Wingnutt
Petty Officer 1st Class
- Joined
- Jul 16, 2003
- Messages
- 255
Re: omc thermostat housing
I had the same problem with my original OMC housing. The thing was so corroded that the O-ring wouldn't hold the thermostat in place any longer. I ended up trying several aftermarket options and like you are experiencing, they didn't work out quite right. I did find one NOS housing at Jackson's Marine in North East Md, but wasn't about to drop $177 for a t-stat housing.
After a lot of research, I found that there was an overlap in parts usage between Volvo and OMC in the early 90's after Volvo purchased OMC where some parts were mixed and matched to get rid of the remaining OMC inventory. IIRC, I ended up using a housing from a '92 Volvo 5.7 that works just fine. the only problem is that the mixing area for the raw water and the hot water coming out of the engine is a bit larger than the original OMC housing, and the temp sensor sets higher than the original location. This results in an accurate temp reading at idle with the 160 degree t-stat, but the temp reading will quickly drop below 120 once the RPMs come up. I've checked and re-checked the operating temperatures with an inferred thermometer and every place on the engine is operating at the correct temp.
Another option is to plug the temp sender hole in the t-stat housing and use the fitting on the left side (looking from the front of the engine) of the intake manifold. If you go this route, be advised that this fitting taps directly in the water jacket surrounding the exhaust port of the cylinder. This location will give an accurate temp at running RPMs, but will climb to over 220 degrees when coming off plane due to the thermostat closing and restricting the water flow through the water jacket. This was a bit unnerving to me, so I moved the temp sender back to the t-stat housing and re-verified that the engine was operating at the correct temperature with my inferred thermometer.
I had the same problem with my original OMC housing. The thing was so corroded that the O-ring wouldn't hold the thermostat in place any longer. I ended up trying several aftermarket options and like you are experiencing, they didn't work out quite right. I did find one NOS housing at Jackson's Marine in North East Md, but wasn't about to drop $177 for a t-stat housing.
After a lot of research, I found that there was an overlap in parts usage between Volvo and OMC in the early 90's after Volvo purchased OMC where some parts were mixed and matched to get rid of the remaining OMC inventory. IIRC, I ended up using a housing from a '92 Volvo 5.7 that works just fine. the only problem is that the mixing area for the raw water and the hot water coming out of the engine is a bit larger than the original OMC housing, and the temp sensor sets higher than the original location. This results in an accurate temp reading at idle with the 160 degree t-stat, but the temp reading will quickly drop below 120 once the RPMs come up. I've checked and re-checked the operating temperatures with an inferred thermometer and every place on the engine is operating at the correct temp.
Another option is to plug the temp sender hole in the t-stat housing and use the fitting on the left side (looking from the front of the engine) of the intake manifold. If you go this route, be advised that this fitting taps directly in the water jacket surrounding the exhaust port of the cylinder. This location will give an accurate temp at running RPMs, but will climb to over 220 degrees when coming off plane due to the thermostat closing and restricting the water flow through the water jacket. This was a bit unnerving to me, so I moved the temp sender back to the t-stat housing and re-verified that the engine was operating at the correct temperature with my inferred thermometer.
