Low operating temp

[jms02050]

My MD7A won't go past 100 degrees. This is based on both the temp gauge and readings from an infrared temp gun with readings taken on the engine and at the exhaust outlet.

This all started about a day after replacing an impeller due to reduced exhaust flow and high operating temps. Now it runs cold. I replaced the t-stat and tested the gauge which is accurate based on the gun readings. Still runs too cool, even under heavy load for a couple of hours.

I'm stumped. Any ideas would be greatly appreciated.

Thanks.

[Parfait's Provider]

Sounds like a bad temp gauge and a not-so-accurate infrared gauge running in Centigrade instead of Farenheit. Can you touch the water inlet to the mixing elbow without hurting yourself?

If it is really running that cold under heavy load, be certain to figure out why because it ought to be patented and you could be a rich person.

[Kurt]

Also sounds like a bad or improperly installed themostat.

[sgbernd]

Any chance the thermostat is in backwards, so the bypass is closed (too cold) and the the engine is functioning as the bybass?

[jms02050]

The exhaust flow is warm to the touch and the gun, which I borrowed from a local small engine repair shop, is accurate and in Fahrenheit. FWIW, 100 degrees C would be about 210 F, so the flow would be very hot to the touch.

A little more background...

When I removed the impeller earlier in the season, I was missing a full vane and a portion of another. I figured the pieces went straight through then engine. The engine, temp gauge, and flow all looked good for 1 day, then I thought the gauge quit on me.

- I tested the gauge by grounding it out (it passed)
- Checked voltage from sender to gauge (it passed)
- Installed a new Volvo thermostat (which only fits in 1 way). Still too cold
- Pulled and tested thermostat (it pass)
- Tested with the temp gun- read 100 F.

I just spoke to a local mechanic today who said that the coolant water is most likely being restricted to the bypass(?) and preventing the engine from coming up to temperature.

This has me thinking that the vane may somehow have blocked something 1 day after the impeller change. Note that I didn't notice any pieces/blockages during the impeller or t-stat change.

Now I'm looking to rule out a blockage or fix it. I'm wondering if backflushing may help? If so, any advice on performing a backflush on an MD7A? I understand the theory but not the application.

[Parfait's Provider]

OK, so the gauges are both in Farenheit, but you can touch the water injection which means it is a lot less than hot water out of a residential water heater at 140 °F or so; I'm guessing the Volvo thermostat is, what, 160°F or 180°F ?

The raw water must be getting past the thermostat somehow. If the cooling passages were blocked would the raw water run by the temp sensor and then out? Doesn't seem normal to me, but then, I have this engineering mind that tries to make sense out of stuff.

Does the engine run any differently temperature-wise without the "good" thermostat? Any chance it works in your saucepan, but not in the housing?