had a bit of a leak at the lower rad hose, tightened it up, added some A/F and good to go.

BTW, I had my conversion done back in 92 or so, propane conversions aren't as popular as they used to be are they?
I have no regrets, I think my valves are shot though, if I idle at a light for a long time I get a big puff of blue when I start off.

Thanks
Will

[Fisherguy]

Oops, ...

[Frank]

I'm glad it was such an easy fix. I'm not sure why you were getting frosting when your engine warmed up, though. It might have something to do with the water being diverted to the rad when the thermostat opened up.

About that blue smoke. I think it's more sign of your valve seals getting hard than wear on the valve seat. You can get an idea of the condition of your valves with a compression test and with pressurizing the cylinders with some compressed air. If the smoke becomes more of a problem, you could try changing the seals without removing the heads. If your compression is low, freshening-up the heads is the way to go.

You're right about the declining popularity of propane conversions. I think that governments helped the popularity back then by offering tax incentives. Natural gas conversions seem to be getting more attention nowadays.

Frank